Lignin, a macromolecule found in all vascular plants, can be used as a biomarker for terrestrial dissolved organic matter in the ocean. Measuring lignin in the ocean can help us quantify the supply to and fate of terrestrial carbon in the ocean. Lignin analyses in aquatic samples quantify phenolic products after cupric oxidation using gas or liquid chromatography, with detection either by mass spectrometry or UV-Vis spectroscopy. Mass spectrometry yields low detection limits and high specificity, but requires specialized and expensive instrumentation. In contrast, liquid chromatography coupled with UV-Vis spectroscopy is more readily available and cheaper to operate, but traditionally suffers from lower specificity due to overlapping signals of the bulk organic matter background.
This study demonstrates a new approach of UV-Vis spectroscopic detection coupled to high-performance liquid chromatography (HPLC) that circumvents common issues and improves the detection limit by a factor of 10. This improvement is accomplished by using the second derivative of the chromatogram and applying a modified parallel factor analysis (PARAFAC2). PARAFAC2 tolerates subtle remaining chromatogram shifts in retention time between samples and successfully separates spectra of co-eluting signals. The isolation of spectra based on this machine learning approach improves both lignin phenol identification and the accuracy of their quantification. The approach developed automates the analysis of chromatograms and considerably reduces the water volumes required, improving the applicability of HPLC-UV-Vis for lignin characterization, which may increase the feasibility for widespread use.
}, publisher={Copernicus GmbH}, author={Jensen, Anders Dalhoff Bruhn and Wünsch, Urban and Osburn, Christopher Lee and Stedmon, Colin Andrew}, year={2022}, month={Mar} } @article{lebrasse_schaeffer_zimmerman_hill_coffer_whitman_salls_graybill_osburn_2022, title={Simulated response of St. Joseph Bay, Florida, seagrass meadows and their belowground carbon to anthropogenic and climate impacts}, volume={179}, ISSN={["1879-0291"]}, DOI={10.1016/j.marenvres.2022.105694}, abstractNote={Seagrass meadows are degraded globally and continue to decline in areal extent due to human pressures and climate change. This study used the bio-optical model GrassLight to explore the impact of climate change and anthropogenic stressors on seagrass extent, leaf area index (LAI) and belowground organic carbon (BGC) in St. Joseph Bay, Florida, using water quality data and remotely-sensed sea surface temperature (SST) from 2002 to 2020. Model predictions were compared with satellite-derived measurements of seagrass extent and shoot density from the Landsat images for the same period. The GrassLight-derived area of potential seagrass habitat ranged from 36.2 km}, journal={MARINE ENVIRONMENTAL RESEARCH}, author={Lebrasse, Marie Cindy and Schaeffer, Blake A. and Zimmerman, Richard C. and Hill, Victoria J. and Coffer, Megan M. and Whitman, Peter J. and Salls, Wilson B. and Graybill, David D. and Osburn, Christopher L.}, year={2022}, month={Jul} } @article{lebrasse_schaeffer_coffer_whitman_zimmerman_hill_islam_li_osburn_2022, title={Temporal Stability of Seagrass Extent, Leaf Area, and Carbon Storage in St. Joseph Bay, Florida: a Semi-automated Remote Sensing Analysis}, volume={3}, ISSN={["1559-2731"]}, DOI={10.1007/s12237-022-01050-4}, abstractNote={AbstractSeagrasses are globally recognized for their contribution to blue carbon sequestration. However, accurate quantification of their carbon storage capacity remains uncertain due, in part, to an incomplete inventory of global seagrass extent and assessment of its temporal variability. Furthermore, seagrasses are undergoing significant decline globally, which highlights the urgent need to develop change detection techniques applicable to both the scale of loss and the spatial complexity of coastal environments. This study applied a deep learning algorithm to a 30-year time series of Landsat 5 through 8 imagery to quantify seagrass extent, leaf area index (LAI), and belowground organic carbon (BGC) in St. Joseph Bay, Florida, between 1990 and 2020. Consistent with previous field-based observations regarding stability of seagrass extent throughout St. Joseph Bay, there was no temporal trend in seagrass extent (23 ± 3 km2, τ = 0.09, p = 0.59, n = 31), LAI (1.6 ± 0.2, τ = -0.13, p = 0.42, n = 31), or BGC (165 ± 19 g C m−2, τ = - 0.01, p = 0.1, n = 31) over the 30-year study period. There were, however, six brief declines in seagrass extent between the years 2004 and 2019 following tropical cyclones, from which seagrasses recovered rapidly. Fine-scale interannual variability in seagrass extent, LAI, and BGC was unrelated to sea surface temperature or to climate variability associated with the El Niño-Southern Oscillation or the North Atlantic Oscillation. Although our temporal assessment showed that seagrass and its belowground carbon were stable in St. Joseph Bay from 1990 to 2020, forecasts suggest that environmental and climate pressures are ongoing, which highlights the importance of the method and time series presented here as a valuable tool to quantify decadal-scale variability in seagrass dynamics. Perhaps more importantly, our results can serve as a baseline against which we can monitor future change in seagrass communities and their blue carbon.}, journal={ESTUARIES AND COASTS}, author={Lebrasse, Marie Cindy and Schaeffer, Blake A. and Coffer, Megan M. and Whitman, Peter J. and Zimmerman, Richard C. and Hill, Victoria J. and Islam, Kazi A. and Li, Jiang and Osburn, Christopher L.}, year={2022}, month={Mar} } @article{gonçalves-araujo_granskog_osburn_stedmon_2021, title={A pan-Arctic algorithm for DOC concentrations from CDOM spectra}, url={https://doi.org/10.5194/egusphere-egu21-12720}, DOI={10.5194/egusphere-egu21-12720}, abstractNote={Seagrasses are often considered important players in the global carbon cycle, due to their role in sequestering and protecting sedimentary organic matter as “Blue Carbon”. However, in shallow calcifying systems the ultimate role of seagrass meadows as a sink or source of atmospheric CO2 is complicated by carbonate precipitation and dissolution processes, which produce and consume CO2, respectively. In general, microbial sulfate, iron, and nitrate reduction produce total alkalinity (TA), and the reverse reaction, the re-oxidation of the reduced species, consumes TA. Therefore, net production of TA only occurs when these reduced species are protected from re-oxidation, for example through the burial of FeSx or the escape of N2. Seagrasses also affect benthic biogeochemistry by pumping O2 into the rhizosphere, which for example may allow for direct H2S oxidation.
Our study investigated the role of these factors and processes (seagrass density, sediment biogeochemistry, carbonate precipitation/dissolution, and ultimately air-sea CO2 exchange), on CO2 source-sink behavior in a shallow calcifying (carbonate content ~90%) seagrass meadow (Florida Bay, USA), dominated by Thalassia testudinum. We collected sediment cores from high and low seagrass density areas for flow through core incubations (N2, O2, DI13C, sulfide, DO13C flux), solid phase chemistry (metals, PO13C, Ca13C18O3, AVS: FeS + H2S, CRS: FeS2 + S0), and porewater chemistry (major cations, DI13C, sulfide, 34S18O4). An exciting aspect of this study is that it was conducted inside the footprint of an Eddy Covariance tower (air-sea CO2 exchange), allowing us to directly link benthic processes with CO2 sink-source dynamics.
During the course of our week long study, the seagrass meadow was a consistent source of CO2 to the atmosphere (610 ± 990 µmol·m-2·hr-1). Elevated porewater DIC near 15 cmbsf suggests rhizosphere O2 induced carbonate dissolution, while consumption of DIC in the top 5-10 cm suggests reprecipitation. With high seagrass density, enriched δ13CDIC in the DIC maximum zone (10-25 cm) suggests continual reworking of the carbonates through dissolution/precipitation processes towards more stable PIC, indicating that seagrasses can promote long-term stability of PIC. We constructed a simple elemental budget, which suggests that net alkalinity consumption by ecosystem calcification explains >95% of the observed CO2 emissions. Net alkalinity production through net denitrification (and loss of N2) and net sulfate reduction (and subsequent burial of FeS2 + S0), as well as observed organic carbon burial, could only minimally offset ecosystem calcification.
}, author={Zeller, Mary and Dam, Bryce Van and Lopes, Christian and Smyth, Ashley and Böttcher, Michael and Osburn, Christopher and Zimmerman, Tristan and Pröfrock, Daniel and Fourqurean, James and Thomas, Helmuth}, year={2021}, month={Mar} } @article{gonçalves‐araujo_stedmon_steur_osburn_granskog_2020, title={A Decade of Annual Arctic DOC Export With Polar Surface Water in the East Greenland Current}, url={https://doi.org/10.1029/2020GL089686}, DOI={10.1029/2020GL089686}, abstractNote={AbstractThe export of dissolved organic carbon (DOC) from the Arctic Ocean is expected to change due to warming and increased river runoff. Here we present a method to quantify DOC transport with the East Greenland Current combining synoptic and year‐round data (2009–2018). An algorithm based on quantitative and qualitative aspects of colored dissolved organic matter (CDOM) was developed to provide DOC estimates. Combined with mooring‐derived monthly Polar Surface Water (PSW) volume transports, we estimate DOC exports for the period from 2003–2017. For much of the period DOC exports have been reasonably constant at 46.8 (±6.2) Tg yr−1, while the reduction in PSW export in recent years has resulted in lower annual DOC exports (below 39 Tg C yr−1). We now have a technique to resolve seasonal and annual fluctuations in Arctic carbon export, offering a significant improvement over earlier bulk estimates and represents a baseline to detect future change.}, journal={Geophysical Research Letters}, author={Gonçalves‐Araujo, Rafael and Stedmon, Colin A. and Steur, Laura and Osburn, Christopher L. and Granskog, Mats A.}, year={2020}, month={Oct} } @article{whitby_planquette_cassar_bucciarelli_osburn_janssen_cullen_gonzalez_voelker_sarthou_2020, title={A call for refining the role of humic-like substances in the oceanic iron cycle}, volume={10}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-020-62266-7}, abstractNote={AbstractPrimary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the iron-binding ligand pool throughout the water column. We demonstrate how maximum dissolved iron concentrations could be limited by the concentration and binding capacity of humic ligands, and provide a summary of the key processes that could influence these parameters. If this relationship is globally representative, humics could impose a concentration threshold that buffers the deep ocean iron inventory. This study highlights the dearth of humic data, and the immediate need to measure electroactive humics, dissolved iron and iron-binding ligands simultaneously from surface to depth, across different ocean basins.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Whitby, Hannah and Planquette, Helene and Cassar, Nicolas and Bucciarelli, Eva and Osburn, Christopher L. and Janssen, David J. and Cullen, Jay T. and Gonzalez, Aridane G. and Voelker, Christoph and Sarthou, Geraldine}, year={2020}, month={Apr} } @article{fork_osburn_heffernan_2020, title={Bioavailability and compositional changes of dissolved organic matter in urban headwaters}, volume={82}, url={https://doi.org/10.1007/s00027-020-00739-7}, DOI={10.1007/s00027-020-00739-7}, number={4}, journal={Aquatic Sciences}, publisher={Springer Science and Business Media LLC}, author={Fork, Megan L. and Osburn, Christopher L. and Heffernan, James B.}, year={2020}, month={Oct} } @article{dane_anderson_osburn_colbourne_frisch_2020, title={Centennial clonal stability of asexual Daphnia in Greenland lakes despite climate variability}, url={https://doi.org/10.1002/ece3.7012}, DOI={10.1002/ece3.7012}, abstractNote={AbstractClimate and environmental condition drive biodiversity at many levels of biological organization, from populations to ecosystems. Combined with paleoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long‐term fate of asexual lineages. Here, we provide information on obligately asexual, triploid Daphnia populations from three Arctic lakes in West Greenland through the past 200–300 years to test the impact of environmental change on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake‐specific clonal composition over time. Palaeolimnological reconstructions show considerable regional environmental fluctuations since 1,700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250–300 years. We discuss possible explanations for the apparent population genetic stability: (a) persistent clones are general‐purpose genotypes that thrive under broad environmental conditions, (b) clonal lineages evolved subtle genotypic differences unresolved by microsatellite markers, or (c) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions.}, journal={Ecology and Evolution}, author={Dane, Maison and Anderson, Nicholas John and Osburn, Christopher L. and Colbourne, John K. and Frisch, Dagmar}, year={2020}, month={Dec} } @article{dane_anderson_osburn_colbourne_frisch_2020, title={Centennial clonal stability of asexualDaphniain Greenland lakes despite climate variability}, url={https://doi.org/10.1101/2020.07.22.208553}, DOI={10.1101/2020.07.22.208553}, abstractNote={AbstractClimate and environmental condition drive biodiversity at many levels of biological organisation, from populations to ecosystems. Combined with palaeoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long-term fate of asexual lineages. Here, we provide information on obligately asexual, triploidDaphniapopulations from three Arctic lakes in West Greenland through the past 200-300 years to test the impact of a changing environment on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake-specific clonal composition over time. Palaeolimnological reconstructions show considerable environmental fluctuations since 1700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250-300 years. We discuss three possible explanations for the apparent population genetic stability: (1) the persistent clones are general purpose genotypes that thrive under broad environmental conditions, (2) clonal lineages evolved subtle genotypic differences that are unresolved by microsatellite markers, or (3) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results will motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions.}, author={Dane, Maison and Anderson, N. John and Osburn, Christopher L. and Colbourne, John K. and Frisch, Dagmar}, year={2020}, month={Jul} } @article{bhattacharya_osburn_2021, title={Chromophoric dissolved organic matter composition and load from a coastal river system under variable flow regimes}, volume={760}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2020.143414}, abstractNote={Chromophoric dissolved organic matter (CDOM) exported from riverine catchments can influence biogeochemical processes in coastal environments with implications for water quality and carbon budget. Despite recent efforts to quantify C fluxes during high flow events, knowledge gaps exist regarding the fluxes and yield of terrestrial, reactive vs. recalcitrant CDOM under episodic to base-flow conditions from uplands to downstream estuaries. We used stream dissolved organic carbon (DOC) concentrations and CDOM optical properties using parallel factor analysis to characterize composition and fluxes under variable flow conditions for a coastal river basin in the SE USA. Our findings showed that episodic flows (>75th percentile) were marked by the elevated flux of humic acid-like CDOM and lower in-stream autochthonous production, or microbial degradation. Further, 70% of the terrestrial CDOM was exported during high flows, with a 3-fold increase in CDOM flux during episodic events, including Hurricane Irene in 2011. While, low flows (<25th percentile) were marked by an increased abundance of microbial, humic CDOM that can be easily processed within the estuary. Due to greater wetland coverage in the Neuse, the annual CDOM yield was 5–6 times higher than the larger rivers, such as the Mississippi, USA, and Changjiang, China. We suggest that similar coastal watersheds in SE USA or elsewhere may contribute substantial amounts of reactive CDOM to the estuaries during high flow conditions and can have negative water quality implications for the coastal C dynamics. These findings can help predict the evolution of coastal C cycling under projected climate change and inform the development of appropriate management strategies.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Bhattacharya, Ruchi and Osburn, Christopher L.}, year={2021}, month={Mar} } @article{fowler_osburn_saros_2020, title={Climate‐Driven Changes in Dissolved Organic Carbon and Water Clarity in Arctic Lakes of West Greenland}, url={https://doi.org/10.1029/2019JG005170}, DOI={10.1029/2019JG005170}, abstractNote={AbstractTo assess climate‐mediated terrestrial‐aquatic linkages in Arctic lakes and potential impacts on light attenuation and carbon cycling, we evaluated lake responses to climate drivers in two areas of west Greenland with differing climate patterns. We selected four lakes in a warmer, drier area to compare with four lakes from a cooler, wetter area proximal to the Greenland Ice Sheet. In June from 2013–2018, we measured epilimnetic water temperature, 1% depth of photosynthetically active radiation (PAR), dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA254), DOC‐normalized absorbance at 380 nm (a*380), and chlorophyll a. Interannual coherence of 1% PAR and DOC was particularly high for lakes within the warmer, drier area. This coherence suggests forcing of Arctic lake features by a large‐scale driver, likely climate. Redundancy analysis showed that monthly average precipitation, winter North Atlantic Oscillation (NAO) index (NAOW), spring average air temperature, and spring average precipitation influenced the lake variables (p = 0.003, adj. R2 = 0.58). In particular, monthly average precipitation contributed to increases in soil‐derived DOC quality metrics and chlorophyll a and decreased 1% PAR. Interannual changes in lake responses to climate drivers were more apparent in the warmer, drier area than the cooler, wetter area. The interannual lake responses within and between areas, associated with climate trends, suggest that with ongoing rapid climate change in the Arctic, there could be widespread impacts on key lake responses important for light attenuation and carbon cycling.}, journal={Journal of Geophysical Research: Biogeosciences}, author={Fowler, Rachel A. and Osburn, Christopher L. and Saros, Jasmine E.}, year={2020}, month={Feb} } @article{paerl_claudio_shields_bianchi_osburn_2020, title={Dityrosine formation via reactive oxygen consumption yields increasingly recalcitrant humic‐like fluorescent organic matter in the ocean}, url={https://doi.org/10.1002/lol2.10154}, DOI={10.1002/lol2.10154}, abstractNote={AbstractMarine dissolved organic matter (DOM) is a massive elemental pool on Earth and is thought to consist of a chemically complex mixture of molecules. Part of marine DOM is fluorescent (FDOM) and includes humic‐like compounds. The chemical composition of, and biochemical pathways that yield, autochthonous humic‐like FDOM in the ocean is largely unknown. Inspired by medical and biochemical research detailing the formation of colored and fluorescent dityrosine via peroxidase mediated reactions, we used fluorometry and spectroscopy and found dityrosine exhibits humic‐like fluorescence similar to that of marine FDOM. Investigating its recalcitrance, we conducted short‐term nutrient‐addition and light exposure experiments with dityrosine and found it is resistant to respiration or assimilation by marine microbial communities, yet readily photodegraded. The formation and characteristics of dityrosine newly points to polymerization via reactive oxygen quenching, under aphotic and putatively photic conditions, as an explanation for autochthonous, humic‐like, (semi‐)recalcitrant DOM in the ocean.}, journal={Limnology and Oceanography Letters}, author={Paerl, Ryan W. and Claudio, Iliana M. and Shields, Michael R. and Bianchi, Thomas S. and Osburn, Christopher L.}, year={2020}, month={Oct} } @article{asmala_osburn_paerl_paerl_2021, title={Elevated organic carbon pulses persist in estuarine environment after major storm events}, volume={6}, ISSN={["2378-2242"]}, url={https://doi.org/10.1002/lol2.10169}, DOI={10.1002/lol2.10169}, abstractNote={AbstractEstuaries regulate transport of dissolved organic carbon (DOC) from land to ocean. Export of terrestrial DOC from coastal watersheds is exacerbated by increasing major rainfall and storm events and human activities, leading to pulses of DOC that are shunted through rivers downstream to estuaries. Despite an upward trend of extreme events, the fate of the pulsed terrestrial DOC in estuaries remains unclear. We analyzed the effects of seven major tropical cyclones (TC) from 1999 to 2017 on the quantity and fate of DOC in the Neuse River Estuary (NC, USA). Significant TC‐induced increases in DOC were observed throughout the estuary; the increase lasting from around 50 d at head‐of‐tide to over 6 months in lower estuary. Our results suggest that pulsed terrestrial DOC associated with TCs temporarily overwhelms the estuarine filter's abiotic and biotic degradation capacity under such high flow events, enhancing the shunt of terrestrial carbon to the coastal ocean.}, number={1}, journal={LIMNOLOGY AND OCEANOGRAPHY LETTERS}, publisher={Wiley}, author={Asmala, Eero and Osburn, Christopher L. and Paerl, Ryan W. and Paerl, Hans W.}, year={2021}, month={Feb}, pages={43–50} } @article{asmala_osburn_paerl_paerl_2020, title={Pulsed terrestrial organic carbon persists in an estuarine environment after major storm events}, volume={3}, url={https://doi.org/10.5194/egusphere-egu2020-8587}, DOI={10.5194/egusphere-egu2020-8587}, abstractNote={The transport of dissolved organic carbon from land to ocean is a large and dynamic component of the global carbon cycle. Export of dissolved organic carbon from watersheds is largely controlled by hydrology, and is exacerbated by increasing major rainfall and storm events, causing pulses of terrestrial dissolved organic carbon (DOC) to be shunted through rivers downstream to estuaries. Despite this increasing trend, the fate of the pulsed terrestrial DOC in estuaries remains uncertain. Here we present DOC data from 1999 to 2017 in Neuse River Estuary (NC, USA) and analyze the effect of six tropical cyclones (TC) during that period on the quantity and fate of DOC in the estuary. We find that that TCs promote a considerable increase in DOC concentration near the river mouth at the entrance to the estuary, on average an increase of 200 µmol l-1 due to storms was observed. TC-induced increases in DOC are apparent throughout the estuary, and the duration of these elevated DOC concentrations ranges from one month at the river mouth to over six months in lower estuary. Our results suggest that despite the fast mineralization rates, the terrestrial DOC is processed only to a minor extent relative to the pulsed amount entering the estuary. We conclude that the vast quantity of organic carbon delivered to estuaries by TCs transform estuaries from active biogeochemical processing “reactors” of organic carbon to appear more like passive shunts due to the sheer amount of pulsed material rapidly flushed through the estuary.
}, publisher={Copernicus GmbH}, author={Asmala, Eero and Osburn, Christopher and Paerl, Ryan and Paerl, Hans}, year={2020}, month={Mar} } @article{paerl_hall_hounshell_rossignol_barnard_luettich_rudolph_osburn_bales_harding_2020, title={Recent increases of rainfall and flooding from tropical cyclones (TCs) in North Carolina (USA): implications for organic matter and nutrient cycling in coastal watersheds}, volume={150}, ISSN={["1573-515X"]}, DOI={10.1007/s10533-020-00693-4}, abstractNote={Coastal North Carolina experienced 36 tropical cyclones (TCs), including three floods of historical significance in the past two decades (Hurricanes Floyd-1999, Matthew-2016 and Florence-2018). These events caused catastrophic flooding and major alterations of water quality, fisheries habitat and ecological conditions of the Albemarle-Pamlico Sound (APS), the second largest estuarine complex in the United States. Continuous rainfall records for coastal NC since 1898 reveal a period of unprecedented high precipitation storm events since the late-1990s. Six of seven of the "wettest" storm events in this > 120-year record occurred in the past two decades, identifying a period of elevated precipitation and flooding associated with recent TCs. We examined storm-related freshwater discharge, carbon (C) and nutrient, i.e., nitrogen (N) and phosphorus (P) loadings, and evaluated contributions to total annual inputs in the Neuse River Estuary (NRE), a major sub-estuary of the APS. These contributions were highly significant, accounting for > 50% of annual loads depending on antecedent conditions and storm-related flooding. Depending on the magnitude of freshwater discharge, the NRE either acted as a "processor" to partially assimilate and metabolize the loads or acted as a "pipeline" to transport the loads to the APS and coastal Atlantic Ocean. Under base-flow, terrestrial sources dominate riverine carbon. During storm events these carbon sources are enhanced through the inundation and release of carbon from wetlands. These findings show that event-scale discharge plays an important and, at times, predominant role in C, N and P loadings. We appear to have entered a new climatic regime characterized by more frequent extreme precipitation events, with major ramifications for hydrology, cycling of C, N and P, water quality and habitat conditions in estuarine and coastal waters.}, number={2}, journal={BIOGEOCHEMISTRY}, author={Paerl, Hans W. and Hall, Nathan S. and Hounshell, Alexandria G. and Rossignol, Karen L. and Barnard, Malcolm A. and Luettich, Richard A., Jr. and Rudolph, Jacob C. and Osburn, Christopher L. and Bales, Jerad and Harding, Lawrence W., Jr.}, year={2020}, month={Sep}, pages={197–216} } @misc{ward_megonigal_bond-lamberty_bailey_butman_canuel_diefenderfer_ganju_goni_graham_et al._2020, title={Representing the function and sensitivity of coastal interfaces in Earth system models}, volume={11}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-020-16236-2}, abstractNote={AbstractBetween the land and ocean, diverse coastal ecosystems transform, store, and transport material. Across these interfaces, the dynamic exchange of energy and matter is driven by hydrological and hydrodynamic processes such as river and groundwater discharge, tides, waves, and storms. These dynamics regulate ecosystem functions and Earth’s climate, yet global models lack representation of coastal processes and related feedbacks, impeding their predictions of coastal and global responses to change. Here, we assess existing coastal monitoring networks and regional models, existing challenges in these efforts, and recommend a path towards development of global models that more robustly reflect the coastal interface.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Ward, Nicholas D. and Megonigal, J. Patrick and Bond-Lamberty, Ben and Bailey, Vanessa L. and Butman, David and Canuel, Elizabeth A. and Diefenderfer, Heida and Ganju, Neil K. and Goni, Miguel A. and Graham, Emily B. and et al.}, year={2020}, month={May} } @article{rudolph_arendt_hounshell_paerl_osburn_2020, title={Use of Geospatial, Hydrologic, and Geochemical Modeling to Determine the Influence of Wetland-Derived Organic Matter in Coastal Waters in Response to Extreme Weather Events}, volume={7}, ISSN={["2296-7745"]}, DOI={10.3389/fmars.2020.00018}, abstractNote={Flooding from extreme weather events (EWE), such as hurricanes, exports large amounts of dissolved organic matter (DOM) to both estuaries and coastal waters globally. Hydrologic connectivity of wetlands to adjacent river channels during flood events can potentially have a major control on the DOM exported to coastal waters after EWEs. In this study, a geographic information system based flood model was used to: (1) determine the volume of flooded wetlands in a river corridor following Hurricane Matthew in 2016; (2) compute the resulting volume fluxes of DOM to the Neuse River Estuary-Pamlico Sound (NRE-PS), in eastern North Carolina and (3) use the flood model to quantify the wetland contribution to DOM export. The flood model-derived contributions were validated with a Bayesian Monte Carlo mixing model combining measurements of DOM quality: specific UV Absorbance at 254 nm (SUVA254), spectral slope ratio (SR), and stable isotope ratios of dissolved organic carbon (δ13C-DOC). Results indicated that (1) hydrologic connectivity of the freshwater riparian wetlands caused the wetlands to become the primary source of organic matter (OM) that was exported into the NRE-PS after Matthew and (2) this source lingered in these coastal waters in the months after the storm. Thus, in consideration of the pulse-shunt concept, EWE such as Hurricane Matthew cause pulses of DOM from wetlands, which were the primary source of the OM shunted from the terrestrial environment to the estuary and sound. Wetlands constituted ca. 48% of the annual loading of DOC into the NRE and 16% of DOC loading into the PS over a period of 30 days after Hurricane Matthew. Results were consistent with prior studies in this system, and other coastal ecosystems, that attributed a high reactivity of DOM as the underlying reason for large CO2 releases following EWE. Adapting the pulse-shunt concept to estuaries requires the addition of a “processing” step to account for the DOM to CO2 dynamics, thus a new pulse-shunt process is proposed to incorporate coastal waters. Our results suggest that with increasing frequency and intensity of EWE, strengthening of the lateral transfer of DOM from land to ocean will occur and has the potential to greatly impact coastal carbon cycling.}, journal={FRONTIERS IN MARINE SCIENCE}, author={Rudolph, Jacob C. and Arendt, Carli A. and Hounshell, Alexandria G. and Paerl, Hans W. and Osburn, Christopher L.}, year={2020}, month={Feb} } @article{osburn_atar_boyd_montgomery_2019, title={Antecedent precipitation influences the bacterial processing of terrestrial dissolved organic matter in a North Carolina estuary}, volume={221}, ISSN={["1096-0015"]}, url={https://doi.org/10.1016/j.ecss.2019.03.016}, DOI={10.1016/j.ecss.2019.03.016}, abstractNote={Estuaries and coastal waters ultimately receive the terrestrial dissolved organic matter (DOM) exported from coastal watersheds, more directly during extreme precipitation events. Recent work suggests DOM's degradation in coastal waters varies with its quality, which also might vary as a function of precipitation, activating contributions from different sources within a watershed. The aim of this study was to determine the extent to which microbial degradation of terrestrial DOM in the Newport River Estuary, eastern North Carolina, was influenced by precipitation events occurring within the preceding seven days from sampling. We hypothesized that DOM stored in forested wetlands (e.g., pocosins and Cypress swamps) that become connected to the main channel of the Newport River during high precipitation events was more labile than DOM flowing into the estuary under low precipitation events. DOM quality was assessed with optical and stable C isotope (δ13C) measurements, while DOM lability was assessed by measurements of bacterial production (BP) and mineralization of 14C-labeled phenanthrene (Pmin), a polyaromatic tracer compound. Aromatic content of DOM, assessed by specific ultraviolet absorbance at 254 nm (SUVA254) was highest in the river with values well over 5.0 L mg C−1 m−1, and decreased with salinity. Antecedent precipitation (AP) of at least 100 mm in the seven days prior to sampling resulted in dissolved organic carbon (DOC) concentrations >20 mg L−1, at salinities <10. Similarly, fluorescence humification index (HIX) values were highest in the estuary after the highest AP. Generally depleted δ13C-DOC values (−26 to −28‰) in the estuary up to a salinity of 30 indicated a substantial source of DOM likely originating from the forested swamps and tidal wetlands fringing the estuary. BP exhibited wide variability yet declined with salinity, while median values after higher AP (40 μg C L−1 d−1) were double that under lower AP. By contrast, aromatic mineralization (Pmin) rates increased as both DOC and CDOM concentrations, and SUVA254 and HIX values, declined with salinity. However, Pmin rates were highest after the highest AP for the three events sampled. Results indicate that flooding of coastal wetlands mobilizes a large pool of labile DOM which have a large impact on the carbon cycle in estuaries. By altering the quality, as well as quantity of terrestrial organic matter inputs to estuarine systems, extreme events may also affect utilization of aromatic organics by estuarine microbial assemblages, an intriguing research question worthy of further study.}, journal={ESTUARINE COASTAL AND SHELF SCIENCE}, publisher={Elsevier BV}, author={Osburn, C. L. and Atar, J. N. and Boyd, T. J. and Montgomery, M. T.}, year={2019}, month={May}, pages={119–131} } @article{saros_anderson_juggins_mcgowan_yde_telling_bullard_yallop_heathcote_burpee_et al._2019, title={Arctic climate shifts drive rapid ecosystem responses across the West Greenland landscape}, volume={14}, ISSN={["1748-9326"]}, DOI={10.1088/1748-9326/ab2928}, abstractNote={Abstract Prediction of high latitude response to climate change is hampered by poor understanding of the role of nonlinear changes in ecosystem forcing and response. While the effects of nonlinear climate change are often delayed or dampened by internal ecosystem dynamics, recent warming events in the Arctic have driven rapid environmental response, raising questions of how terrestrial and freshwater systems in this region may shift in response to abrupt climate change. We quantified environmental responses to recent abrupt climate change in West Greenland using long-term monitoring and paleoecological reconstructions. Using >40 years of weather data, we found that after 1994, mean June air temperatures shifted 2.2 °C higher and mean winter precipitation doubled from 21 to 40 mm; since 2006, mean July air temperatures shifted 1.1 °C higher. Nonlinear environmental responses occurred with or shortly after these abrupt climate shifts, including increasing ice sheet discharge, increasing dust, advancing plant phenology, and in lakes, earlier ice out and greater diversity of algal functional traits. Our analyses reveal rapid environmental responses to nonlinear climate shifts, underscoring the highly responsive nature of Arctic ecosystems to abrupt transitions.}, number={7}, journal={ENVIRONMENTAL RESEARCH LETTERS}, author={Saros, Jasmine E. and Anderson, Nicholas John and Juggins, Stephen and McGowan, Suzanne and Yde, Jacob C. and Telling, Jon and Bullard, Joanna E. and Yallop, Marian L. and Heathcote, Adam J. and Burpee, Benjamin T. and et al.}, year={2019}, month={Jul} } @article{eurico j. d'sa_joshi_liu_ko_osburn_bianchi_2019, title={Biogeochemical Response of Apalachicola Bay and the Shelf Waters to Hurricane Michael Using Ocean Color Semi-Analytic/Inversion and Hydrodynamic Models}, volume={6}, ISSN={["2296-7745"]}, DOI={10.3389/fmars.2019.00523}, abstractNote={Hurricanes are increasingly being recognized as important episodic drivers in ocean biogeochemical cycling; however, spatiotemporal response of their impacts on coastal and estuarine ecosystems are limited. Hurricane Michael, which made landfall just west of Apalachicola Bay (ApB) on October 10, 2018 as a Category 5 hurricane with sustained winds of 250 km h-1, caused widespread damage to the northwest Florida coast, and adverse effects on oyster reefs and water quality in ApB due to winds and coastal flooding associated with a strong storm surge. The impact of wind forcing and retreating storm surges on coastal and shelf biogeochemical properties remains however, largely unknown. In this study, we use a combination of pre-hurricane field observations, ocean-color satellite imagery and the outputs (salinity, currents, sea surface height and temperature) of a nested high-resolution 3-dimensional hydrodynamic model (NCOM) to examine the biogeochemical response of ApB and the surrounding shelf waters to Hurricane Michael. MODIS-derived optical proxies (e.g., absorption of colored dissolved organic matter or CDOM and particle backscattering coefficients) of dissolved and particulate organic carbon (DOC and POC) were derived for a series of clear-sky imagery (prior to and following the hurricane) using a combination of estuarine-tuned semi-analytic and empirical algorithms. Following the hurricane, spatiotemporal distribution of both DOC and POC in ApB and the nearshore coastal waters showed a strong response to storm surge, increasing river discharge, currents, and wind field. Average flux estimates of organic carbon exported from ApB between October 5-21, 2018 to the coastal ocean were much greater for DOC (0.86106 kg C d-1) than POC (0.21106 kg C d-1) and increased with increasing river discharge and the wind field. A bio-optical inversion algorithm applied to Sentinel-3A OLCI imagery of 13 October, 2018 immediately following the hurricane’s passage, showed a strong, week-long biological response with spatially distinct phytoplankton blooms of Karenia brevis and Emiliania Huxleyi, as detected by satellite imagery of pigments, an approach that could revolutionize our understanding of environmental impacts on phytoplankton. This study revealed spatiotemporal changes in estuarine and coastal ocean biogeochemistry reflective of a systematic regional ecosystem response to Hurricane Michael.}, journal={FRONTIERS IN MARINE SCIENCE}, author={Eurico J. D'Sa and Joshi, Ishan D. and Liu, Bingqing and Ko, Dong S. and Osburn, Christopher L. and Bianchi, Thomas S.}, year={2019}, month={Aug} } @inbook{osburn_margolin_guo_bianchi_hansell_2019, place={College Station, Texas}, title={Dissolved, Colloidal, and Particulate Organic Matter in the Gulf of Mexico}, booktitle={Gulf of Mexico Origin, Waters, and Biota, Volume 5, Chemical Oceanography}, publisher={Texas A&M University Press}, author={Osburn, C.L. and Margolin, A.R. and Guo, L.D. and Bianchi, T.S. and Hansell, D.A.}, editor={Bianchi, T. S.Editor}, year={2019} } @article{montgomery_collins_boyd_osburn_vargas_lu_2019, title={Eco-friendly Organic Nanotubes Encapsulating Alkaline Phosphatase and Ecotoxicology of Nanotubes to Natural Bacterial Assemblages in Coastal Estuarine Waters}, volume={4}, ISSN={["2470-1343"]}, DOI={10.1021/acsomega.8b02650}, abstractNote={Phosphatase-encapsulated nanotubes have potential in environmental remediation of organophosphate contaminants (e.g., pesticides, nerve agents). We investigated alkaline phosphatase (AP) activity when encapsulated in self-assembled lithocholic acid nanotubes (LCA-AP) in water samples along a transect from Cypress bog headwaters through estuarine waters and to Atlantic Ocean seawater. Apparent Vmax (appVmax) for both LCA-AP and unencapsulated AP (Free-AP) was most rapid at mid-estuary and most inhibited at the humic-rich bog. LCA-AP retained a higher-activity percentage, suggesting that encapsulation may afford some protection from denaturing effects of humics. Apparent Km (appKm) of Free-AP (1–2.3 μM) was largely unaffected by preincubation with transect water, whereas appKm of LCA-AP was higher with bog water (5.3 μM) relative to other stations. When comparing Free-AP and LCA-AP, increasing salinity generally decreased the catalytic efficiency of the LCA-AP, but had little effect on that of the Free-AP. ...}, number={1}, journal={ACS OMEGA}, author={Montgomery, Michael T. and Collins, Greg E. and Boyd, Thomas J. and Osburn, Christopher L. and Vargas, Diana Oviedo and Lu, Qin}, year={2019}, month={Jan}, pages={2196–2205} } @article{hounshell_rudolph_van dam_hall_osburn_paerl_2019, title={Extreme weather events modulate processing and export of dissolved organic carbon in the Neuse River Estuary, NC}, volume={219}, ISSN={["1096-0015"]}, url={https://doi.org/10.1016/j.ecss.2019.01.020}, DOI={10.1016/j.ecss.2019.01.020}, abstractNote={As the interface between riverine and coastal systems, estuaries play a key role in receiving, transporting, and processing terrestrial organic carbon prior to export to downstream coastal systems. Estuaries can switch from terrestrial organic carbon reactors under low river flow to pipelines under high flow, but it remains unclear how estuarine terrestrial organic carbon processing responds to the full spectrum of discharge conditions, which are bracketed by these high and low discharge events. The amount of terrestrial dissolved organic carbon and colored dissolved organic matter imported, processed, and exported was assessed for riverine discharge events spanning from the 4th to 99th flow quantiles in the Neuse River Estuary, North Carolina, USA using spatially and temporally (July 2015–December 2016) resolved measurements. The extent of dissolved organic matter processing in the estuary under various flow conditions was estimated using a non-steady state box model to calculate estuary-wide terrestrial dissolved organic carbon and colored dissolved organic matter source & sink terms. Under mid-range riverine discharge conditions (4th to 89th flow quantiles), the Neuse River Estuary was a sink for terrestrial dissolved organic carbon, retaining and/or processing (i.e., flocculation; photochemical and microbial degradation) on average ∼29% of terrestrial dissolved organic carbon. Following floods due to extreme precipitation events (99th flow quantile), however, over 99% of the terrestrial dissolved organic carbon loaded from the riverine end-member was exported directly to the downstream coastal system. Following such extreme weather events, the estuary acts as a pipeline for direct export of terrestrial dissolved organic carbon, drastically altering the amount and quality of dissolved organic carbon loaded to downstream coastal systems. This has important implications under future climate scenarios, where extreme weather events are expected to increase.}, journal={ESTUARINE COASTAL AND SHELF SCIENCE}, publisher={Elsevier BV}, author={Hounshell, Alexandria G. and Rudolph, Jacob C. and Van Dam, Bryce R. and Hall, Nathan S. and Osburn, Christopher L. and Paerl, Hans W.}, year={2019}, month={Apr}, pages={189–200} } @article{hounshell_rudolph_van dam_hall_osburn_paerl_2019, title={Extreme weather events modulate processing and export of dissolved organic carbon in the Neuse River Estuary, NC (vol 219, pg 189, 2019)}, volume={227}, ISBN={1096-0015}, DOI={10.1016/j.ecss.2019.106328}, journal={ESTUARINE COASTAL AND SHELF SCIENCE}, author={Hounshell, Alexandria G. and Rudolph, Jacob C. and Van Dam, Bryce R. and Hall, Nathan S. and Osburn, Christopher L. and Paerl, Hans W.}, year={2019} } @article{osburn_rudolph_paerl_hounshell_van dam_2019, title={Lingering Carbon Cycle Effects of Hurricane Matthew in North Carolina's Coastal Waters}, volume={46}, ISSN={0094-8276 1944-8007}, url={http://dx.doi.org/10.1029/2019GL082014}, DOI={10.1029/2019GL082014}, abstractNote={AbstractIn 2016, Hurricane Matthew accounted for 25% of the annual riverine C loading to the Neuse River Estuary‐Pamlico Sound, in eastern North Carolina. Unlike inland watersheds, dissolved organic carbon (DOC) was the dominant component of C flux from this coastal watershed and stable carbon isotope and chromophoric dissolved organic matter evidence indicated the estuary and sound were dominated by wetland‐derived terrigenous organic matter sources for several months following the storm. Persistence of wetland‐derived DOC enabled its degradation to carbon dioxide (CO2), which was supported by sea‐to‐air CO2 fluxes measured in the sound weeks after the storm. Under future increasingly extreme weather events such as Hurricane Matthew, and most recently Hurricane Florence (September 2018), degradation of terrestrial DOC in floodwaters could increase flux of CO2 from estuaries and coastal waters to the atmosphere.}, number={5}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Osburn, Christopher L. and Rudolph, Jacob C. and Paerl, Hans W. and Hounshell, Alexandria G. and Van Dam, Bryce R.}, year={2019}, month={Mar}, pages={2654–2661} } @article{shields_bianchi_osburn_kinsey_ziervogel_schnetzer_corradino_2019, title={Linking chromophoric organic matter transformation with biomarker indices in a marine phytoplankton growth and degradation experiment}, volume={214}, ISSN={["1872-7581"]}, DOI={10.1016/j.marchem.2019.103665}, abstractNote={The production and transformation of marine chromophoric dissolved organic matter (CDOM) provides a window into the marine biological pump as it is present at all depths and can be measured both in the field and via satellite. However, outside of lignin for terrestrial DOM, few studies have linked marine CDOM characteristics with biomarker indices. In this study, we quantified five fluorescent components of marine CDOM and base-extractable particulate organic matter (BEPOM) in a growth and degradation experiment using a natural plankton assemblage, and compared those results to bacterial abundances, hydrolytic enzyme activities, and amino acid concentrations and associated diagenetic indices. Rotating glass bottles containing plankton were sampled initially (day 0), during the mid-exponential (day 13) and stationary (day 20) growth phases, and again following a dark degradation period that lasted 42 days. Protein-like fluorescence (tryptophan-like and tyrosine-like) was correlated with the total amino acid concentrations for both the DOM and BEPOM through all phases of the incubation. However, tryptophan-like fluorescence showed a stronger correlation for aromatic amino acids. The concentration of particulate organic carbon changed significantly during each phase of the experiment and this substrate correlated with hydrolytic enzyme activities and bacterial abundance. This heterotrophy diagenetically altered the POM during the stationary phase and ultimately resulted in the increased production of more humic-like CDOM after degradation in the dark. Results from this study indicate that CDOM formation and cycling may play a prominent role in the ocean's nitrogen cycle.}, journal={MARINE CHEMISTRY}, author={Shields, Michael R. and Bianchi, Thomas S. and Osburn, Christopher L. and Kinsey, Joanna D. and Ziervogel, Kai and Schnetzer, Astrid and Corradino, Gabrielle}, year={2019}, month={Aug} } @article{arellano_bianchi_osburn_d'sa_ward_oviedo‐vargas_joshi_ko_shields_kurian_et al._2019, title={Mechanisms of Organic Matter Export in Estuaries with Contrasting Carbon Sources}, volume={124}, ISSN={2169-8953 2169-8961}, url={http://dx.doi.org/10.1029/2018JG004868}, DOI={10.1029/2018JG004868}, abstractNote={AbstractModifications in land use and climate will result in shifts in the magnitude and composition of organic matter (OM) transported from wetlands to coastal waters, but differentiation between riverine and wetland OM sources in coastal areas remains a challenge. Here, we evaluate particulate and dissolved OM export dynamics in two representative estuary geomorphologies—Apalachicola Bay (AP) and Barataria Bay (BB), characterized primarily by blackwater river inputs and high particle abundance, respectively. The magnitude and composition of OM exported from each estuary was evaluated based on seasonal measurements of surface water dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen, the stable isotopic composition of DOC and POC, dissolved and particulate lignin phenols, and carbon‐normalized dissolved lignin‐phenol yields. Data and discriminant analyses support the initial hypothesis; AP is dominated by a more terrestrial source of OM due to importance of fluvial dissolved OM inputs, while BB is a more particle‐rich and wetland carbon‐dominated system. Total lignin export (sum of mean dissolved and mean particulate) was higher in BB (5.73 ± 2.50 × 105 kg/year) than in AP (4.21 ± 2.35 × 105 kg/year). Particulate lignin export from BB was greater than the export of dissolved lignin at either BB or AP, suggesting coastal marsh erosion may be driving this comparatively large export of particulate lignin. These data have important implications for the stability of stored OM in coastal habitats, particularly since such habitats in this region are highly vulnerable due to relative sea level rise.}, number={10}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Arellano, A. R. and Bianchi, T. S. and Osburn, C. L. and D'Sa, E. J. and Ward, N. D. and Oviedo‐Vargas, D. and Joshi, I. D. and Ko, D. S. and Shields, M. R. and Kurian, G. and et al.}, year={2019}, month={Oct}, pages={3168–3188} } @article{van dam_lopes_osburn_fourqurean_2019, title={Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows}, volume={16}, ISSN={["1726-4189"]}, url={https://doi.org/10.5194/bg-16-4411-2019}, DOI={10.5194/bg-16-4411-2019}, abstractNote={Abstract. The net ecosystem productivity (NEP) of two seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles during a short study in the fall of 2018. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air–water gas exchange and contrasting responses to variations in light intensity. We also acknowledge the impact of advective exchange on metabolic calculations of NEP and net ecosystem calcification (NEC) using the “open-water” approach and attempt to quantify this effect. In this first direct determination of NEPDIC in seagrass, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net above-ground primary productivity. NEC was also negative, indicating that both sites were net dissolving carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. However, given the limited spatial (two sites) and temporal (8 d) extent of this study, our results may not be representative of Florida Bay as a whole and may be season-specific. The results of this study highlight the need for better temporal resolution, accurate carbonate chemistry accounting, and an improved understanding of physical mixing processes in future seagrass metabolism studies. }, number={22}, journal={BIOGEOSCIENCES}, publisher={Copernicus GmbH}, author={Van Dam, Bryce R. and Lopes, Christian and Osburn, Christopher L. and Fourqurean, James W.}, year={2019}, month={Nov}, pages={4411–4428} } @article{dam_lopes_osburn_fourqurean_2019, title={Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows}, volume={5}, url={https://doi.org/10.5194/bg-2019-191}, DOI={10.5194/bg-2019-191}, abstractNote={Abstract. The net ecosystem productivity (NEP) of two contrasting seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air-water gas exchange and contrasting responses to variations in light intensity. In this first direct determination of NEPDIC in seagrasses, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net aboveground primary productivity. Net ecosystem calcification (NEC) was also negative, indicating that both sites were net dissolving of carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. Furthermore, a simple budget analysis indicates that these two seagrass meadows have contrasting impacts on pH buffering of adjacent systems, due to variations in the TA : DIC export ratio. The results of this study highlight the need for better temporal resolution, as well as accurate carbonate chemistry accounting in future seagrass metabolism studies. }, publisher={Copernicus GmbH}, author={Dam, Bryce R. Van and Lopes, Christian and Osburn, Christopher L. and Fourqurean, James W.}, year={2019}, month={May} } @article{velasco_artyushkova_ali_osburn_gonzalez-estrella_lezama-pacheco_cabaniss_cerrato_2019, title={Organic Functional Group Chemistry in Mineralized Deposits Containing U(IV) and U(VI) from the Jackpile Mine in New Mexico}, volume={53}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.9b00407}, abstractNote={We investigated the functional group chemistry of natural organic matter (NOM) associated with both U(IV) and U(VI) in solids from mineralized deposits exposed to oxidizing conditions from the Jackpile Mine, Laguna Pueblo, NM. The uranium (U) content in unreacted samples was 0.44-2.6% by weight determined by X-ray fluorescence. In spite of prolonged exposure to ambient oxidizing conditions, ≈49% of U(IV) and ≈51% of U(VI) were identified on U LIII edge extended X-ray absorption fine structure spectra. Loss on ignition and thermogravimetric analyses identified from 13% to 44% of NOM in the samples. Carbonyl, phenolic, and carboxylic functional groups in the unreacted samples were identified by fitting of high-resolution X-ray photoelectron spectroscopy (XPS) C 1s and O 1s spectra. Peaks corresponding to phenolic and carbonyl functional groups had intensities higher than those corresponding to carboxylic groups in samples from the supernatant from batch extractions conducted at pH 13, 7, and 2. U(IV) and U(VI) species were detected in the supernatant after batch extractions conducted under oxidizing conditions by fitting of high-resolution XPS U 4f spectra. The outcomes from this study highlight the importance of the influence of pH on the organic functional group chemistry and U speciation in mineralized deposits.}, number={10}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Velasco, Carmen A. and Artyushkova, Kateryna and Ali, Abdul-Mehdi S. and Osburn, Christopher L. and Gonzalez-Estrella, Jorge and Lezama-Pacheco, Juan S. and Cabaniss, Stephen E. and Cerrato, Jose M.}, year={2019}, month={May}, pages={5758–5767} } @article{paerl_hall_hounshell_luettich_rossignol_osburn_bales_2019, title={Recent increase in catastrophic tropical cyclone flooding in coastal North Carolina, USA: Long-term observations suggest a regime shift}, volume={9}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-019-46928-9}, abstractNote={AbstractCoastal North Carolina, USA, has experienced three extreme tropical cyclone-driven flood events since 1999, causing catastrophic human impacts from flooding and leading to major alterations of water quality, biogeochemistry, and ecological conditions. The apparent increased frequency and magnitudes of such events led us to question whether this is just coincidence or whether we are witnessing a regime shift in tropical cyclone flooding and associated ecosystem impacts. Examination of continuous rainfall records for coastal NC since 1898 reveals a period of unprecedentedly high precipitation since the late-1990’s, and a trend toward increasingly high precipitation associated with tropical cyclones over the last 120 years. We posit that this trend, which is consistent with observations elsewhere, represents a recent regime shift with major ramifications for hydrology, carbon and nutrient cycling, water and habitat quality and resourcefulness of Mid-Atlantic and possibly other USA coastal regions.}, journal={SCIENTIFIC REPORTS}, author={Paerl, Hans W. and Hall, Nathan S. and Hounshell, Alexandria G. and Luettich, Richard A., Jr. and Rossignol, Karen L. and Osburn, Christopher L. and Bales, Jerad}, year={2019}, month={Jul} } @article{bhattacharya_osburn_2020, title={Spatial patterns in dissolved organic matter composition controlled by watershed characteristics in a coastal river network: The Neuse River Basin, USA}, volume={169}, ISSN={0043-1354}, url={http://dx.doi.org/10.1016/j.watres.2019.115248}, DOI={10.1016/j.watres.2019.115248}, abstractNote={The effect of watershed characteristics (land use land cover and morphology) on spatial variability in dissolved organic matter (DOM) composition, and concentrations of dissolved organic carbon [DOC] and nitrogen [DON] was assessed in a coastal river basin draining into Pamlico Sound in eastern North Carolina, USA. Understanding the factors that influence DOM concentration and composition i.e., structurally complex molecules with high molecular weight versus low molecular weight, simple molecules can provide insights on DOM cycling and water composition implications. Such information is imperative for large coastal river networks undergoing rapid and intense land use and land cover (LULC) changes. DOM composition was estimated using optical indices calculated from DOM absorbance and fluorescence measurements. DOM was derived from terrestrial sources, and ordination analysis indicated that LULC, in particular, % wetland area was the most significant control on DOM composition and concentration. Wetland and agricultural coastal streams were abundant in humic and complex DOM, whereas forested and urban streams were least abundant in humic DOM. We speculate that greater availability of mobilizable DOM in wetland and agricultural watersheds contributed to this observation. In comparison, mixed urbanized and forested streams in North Carolina's Piedmont region were abundant in [DOC], less complex, low molecular weight DOM, as well as greater amounts [DON] due to higher urban runoff and elevated DOM production in these streams. Our results indicated that physiographic transition from Piedmont to coastal plain and varying LULC influenced the spatial variability in DOM composition and concentration. Our findings highlight that increasing anthropogenic alterations might increase the abundance of reactive DOM in coastal rivers and estuaries resulting in severe water quality issues. This information is important for monitoring and developing land use policies.}, journal={Water Research}, publisher={Elsevier BV}, author={Bhattacharya, Ruchi and Osburn, Christopher L.}, year={2020}, month={Feb}, pages={115248} } @article{osburn_anderson_leng_barry_whiteford_2019, title={Stable isotopes reveal independent carbon pools across an Arctic hydro‐climatic gradient: Implications for the fate of carbon in warmer and drier conditions}, volume={4}, ISSN={2378-2242 2378-2242}, url={http://dx.doi.org/10.1002/lol2.10119}, DOI={10.1002/lol2.10119}, abstractNote={AbstractArctic lakes are poised for substantial changes to their carbon (C) cycles in the near future. Autochthonous processes in lakes which consume inorganic C and create biomass that can be sequestered in sediments are accompanied by allochthonous inputs of organic matter from the surrounding watershed. Both C sources can be mineralized and degassed as CO2, but also become recalcitrant and accumulate in pelagic waters. Using stable carbon isotope (δ13C) values and elemental ratios as geochemical proxies, we investigated diverse organic matter sources to lakes located across a hydro‐climatic gradient in Southwest Greenland. Particulate organic matter (POM) and sediments were clearly of autochthonous algal origin, while dissolved organic matter (DOM) was a mix between autochthonous macrophytes and allochthonous watershed sources. Our results imply that a warmer and drier Arctic will lead to decoupled C pools: a water column dominated by increasingly autochthonous, macrophytic DOM, and sediments dominated by autochthonous algal POM.}, number={6}, journal={Limnology and Oceanography Letters}, publisher={Wiley}, author={Osburn, Christopher L. and Anderson, N. John and Leng, Melanie J. and Barry, Christopher D. and Whiteford, Erika J.}, year={2019}, month={Sep}, pages={205–213} } @article{dam_lopes_osburn_fourqurean_2019, title={Supplementary material to "Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows"}, volume={5}, url={https://doi.org/10.5194/bg-2019-191-supplement}, DOI={10.5194/bg-2019-191-supplement}, abstractNote={Table S1.Table of physicochemical conditions (TA, DIC, Salinity), as well as seagrass and 2 sediment chemical characteristics (average ± SD).}, publisher={Copernicus GmbH}, author={Dam, Bryce R. Van and Lopes, Christian and Osburn, Christopher L. and Fourqurean, James W.}, year={2019}, month={May} } @article{anderson_leng_osburn_fritz_law_mcgowan_2018, title={A landscape perspective of Holocene organic carbon cycling in coastal SW Greenland lake-catchments}, volume={202}, ISSN={0277-3791}, url={http://dx.doi.org/10.1016/J.QUASCIREV.2018.09.006}, DOI={10.1016/j.quascirev.2018.09.006}, abstractNote={Arctic organic carbon (OC) stores are substantial and have accumulated over millennia as a function of changes in climate and terrestrial vegetation. Arctic lakes are also important components of the regional C-cycle as they are sites of OC production and CO2 emissions but also store large amounts of OC in their sediments. This sediment OC pool is a mixture derived from terrestrial and aquatic sources, and sediment cores can therefore provide a long-term record of the changing interactions between lakes and their catchments in terms of nutrient and C transfer. Sediment carbon isotope composition (δ13C), C/N ratio and organic C accumulation rates (C AR) of 14C-dated cores covering the last ∼10,000 years from six lakes close to Sisimiut (SW Greenland) are used to determine the extent to which OC dynamics reflect climate relative to lake or catchment characteristics. Sediment δ13C ranges from −19 to −32‰ across all lakes, while C/N ratios are <8 to >20 (mean = 12), values that indicate a high proportion of the organic matter is from autochthonous production but with a variable terrestrial component. Temporal trends in δ13C are variable among lakes, with neighbouring lakes showing contrasting profiles, indicative of site-specific OC processing. The response of an individual lake reflects its morphometry (which influences benthic primary production), the catchment:lake ratio, and catchment relief, lakes with steeper catchments sequester more carbon. The multi-site, landscape approach used here highlights the complex response of individual lakes to climate and catchment disturbance, but broad generalisations are possible. Regional Neoglacial cooling (from ∼5000 cal yr BP) influenced the lateral transfer of terrestrial OC to lakes, with three lakes showing clear increases in OC accumulation rate. The lakes likely switched from being autotrophic (i.e. net ecosystem production > ecosystem respiration) in the early Holocene to being heterotrophic after 5000 cal yr BP as terrestrial OC transfer increased.}, journal={Quaternary Science Reviews}, publisher={Elsevier BV}, author={Anderson, N.J. and Leng, M.J. and Osburn, C.L. and Fritz, S.C. and Law, A.C. and McGowan, S.}, year={2018}, month={Dec}, pages={98–108} } @article{kinsey_corradino_ziervogel_schnetzer_osburn_2018, title={Formation of Chromophoric Dissolved Organic Matter by Bacterial Degradation of Phytoplankton-Derived Aggregates}, volume={4}, ISSN={2296-7745}, url={http://dx.doi.org/10.3389/fmars.2017.00430}, DOI={10.3389/fmars.2017.00430}, abstractNote={Organic matter produced and released by phytoplankton during growth is processed by heterotrophic bacterial communities that transform dissolved organic matter into biomass and recycle inorganic nutrients, fueling microbial food web interactions. Bacterial transformation of phytoplankton-derived organic matter also plays a poorly known role in the formation of chromophoric dissolved organic matter (CDOM) which is ubiquitous in the ocean. Despite the importance of organic matter cycling, growth of phytoplankton and activities of heterotrophic bacterial communities are rarely measured in concert. To investigate CDOM formation mediated by microbial processing of phytoplankton-derived aggregates, we conducted growth experiments with non-axenic monocultures of three diatoms (Skeletonema grethae, Leptocylindrus hargravesii, Coscinodiscus sp.) and one haptophyte (Phaeocystis globosa). Phytoplankton biomass, carbon concentrations, CDOM and base-extracted particulate organic matter (BEPOM) fluorescence, along with bacterial abundance and hydrolytic enzyme activities (α-glucosidase, β-glucosidase, leucine-aminopeptidase) were measured during exponential growth and stationary phase (~3-6 weeks) and following six weeks of POM degradation. Incubations were performed in rotating glass bottles to keep cells suspended, promoting cell coagulation and, thus, formation of macroscopic aggregates (marine snow), more similar to surface ocean processes. Maximum carbon concentrations, enzyme activities, and BEPOM fluorescence occurred during stationary phase. Net DOC concentrations (0.19-0.46 mg C L-1) increased on the same order as open ocean concentrations. CDOM fluorescence was dominated by protein-like signals that increased throughout growth and degradation becoming increasingly humic-like, implying the production of more complex molecules from planktonic-precursors mediated by microbial processing. Our experimental results suggest that at least a portion of open-ocean CDOM is produced by autochthonous processes and aggregation likely facilitates microbial reprocessing of organic matter into refractory DOM.}, journal={Frontiers in Marine Science}, publisher={Frontiers Media SA}, author={Kinsey, Joanna D. and Corradino, Gabrielle and Ziervogel, Kai and Schnetzer, Astrid and Osburn, Christopher L.}, year={2018}, month={Jan} } @article{osburn_kinsey_bianchi_shields_2019, title={Formation of planktonic chromophoric dissolved organic matter in the ocean}, volume={209}, ISSN={0304-4203}, url={http://dx.doi.org/10.1016/j.marchem.2018.11.010}, DOI={10.1016/j.marchem.2018.11.010}, abstractNote={Chromophoric dissolved organic matter (CDOM) is an important fraction of the marine carbon cycle that controls most light absorption and many photochemical and biological processes in the ocean. Despite its importance, the chemical basis for the formation of oceanic CDOM remains unclear. Currently, CDOM's optical properties are best-described by an electronic interaction (EI) model of charge transfer (CT) complexes which form between electron-rich donors and electron-poor acceptors. While terrigenous compounds such as lignin best fit this model, planktonic sources of CDOM have not yet been tested. Here, we have tested CDOM formed during an incubation experiment using a natural phytoplankton assemblage and throughout active growth, stationary phase and algal biomass decomposition. Absorbance of the derived planktonic CDOM generally decreased with increasing wavelength, similar to the reference Pony Lake (PLFA) and Suwanee River (SRFA) fulvic acid solutions used as models of terrigenous CDOM. Further, after 60 d of microbial degradation in the dark, CDOM exhibited fluorescence emission maxima continuously red-shifted into the visible band, consistent with PLFA and SRFA. Reduction of carbonyl-containing groups, key to CT complex formation, with sodium borohydride (NaBH4) produced coherent results in planktonic CDOM and reference FAs. Absorption at 350 nm decreased by 50% for planktonic CDOM and by 30% for PLFA and SRFA, with corresponding increases in spectral slope (S) values, indicating preferential loss of absorption well into the visible. Fluorescence likewise responded with enhanced emission at shorter wavelengths. Apparent quantum yields (Φ) were similarly affected. Results from our work support prior observations that phytoplankton and bacteria are important sources of CDOM that color the ocean's “twilight zone”. We hypothesize that microbial processing of a variety of source substrates into more complex compounds represented as planktonic CDOM likely represents a semi-refractory pool of DOM in the ocean.}, journal={Marine Chemistry}, publisher={Elsevier BV}, author={Osburn, Christopher L. and Kinsey, Joanna D. and Bianchi, Thomas S. and Shields, Michael R.}, year={2019}, month={Feb}, pages={1–13} } @article{lee_osburn_shin_hur_2018, title={New insight into the applicability of spectroscopic indices for dissolved organic matter (DOM) source discrimination in aquatic systems affected by biogeochemical processes}, volume={147}, ISSN={["1879-2448"]}, DOI={10.1016/j.watres.2018.09.048}, abstractNote={Despite numerous studies on changes to optical proxies of dissolved organic matter (DOM) by biogeochemical processing, the applicability of commonly-used spectroscopic indices has not been explored as DOM source tracking tools under conditions where biogeochemical processes may alter them. For this study, two contrasting DOM end members, Suwannee River fulvic acid (SRFA) and algogenic DOM (ADOM), and their mixtures, were used to examine the potential changes in the conservative mixing behaviors of several well-known optical indices via end member mixing analysis under the influence of biodegradation, UV irradiation, and clay mineral (kaolin) adsorption. Most of the source tracking indices exhibited large deviations from conservative mixing behavior between the two end-members. Biodegradation tended to lower the portions of labile and ADOM in the mixtures, while the allochthonous end member (SRFA) was reduced by a greater extent after the process of UV irradiation or adsorption. The extent of the variations in biological index (BIX) and fluorescence index (FI) was smaller for more allochthonous DOM mixtures under the processes of biodegradation and UV irradiation. Overall, the process-driven variations in ratios of humic-like: protein-like fluorescence (as modeled by parallel factor analysis, PARAFAC) were greater for the SRFA versus ADOM. Evaluation criteria used in this study suggested that BIX, specific UV absorbance (SUVA), and FI each could be the reliable discrimination parameter least affected by biodegradation, UV irradiation, and adsorption, respectively. This study provided criterion information for the choice and the interpretation of the optical indices for DOM source discrimination in aquatic environments after substantial biogeochemical processing.}, journal={WATER RESEARCH}, author={Lee, Mi-Hee and Osburn, Christopher L. and Shin, Kyung-Hoon and Hur, Jin}, year={2018}, month={Dec}, pages={164–176} } @article{osburn_oviedo-vargas_barnett_dierick_oberbauer_genereux_2018, title={Regional Groundwater and Storms Are Hydrologic Controls on the Quality and Export of Dissolved Organic Matter in Two Tropical Rainforest Streams, Costa Rica}, volume={123}, ISSN={2169-8953}, url={http://dx.doi.org/10.1002/2017JG003960}, DOI={10.1002/2017jg003960}, abstractNote={AbstractA paired‐watershed approach was used to compare the quality and fluxes of dissolved organic matter (DOM) during stormflow and baseflow in two lowland tropical rainforest streams located in northeastern Costa Rica. The Arboleda stream received regional groundwater (RGW) flow, whereas the Taconazo stream did not. DOM quality was assessed with absorbance and fluorescence and stable carbon isotope (δ13C‐DOC) values. RGW DOM lacked detectable fluorescence and had specific ultraviolet absorption (SUVA254) and absorbance slope ratio (SR) values consistent with low aromaticity and low molecular weight material, respectively. We attributed these properties to microbial degradation and sorption of humic DOM to mineral surfaces during transport through bedrock. SUVA254 values were lower and SR values were higher in the Arboleda stream during baseflow compared to the Taconazo stream, presumably due to dilution by RGW. However, no significant difference in SUVA254 or SR occurred between the streams during stormflow. SUVA254 was negatively correlated to δ13C‐DOC (r2 = 0.61, P < 0.001), demonstrating a strong linkage between stream DOM characteristics and the relative amounts of RGW flow and local watershed runoff containing soil and throughfall C sources. Mean DOC export from the Taconazo stream during the study period was 2.62 ± 0.39 g C m−2 year−1, consistent with other tropical streams, yet mean DOC export from the Arboleda stream was 13.79 ± 2.07 g C m−2 year−1, one of the highest exports reported and demonstrating a substantial impact of old RGW from outside the watershed boundary can have on surface water carbon cycling.}, number={3}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Osburn, Christopher L. and Oviedo-Vargas, Diana and Barnett, Emily and Dierick, Diego and Oberbauer, Steven F. and Genereux, David P.}, year={2018}, month={Mar}, pages={850–866} } @article{joshi_ward_d'sa_osburn_bianchi_oviedo-vargas_2018, title={Seasonal Trends in Surface pCO2 and Air-Sea CO2 Fluxes in Apalachicola Bay, Florida, From VIIRS Ocean Color}, volume={123}, ISSN={2169-8953}, url={http://dx.doi.org/10.1029/2018JG004391}, DOI={10.1029/2018JG004391}, abstractNote={AbstractEstuaries have been recognized as important sources of carbon dioxide (CO2) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO2 distribution and air‐sea CO2 fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH‐pCO2 relationships for obtaining surface pCO2 estimates and air‐sea CO2 fluxes from Visible and Infrared Imaging Radiometer Suite (VIIRS) ocean color data. Monthly and seasonal maps of pCO2 and air‐sea CO2 fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO2 fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO2 with large seasonal and spatial variability and a mean annual CO2 flux to the atmosphere of 3.4 ± 3.1 mol·m−2·year−1 (9.4 ± 8.5 mmol·m−2·day−1), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates.}, number={8}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Joshi, Ishan D. and Ward, Nicholas D. and D'Sa, Eurico J. and Osburn, Christopher L. and Bianchi, Thomas S. and Oviedo-Vargas, Diana}, year={2018}, month={Aug}, pages={2466–2484} } @article{fowler_saros_osburn_2018, title={Shifting DOC concentration and quality in the freshwater lakes of the Kangerlussuaq region: An experimental assessment of possible mechanisms}, volume={50}, ISSN={["1938-4246"]}, url={https://doi.org/10.1080/15230430.2018.1436815}, DOI={10.1080/15230430.2018.1436815}, abstractNote={ABSTRACT Since 2003, concentrations of dissolved organic carbon (DOC) in lakes in the Kangerlussuaq region declined by 14–55 percent, with these decreasing DOC concentrations potentially altering lake ecology and reflecting changes in regional carbon (C) cycling. To evaluate possible mechanisms responsible for this shift, we performed experiments to test the effects of dust addition, bacterial activity, or photodegradation on DOC concentration and two DOC quality metrics: the specific ultraviolet absorbance (SUVA254) and the chromophoric DOC spectral slope coefficient (S275–295). Lake-water DOC concentrations did not decline in any treatments, but there were changes in DOC quality. Dust addition increased SUVA254 and decreased the magnitude of S275–295 in one lake, the impacts of bacterial activity were variable, and sunlight exposure elicited a decline in SUVA254 and an increase in the magnitude of S275–295 in all lakes. These results suggest that DOC pools in the study lakes are photoreactive, even though the lakes are characterized by long residence times, but that declining DOC concentration did not result from this mechanism. While the tested mechanisms did not explain the decline in DOC concentration observed in recent years, they did yield new information about how dust, bacterial activity, or light can influence DOC quality in the lakes of the Kangerlussuaq region.}, number={1}, journal={ARCTIC ANTARCTIC AND ALPINE RESEARCH}, publisher={Informa UK Limited}, author={Fowler, Rachel A. and Saros, Jasmine E. and Osburn, Christopher L.}, year={2018}, month={May} } @inbook{bianchi_morrison_barry_arellano_feagin_hinson_eriksson_allison_osburn_oviedo-vargas_2018, title={The Fate and Transport of Allochthonous Blue Carbon in Divergent Coastal Systems}, ISBN={9780429435362}, url={http://dx.doi.org/10.1201/9780429435362-4}, DOI={10.1201/9780429435362-4}, abstractNote={This chapter discusses the fate of allochthonous particulate organic carbon (C) (POC), either sorbed organic C (OC) onto clay particles, as detrital organic particles, and dissolved OC (DOC) in modern coastal blue C ecosystem (BCE). BCEs, or the C stored in coastal systems such as mangroves, salt marshes, and seagrass meadows, form some of the largest global C reserves, and are distributed throughout numerous latitudinal zones. Coastal tidal marshes are largely found in temperate zones but do extend into the tropics, mangroves are confined to tropical and sub-tropical regions due to their freeze intolerance, and seagrasses are broadly distributed from cold polar waters to the tropics. The fate of allochthonous blue C released into coastal waters and the open sea or sequestered in the coastal BCEs is highly specific to the coastal margin setting. Coastal aqueous POC and DOC forms constitute the major pool of organic matter providing C and energy to heterotrophs in estuaries.}, booktitle={A Blue Carbon Primer}, publisher={CRC Press}, author={Bianchi, Thomas S. and Morrison, Elise and Barry, Savanna and Arellano, Ana R. and Feagin, Rusty A. and Hinson, Audra and Eriksson, Marian and Allison, Mead and Osburn, Christopher L. and Oviedo-Vargas, Diana}, year={2018}, month={Nov}, pages={27–49} } @article{paerl_crosswell_van dam_hall_rossignol_osburn_hounshell_sloup_harding_2018, title={Two decades of tropical cyclone impacts on North Carolina’s estuarine carbon, nutrient and phytoplankton dynamics: implications for biogeochemical cycling and water quality in a stormier world}, volume={141}, ISSN={0168-2563 1573-515X}, url={http://dx.doi.org/10.1007/s10533-018-0438-x}, DOI={10.1007/s10533-018-0438-x}, abstractNote={Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on biogeochemical cycling and phytoplankton responses in a large estuarine complex, the Pamlico Sound (PS) and Neuse River Estuary (NRE). Major storms caused up to a doubling of annual nitrogen and tripling of phosphorus loading compared to non-storm years; magnitudes of loading depended on storm tracks, forward speed, and precipitation in NRE-PS watersheds. With regard to C cycling, NRE-PS was a sink for atmospheric CO2 during dry, storm-free years and a significant source of CO2 in years with at least one storm, although responses were storm-specific. Hurricane Irene (2011) mobilized large amounts of previously-accumulated terrigenous C in the watershed, mainly as dissolved organic carbon, and extreme winds rapidly released CO2 to the atmosphere. Historic flooding after Hurricanes Joaquin (2015) and Matthew (2016) provided large inputs of C from the watershed, modifying the annual C balance of NRE-PS and leading to sustained CO2 efflux for months. Storm type affected biogeochemical responses as C-enriched floodwaters enhanced air–water CO2 exchange during ‘wet’ storms, while CO2 fluxes during ‘windy’ storms were largely supported by previously-accumulated C. Nutrient loading and flushing jointly influenced spatio-temporal patterns of phytoplankton biomass and composition. These findings suggest the importance of incorporating freshwater discharge and C dynamics in nutrient management strategies for coastal ecosystems likely to experience a stormier future.}, number={3}, journal={Biogeochemistry}, publisher={Springer Science and Business Media LLC}, author={Paerl, Hans W. and Crosswell, Joseph R. and Van Dam, Bryce and Hall, Nathan S. and Rossignol, Karen L. and Osburn, Christopher L. and Hounshell, Alexandria G. and Sloup, Randolph S. and Harding, Lawrence W.}, year={2018}, month={Mar}, pages={307–332} } @article{mitra_osburn_wozniak_2017, title={A Preliminary Assessment of Fossil Fuel and Terrigenous Influences to Rainwater Organic Matter in Summertime in the Northern Gulf of Mexico}, volume={23}, ISSN={["1573-1421"]}, DOI={10.1007/s10498-017-9319-5}, number={4}, journal={AQUATIC GEOCHEMISTRY}, author={Mitra, Siddhartha and Osburn, Christopher L. and Wozniak, Andrew S.}, year={2017}, month={Aug}, pages={217–231} } @article{joshi_eurico j. d'sa_osburn_bianchi_ko_oviedo-vargas_arellano_ward_2017, title={Assessing chromophoric dissolved organic matter (CDOM) distribution, stocks, and fluxes in Apalachicola Bay using combined field, VIIRS ocean color, and model observations}, volume={191}, ISSN={["1879-0704"]}, DOI={10.1016/j.rse.2017.01.039}, abstractNote={Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. The chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412 nm (ag412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processes using satellite ocean color imagery necessitates the removal of atmospheric contribution (~ 90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R2 = 0.95, N = 25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R2 = 0.87, N = 9) and validated (R2 = 0.76, N = 20, RMSE = 0.29 m− 1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC = 1.08 + 0.94 × ag412, R2 = 0.88, N = 13) and in November (DOC = 1.61 + 1.33 × ag412, R2 = 0.83, N = 24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~ 3.71 × 106 kg C in March and ~ 4.07 × 106 kg C in November over an area of ~ 560 km2. Volume flux (out of the bay) almost doubled for March 24 (735 m3 s− 1) relative to November 4 (378 m3 s− 1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163 × 106 kg C d− 1) than in November (0.124 × 106 kg C d− 1) and reflected greater DOC stocks in the fall. The combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.}, journal={REMOTE SENSING OF ENVIRONMENT}, author={Joshi, Ishan D. and Eurico J. D'Sa and Osburn, Christopher L. and Bianchi, Thomas S. and Ko, Dong S. and Oviedo-Vargas, Diana and Arellano, Ana R. and Ward, Nicholas D.}, year={2017}, month={Mar}, pages={359–372} } @article{bhattacharya_osburn_2017, title={Multivariate Analyses of Phytoplankton Pigment Fluorescence from a Freshwater River Network}, volume={51}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/acs.est.6b05880}, DOI={10.1021/acs.est.6b05880}, abstractNote={Monitoring phytoplankton classes in river networks is critical to understanding phytoplankton dynamics and to predicting the ecosystem response to changing land-use and seasons. Applicability of phytoplankton fluorescence as a quick and effective ecological monitoring approach is relatively unexplored in freshwater ecosystems. We used multivariate analyses of fluorescence from pigment extracted in 90% acetone to assess the variability in phytoplankton classes, herbivory, and organic matter quality in a freshwater river network. A total of four models developed by the parallel factor analysis (PARAFAC) of fluorescence excitation and emission matrices identified six components: Model 1 (pheophytin-A and chlorophyll-A), Model 2 (chlorophyll-B and chlorophyll-C), Model 3 (pheophytin-B), and Model 4 (pheophytin-C). Redundancy analyses revealed that in the summer, urban and agricultural streams were abundant in chlorophylls, fresh organic matter, and organic nitrogen, whereas in winter, streams were high in phaeopigments. A slow-moving, light-limited wetland stream was an exception as high phaeopigment abundance was observed in both seasons. The PARAFAC components were used to develop a partial least-squares regression-based model (r2 = 0.53; Nash-Sutcliffe efficiency = 0.5; n = 147) that successfully predicted chlorophyll-A concentrations from an external subset of river water samples (r2 = 0.41; p < 0.0001; n = 75). Thus, combining multivariate analyses and fluorescence spectroscopy is useful for monitoring and predicting phytoplankton dynamics in large river networks.}, number={12}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Bhattacharya, Ruchi and Osburn, Christopher L.}, year={2017}, month={May}, pages={6683–6690} } @article{osburn_anderson_stedmon_giles_whiteford_mcgenity_dumbrell_underwood_2017, title={Shifts in the Source and Composition of Dissolved Organic Matter in Southwest Greenland Lakes Along a Regional Hydro-climatic Gradient}, volume={122}, ISSN={2169-8953}, url={http://dx.doi.org/10.1002/2017JG003999}, DOI={10.1002/2017jg003999}, abstractNote={AbstractDissolved organic matter (DOM) concentration and quality were examined from Arctic lakes located in three clusters across south‐west (SW) Greenland, covering the regional climatic gradient: cool, wet coastal zone; dry inland interior; and cool, dry ice‐marginal areas. We hypothesized that differences in mean annual precipitation between sites would result in a reduced hydrological connectivity between lakes and their catchments and that this concentrates degraded DOM. The DOM in the inland lake group was characterized by a lower aromaticity and molecular weight, a low soil‐like fluorescence, and carbon stable isotope (δ13C‐DOC) values enriched by ~2‰ relative to the coastal group. DOC‐specific absorbance (SUVA254) and DOC‐specific soil‐like fluorescence (SUVFC1) revealed seasonal and climatic gradients across which DOM exhibited a dynamic we term “pulse‐process”: Pulses of DOM exported from soils to lakes during snow and ice melt were followed by pulses of autochthonous DOM inputs (possibly from macrophytes), and their subsequent photochemical and microbial processing. These effects regulated the dynamics of DOM in the inland lakes and suggested that if circumpolar lakes currently situated in cool wetter climatic regimes with strong hydrological connectivity have reduced connectivity under a drier future climate, they may evolve toward an end‐point of large stocks of highly degraded DOC, equivalent to the inland lakes in the present study. The regional climatic gradient across SW Greenland and its influence on DOM properties in these lakes provide a model of possible future changes to lake C cycling in high‐latitude systems where climatic changes are most pronounced.}, number={12}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Osburn, Christopher L. and Anderson, Nicholas J. and Stedmon, Colin A. and Giles, Madeline E. and Whiteford, Erika J. and McGenity, Terry J. and Dumbrell, Alex J. and Underwood, Graham J. C.}, year={2017}, month={Dec}, pages={3431–3445} } @article{hounshell_peierls_osburn_paerl_2017, title={Stimulation of Phytoplankton Production by Anthropogenic Dissolved Organic Nitrogen in a Coastal Plain Estuary}, volume={51}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.7b03538}, abstractNote={There is increased focus on nitrogen (N)-containing dissolved organic matter (DOM) as a nutrient source supporting eutrophication in N-sensitive estuarine ecosystems. This is particularly relevant in watersheds undergoing urban and agricultural development, leading to increased dissolved organic N (DON) loading. To understand how this shift in N-loading influences estuarine phytoplankton production, nutrient addition bioassays were conducted in the N-limited Neuse River Estuary, North Carolina from 2014 to 2015. Additions included N-rich DOM sources characteristic of urban and agricultural development, including chicken and turkey litter leachate, wastewater treatment facility effluent, and concentrated river DOM (used as a reference). Each DOM addition was coupled with an inorganic nutrient treatment to account for inorganic nutrient concentrations (NO2/3, NH4, PO4) in each respective DOM addition. Repeated measures analysis of variance (RM-ANOVA) showed that chicken litter leachate stimulated phytoplankton growth greater than its coupled inorganic nutrient treatment. Wastewater treatment facility effluent, turkey litter leachate, and concentrated river DOM did not stimulate phytoplankton growth greater than their respective inorganic nutrient controls. DOM fluorescence (EEM-PARAFAC) indicated the chicken litter contained a biologically reactive fluorescent DOM component, identified as the nonhumic, biologically labile, "N-peak", which may be responsible for stimulating the observed phytoplankton growth in the chicken litter leachate treatments.}, number={22}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Hounshell, Alexandria G. and Peierls, Benjamin L. and Osburn, Christopher L. and Paerl, Hans W.}, year={2017}, month={Nov}, pages={13104–13112} } @book{montgomery_boyd_osburn_2017, place={Washington, DC}, title={TNT Degradation by Natural Microbial Assemblages at Frontal Boundaries Between Water Masses in Coastal Ecosystems (ER-2124)}, url={https://apps.dtic.mil/dtic/tr/fulltext/u2/1038774.pdf}, number={NRL/MR/6110--17-9740}, institution={Chemical Dynamics and Diagnostics Branch, Naval Research Lab}, author={Montgomery, Michael and Boyd, Thomas and Osburn, Christopher}, year={2017}, month={Jun} } @article{joshi_eurico j. d'sa_osburn_bianchi_2017, title={Turbidity in Apalachicola Bay, Florida from Landsat 5 TM and Field Data: Seasonal Patterns and Response to Extreme Events}, volume={9}, ISSN={["2072-4292"]}, DOI={10.3390/rs9040367}, abstractNote={Synoptic monitoring of estuaries, some of the most bio-diverse and productive environments on Earth, is essential to study small-scale water dynamics and its role on spatiotemporal variation in water quality important to indigenous marine species and surrounding human settlements. We present a detailed study of turbidity, an optical index of water quality, in Apalachicola Bay, Florida (USA) using historical in situ measurements and Landsat 5 TM data archive acquired from 2004 to 2011. Data mining techniques such as time-series decomposition, principal component analysis, and classification tree-based models were utilized to decipher time-series for examining variations in physical forcings, and their effects on diurnal and seasonal variability in turbidity in Apalachicola Bay. Statistical analysis showed that the bay is highly dynamic in nature, both diurnally and seasonally, and its water quality (e.g., turbidity) is largely driven by interactions of different physical forcings such as river discharge, wind speed, tides, and precipitation. River discharge and wind speed are the most influential forcings on the eastern side of river mouth, whereas all physical forcings were relatively important to the western side close to the major inlet, the West Pass. A bootstrap-optimized and atmospheric-corrected single-band empirical relationship (Turbidity (NTU) = 6568.23 × (Reflectance (Band 3))1.95; R2 = 0.77 ± 0.06, range = 0.50–0.91, N = 50) is proposed with seasonal thresholds for its application in various seasons. The validation of this relationship yielded R2 = 0.70 ± 0.15 (range = −0.96–0.97; N = 38; RMSE = 7.78 ± 2.59 NTU; Bias (%) = −8.70 ± 11.48). Complex interactions of physical forcings and their effects on water dynamics have been discussed in detail using Landsat 5 TM-based turbidity maps during major events between 2004 and 2011. Promising results of the single-band turbidity algorithm with Landsat 8 OLI imagery suggest its potential for long-term monitoring of water turbidity in a shallow water estuary such as Apalachicola Bay.}, number={4}, journal={REMOTE SENSING}, author={Joshi, Ishan D. and Eurico J. D'Sa and Osburn, Christopher L. and Bianchi, Thomas S.}, year={2017}, month={Apr} } @article{osburn_bianchi_2016, title={Editorial: Linking Optical and Chemical Properties of Dissolved Organic Matter in Natural Waters}, volume={3}, ISSN={2296-7745}, url={http://dx.doi.org/10.3389/fmars.2016.00223}, DOI={10.3389/fmars.2016.00223}, abstractNote={EDITORIAL article Front. Mar. Sci., 16 November 2016Sec. Marine Biogeochemistry Volume 3 - 2016 | https://doi.org/10.3389/fmars.2016.00223}, journal={Frontiers in Marine Science}, publisher={Frontiers Media SA}, author={Osburn, Christopher L. and Bianchi, Thomas S.}, year={2016}, month={Nov} } @article{ziervogel_osburn_brym_battles_joye_d'souza_montoya_passow_arnosti_2016, title={Linking Heterotrophic Microbial Activities with Particle Characteristics in Waters of the Mississippi River Delta in the Aftermath of Hurricane Isaac}, volume={3}, ISSN={2296-7745}, url={http://dx.doi.org/10.3389/fmars.2016.00008}, DOI={10.3389/fmars.2016.00008}, abstractNote={Riverine runoff often triggers microbial responses in coastal marine environments, including phytoplankton blooms and enhanced bacterial biomass production that drive the transformation of dissolved and particulate organic matter on its way from land to the deep ocean. We measured concentrations and characteristics of particulate organic matter (POM), concentrations of dissolved organic carbon (DOC), and bacterial community abundance and activities in the water column at three sites near the Mississippi River Delta two weeks after Hurricane Isaac made landfall in late August 2012. River plumes had salinities of >30 PSU and high levels of DOC (210-380 µM), resulting from the storm surge that pushed large quantities of marine waters upstream. Relatively high concentrations of phytoplankton POM and low levels of microbial exopolymeric particles (TEP and CSP) suggested that storm-induced riverine discharge triggered the development of phytoplankton blooms that were in their initial stages at the time of sampling. Surface water POM had C/N ratios of 5-7 and strong protein-like fluorescence signals in the base-extracted POM (BEPOM) fraction at the two sites closer to the river mouth (Stns. TE and MSP). Freshly produced POM triggered a twofold increase in heterotrophic bacterial biomass production (3H-leucine incorporation) and a fourfold increase in bacterial peptide hydrolysis (activities of leucine-aminopeptidase). In contrast, elevated DOC concentrations coincided with only moderate bacterial community activity, suggesting that heterotrophic bacterial metabolism near the Mississippi River Delta in the aftermath of Hurricane Isaac was more closely linked with autochthonous primary production.}, journal={Frontiers in Marine Science}, publisher={Frontiers Media SA}, author={Ziervogel, Kai and Osburn, Christopher and Brym, Adeline and Battles, Jessica and Joye, Samantha and D'souza, Nigel and Montoya, Joseph and Passow, Uta and Arnosti, Carol}, year={2016}, month={Feb} } @article{schnetzer_lampe_benitez-nelson_marchetti_osburn_tatters_2017, title={Marine snow formation by the toxin-producing diatom, Pseudo-nitzschia australis}, volume={61}, ISSN={["1878-1470"]}, DOI={10.1016/j.hal.2016.11.008}, abstractNote={The formation of marine snow (MS) by the toxic diatom Pseudo-nitschia australis was simulated using a roller table experiment. Concentrations of particulate and dissolved domoic acid (pDA and dDA) differed significantly among exponential phase and MS formation under simulated near surface conditions (16 °C/12:12-dark:light cycle) and also differed compared to subsequent particle decomposition at 4 °C in the dark, mimicking conditions in deeper waters. Particulate DA was first detected at the onset of exponential growth, reached maximum levels associated with MS aggregates (1.21 ± 0.24 ng mL−1) and declined at an average loss rate of ∼1.2% pDA day−1 during particle decomposition. Dissolved DA concentrations increased throughout the experiment and reached a maximum of ∼20 ng mL−1 at final sampling on day 88. The succession by P. australis from active growth to aggregation resulted in increasing MS toxicity and based on DA loading of particles and known in situ sinking speeds, a significant amount of toxin could have easily reached the deeper ocean or seafloor. MS formation was further associated with significant dDA accumulation at a ratio of pDA: dDA: cumulative dDA of approximately 1:10:100. Overall, this study confirms that MS functions as a major vector for toxin flux to depth, that Pseudo-nitzschia-derived aggregates should be considered 'toxic snow' for MS-associated organisms, and that effects of MS toxicity on interactions with aggregate-associated microbes and zooplankton consumers warrant further consideration.}, journal={HARMFUL ALGAE}, author={Schnetzer, Astrid and Lampe, Robert H. and Benitez-Nelson, Claudia R. and Marchetti, Adrian and Osburn, Christopher L. and Tatters, Avery O.}, year={2017}, month={Jan}, pages={23–30} } @article{osburn_boyd_montgomery_bianchi_coffin_paerl_2016, title={Optical Proxies for Terrestrial Dissolved Organic Matter in Estuaries and Coastal Waters}, volume={2}, ISSN={2296-7745}, url={http://dx.doi.org/10.3389/fmars.2015.00127}, DOI={10.3389/fmars.2015.00127}, abstractNote={Optical proxies, especially DOM fluorescence, were used to track terrestrial DOM fluxes through estuaries and coastal waters by comparing models developed for several coastal ecosystems. Key to using optical properties is validating and calibrating them with chemical measurements, such as lignin-derived phenols - a proxy to quantify terrestrial DOM. Utilizing parallel factor analysis (PARAFAC), and comparing models statistically using the OpenFluor database (http://www.openfluor.org) we have found common, ubiquitous fluorescing components which correlate most strongly with lignin phenol concentrations in several estuarine and coastal environments. Optical proxies for lignin were computed for the following regions: Mackenzie River Estuary, Atchafalaya River Estuary, Charleston Harbor, Chesapeake Bay, and Neuse River Estuary. The slope of linear regression models relating CDOM absorption at 350 nm (a350) to DOC and to lignin, varied 5 to 10 fold among systems. Where seasonal observations were available from a region, there were distinct seasonal differences in equation parameters for these optical proxies. Despite variability, overall models using single linear regression were developed that related dissolved organic carbon (DOC) concentration to CDOM (DOC = 40×a350+138; R2 = 0.77; N = 130) and lignin (Σ8) to CDOM (Σ8 = 2.03×a350-0.5; R2 = 0.87; N = 130). This wide variability suggested that local or regional optical models should be developed for predicting terrestrial DOM flux into coastal oceans and taken into account when upscaling to remote sensing observations and calibrations.}, journal={Frontiers in Marine Science}, publisher={Frontiers Media SA}, author={Osburn, Christopher L. and Boyd, Thomas J. and Montgomery, Michael T. and Bianchi, Thomas S. and Coffin, Richard B. and Paerl, Hans W.}, year={2016}, month={Jan} } @article{osburn_handsel_peierls_paerl_2016, title={Predicting Sources of Dissolved Organic Nitrogen to an Estuary from an Agro-Urban Coastal Watershed}, volume={50}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/acs.est.6b00053}, DOI={10.1021/acs.est.6b00053}, abstractNote={Dissolved organic nitrogen (DON) is the nitrogen (N)-containing component of dissolved organic matter (DOM) and in aquatic ecosystems is part of the biologically reactive nitrogen pool that can degrade water quality in N-sensitive waters. Unlike inorganic N (nitrate and ammonium) DON is comprised of many different molecules of variable reactivity. Few methods exist to track the sources of DON in watersheds. In this study, DOM excitation-emission matrix (EEM) fluorescence of eight discrete DON sources was measured and modeled with parallel factor analysis (PARAFAC) and the resulting model ("FluorMod") was fit to 516 EEMs measured in surface waters from the main stem of the Neuse River and its tributaries, located in eastern North Carolina. PARAFAC components were positively correlated to DON concentration. Principle components analysis (PCA) was used to confirm separation of the eight sources and model validation was achieved by measurement of source samples not included in the model development with an error of <10%. Application of FluorMod to surface waters of streams within the Neuse River Basin showed that while >70% of DON was attributed to natural sources, nonpoint sources, such as soil and poultry litter leachates and street runoff, accounted for the remaining 30%. This result was consistent with changes in land use from urbanized Raleigh metropolitan area to the largely agricultural Southeastern coastal plain. Overall, the predicted fraction of nonpoint DON sources was consistent with previous reports of increased organic N inputs in this river basin, which are suspected of impacting the water quality of its estuary.}, number={16}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Osburn, Christopher L. and Handsel, Lauren T. and Peierls, Benjamin L. and Paerl, Hans W.}, year={2016}, month={Jul}, pages={8473–8484} } @article{anderson_saros_bullard_cahoon_mcgowan_bagshaw_barry_bindler_burpee_carrivick_et al._2017, title={The Arctic in the Twenty-First Century: Changing Biogeochemical Linkages across a Paraglacial Landscape of Greenland}, volume={67}, ISSN={0006-3568 1525-3244}, url={http://dx.doi.org/10.1093/biosci/biw158}, DOI={10.1093/biosci/biw158}, abstractNote={Abstract The Kangerlussuaq area of southwest Greenland encompasses diverse ecological, geomorphic, and climate gradients that function over a range of spatial and temporal scales. Ecosystems range from the microbial communities on the ice sheet and moisture‐stressed terrestrial vegetation (and their associated herbivores) to freshwater and oligosaline lakes. These ecosystems are linked by a dynamic glacio‐fluvial‐aeolian geomorphic system that transports water, geological material, organic carbon and nutrients from the glacier surface to adjacent terrestrial and aquatic systems. This paraglacial system is now subject to substantial change because of rapid regional warming since 2000. Here, we describe changes in the eco‐ and geomorphic systems at a range of timescales and explore rapid future change in the links that integrate these systems. We highlight the importance of cross‐system subsidies at the landscape scale and, importantly, how these might change in the near future as the Arctic is expected to continue to warm.}, number={2}, journal={BioScience}, publisher={Oxford University Press (OUP)}, author={Anderson, N. John and Saros, Jasmine E. and Bullard, Joanna E. and Cahoon, Sean M. P. and McGowan, Suzanne and Bagshaw, Elizabeth A. and Barry, Christopher D. and Bindler, Richard and Burpee, Benjamin T. and Carrivick, Jonathan L. and et al.}, year={2017}, month={Feb}, pages={118–133} } @article{saros_northington_osburn_burpee_john anderson_2016, title={Thermal stratification in small arctic lakes of southwest Greenland affected by water transparency and epilimnetic temperatures}, volume={61}, ISSN={0024-3590}, url={http://dx.doi.org/10.1002/lno.10314}, DOI={10.1002/lno.10314}, abstractNote={AbstractWe assessed which factors control summer epilimnion thickness in arctic lakes of southwest Greenland. A suite of 22 lakes that thermally stratify was measured in the summer of 2013; a sub‐set of eight of the lakes was measured again in 2014, which was a warmer summer than 2013. Regression analysis of the 22 lakes indicated that the 1% attenuation depth for photosynthetically active radiation (PAR) was the strongest single predictor (R2 = 0.75) of epilimnion thickness across lakes; the addition of epilimnion temperature to the PAR model explained additional variability (R2 = 0.79). The importance of including temperature in the model was apparent in the results of model validation as well as when comparing across years: while the 1% PAR was 0.4–2 m deeper in 2014 compared with 2013, water temperatures were 2–3°C higher, resulting in July epilimnion thicknesses that were equal to or shallower than in 2013. In these lakes with low color dissolved organic carbon (DOC), multiple factors control the 1% PAR, including absorbance at 440 nm (a440), 380 nm (a380), and 320 (a320), chlorophyll a (Chl a) and DOC concentration. In 2014, when 1% PAR was deeper than in 2013, a380, Chl a and DOC were lower in six of the eight lakes. Our results reveal that the thermal structure of these arctic lakes is under complex control by air temperatures and factors that affect PAR attenuation, particularly Chl a and DOC quality, suggesting that continued warming in the Arctic will have strong effects on lake stratification.}, number={4}, journal={Limnology and Oceanography}, publisher={Wiley}, author={Saros, Jasmine E. and Northington, Robert M. and Osburn, Christopher L. and Burpee, Benjamin T. and John Anderson, Nicholas}, year={2016}, month={May}, pages={1530–1542} } @article{coffin_osburn_plummer_smith_rose_grabowski_2015, title={Deep Sediment-Sourced Methane Contribution to Shallow Sediment Organic Carbon: Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico}, volume={8}, ISSN={["1996-1073"]}, DOI={10.3390/en8031561}, abstractNote={Coastal methane hydrate deposits are globally abundant. There is a need to understand the deep sediment sourced methane energy contribution to shallow sediment carbon relative to terrestrial sources and phytoplankton. Shallow sediment and porewater samples were collected from Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico near a seafloor mound feature identified in geophysical surveys as an elevated bottom seismic reflection. Geochemical data revealed off-mound methane diffusion and active fluid advection on-mound. Gas composition (average methane/ethane ratio ~11,000) and isotope ratios of methane on the mound (average δ 13 C CH4(g) = −71.2‰; D 14 C CH4(g) = −961‰) indicate a deep sediment, microbial source. Depleted sediment organic carbon values on mound (δ 13 C SOC = −25.8‰; D 14 C SOC = −930‰) relative to off-mound (δ 13 C SOC = −22.5‰; D 14 C SOC = −629‰) suggest deep sourced ancient carbon is incorporated into shallow sediment organic matter. Porewater and sediment data indicate inorganic carbon fixed during anaerobic oxidation of methane is a dominant contributor to on-mound shallow sediment organic carbon cycling. A simple stable carbon isotope mass balance suggests carbon fixation of dissolved inorganic carbon (DIC) associated with anaerobic oxidation of hydrate-sourced CH 4 contributes up to 85% of shallow sediment organic carbon.}, number={3}, journal={ENERGIES}, publisher={MDPI AG}, author={Coffin, Richard B. and Osburn, Christopher L. and Plummer, Rebecca E. and Smith, Joseph P. and Rose, Paula S. and Grabowski, Kenneth S.}, year={2015}, month={Mar}, pages={1561–1583} } @article{de la cruz_dittmar_niggemann_osburn_barlaz_2015, title={Evaluation of Copper Oxide Oxidation for Quantification of Lignin in Municipal Solid Waste}, volume={32}, ISSN={1092-8758 1557-9018}, url={http://dx.doi.org/10.1089/ees.2014.0402}, DOI={10.1089/ees.2014.0402}, abstractNote={Abstract The ability to quantify lignin is an important tool for characterizing the extent of decomposition of municipal solid waste (MSW). Traditionally, acid insoluble Klason lignin (KL) has been used to measure lignin. However, synthetic organic materials such as plastics and rubber present in MSW interfere with the traditional KL method, resulting in artificially high measurements. Another method for lignin analysis is CuO oxidation, in which lignin is oxidatively hydrolyzed into phenolic monomers that are quantified by high-performance liquid chromatography or gas chromatography–mass spectrography. The objective of this study was to evaluate the applicability of CuO oxidation to measure the lignin content of MSW. The study demonstrated that analysis of lignin monomers can be simplified by skipping the ethyl acetate extraction step and that ball milling is not necessary to optimize CuO oxidation. Neither the MSW components (e.g., plastics and metals) nor extractives affected CuO oxidation. The ratio o...}, number={6}, journal={Environmental Engineering Science}, publisher={Mary Ann Liebert Inc}, author={De la Cruz, Florentino Banaag and Dittmar, Thorsten and Niggemann, Jutta and Osburn, Christopher L. and Barlaz, Morton A.}, year={2015}, month={Jun}, pages={486–496} } @inbook{zhou_guo_osburn_2015, title={Fluorescence EEMs and PARAFAC Techniques in the Analysis of Petroleum Components in the Water Column}, ISBN={9783662527917 9783662527931}, ISSN={1949-2448 1949-2456}, url={http://dx.doi.org/10.1007/8623_2015_137}, DOI={10.1007/8623_2015_137}, abstractNote={Fluorescence excitation–emission matrix (EEM) techniques coupled with parallel factor (PARAFAC) modeling have been used in the diagnosis and identification of petroleum and hydrocarbon components in aquatic environments. Here, we provide detailed protocols for the use of UV–Vis spectroscopy and fluorescence spectroscopy and for data acquisition and processing. UV absorbance at different wavelengths is used to derive optical properties, such as absorption coefficient at 254 nm (a254), specific UV absorbance (SUVA254), and spectral slopes at different wavelength intervals (e.g., S275–295) or slope ratio, and data of fluorescence EEMs are used to identify major fluorescence components. In addition, SUVA254 and spectral slope values are related to aromaticity and molecular weights of dissolved organic matter (DOM). Oil-related fluorescent components and specific polycyclic aromatic hydrocarbon (PAH) compounds could be readily identified using fluorescence EEMs, especially when combined with PARAFAC analysis. During and after the Deepwater Horizon oil spill in the Gulf of Mexico, three oil components were found in the water column with maximum Ex/Em at 224–226/328–340, 232–244/346–366, and 264–252/311–324 nm, respectively. Major PAH compounds identified include naphthalene, fluorene, phenanthrene, and others. Oil component ratios can also serve as an indicator for oil degradation status. Optical properties especially fluorescence signatures and fluorescence component ratios serve as a complement to other chemical and molecular analyses of petroleum and hydrocarbon components in seawater.}, booktitle={Springer Protocols Handbooks}, publisher={Springer Berlin Heidelberg}, author={Zhou, Zhengzhen and Guo, Laodong and Osburn, Christopher L.}, year={2015}, pages={179–200} } @article{saros_osburn_northington_birkel_auger_stedmon_anderson_2015, title={Recent decrease in DOC concentrations in Arctic lakes of southwest Greenland}, volume={42}, ISSN={["1944-8007"]}, DOI={10.1002/2015gl065075}, abstractNote={AbstractA key indicator of changes in the terrestrial carbon cycle is shifting dissolved organic carbon (DOC) concentrations in surface waters. Arctic permafrost holds twice as much C as the atmosphere, thus recent warming and changes in atmospheric deposition to the region raise the need for a better understanding of how DOC is changing in arctic surface waters. In Kangerlussuaq, Greenland, lakewater DOC concentrations declined by 14 to 55% (absolute changes of 1 to 24 mg L−1) between 2003 and 2013, without significant changes in quality. Lakewater sulfate concentrations, but not chloride or conductivity, increased. These results suggest that similar to processes that have occurred at northern midlatitudes, increases in soil ionic strength as a result of sulfate enrichment may be linked to declining surface water DOC concentrations. Such enrichment may be occurring with enhanced non‐sea‐salt sulfate deposition. Our results reveal that rapid changes are occurring in the carbon cycle of this region of southwest Greenland.}, number={16}, journal={GEOPHYSICAL RESEARCH LETTERS}, publisher={Wiley-Blackwell}, author={Saros, Jasmine E. and Osburn, Christopher L. and Northington, Robert M. and Birkel, Sean D. and Auger, Jeffrey D. and Stedmon, Colin A. and Anderson, Nicholas John}, year={2015}, month={Aug}, pages={6703–6709} } @article{osburn_mikan_etheridge_burchell_birgand_2015, title={Seasonal variation in the quality of dissolved and particulate organic matter exchanged between a salt marsh and its adjacent estuary}, volume={120}, ISSN={2169-8953}, url={http://dx.doi.org/10.1002/2014JG002897}, DOI={10.1002/2014jg002897}, abstractNote={AbstractFluorescence was used to examine the quality of dissolved and particulate organic matter (DOM and POM) exchanging between a tidal creek in a created salt marsh and its adjacent estuary in eastern North Carolina, USA. Samples from the creek were collected hourly over four tidal cycles in May, July, August, and October 2011. Absorbance and fluorescence of chromophoric DOM (CDOM) and of base‐extracted POM (BEPOM) served as the tracers for organic matter quality while dissolved organic carbon (DOC) and base‐extracted particulate organic carbon (BEPOC) were used to compute fluxes. Fluorescence was modeled using parallel factor analysis (PARAFAC) and principle components analysis (PCA) of the PARAFAC results. Of nine PARAFAC components (C) modeled, C3 represented recalcitrant DOM and C4 represented fresher soil‐derived source DOM. Component 1 represented detrital POM, and C6 represented planktonic POM. Based on mass balance, recalcitrant DOC export was 86 g C m−2 yr−1 and labile DOC export was 49 g C m−2 yr−1; no planktonic DOC was exported. The marsh also exported 41 g C m−2 yr−1 of detrital terrestrial POC, which likely originated from lands adjacent to the North River estuary. Planktonic POC export from the marsh was 6 g C m−2 yr−1. Assuming the exported organic matter was oxidized to CO2 and scaled up to global salt marsh area, respiration of salt marsh DOC and POC transported to estuaries could amount to a global CO2 flux of 11 Tg C yr−1, roughly 4% of the recently estimated CO2 release for marshes and estuaries globally.}, number={7}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Osburn, Christopher L. and Mikan, Molly P. and Etheridge, J. Randall and Burchell, Michael R. and Birgand, François}, year={2015}, month={Jul}, pages={1430–1449} } @article{bianchi_osburn_shields_yvon-lewis_young_guo_zhou_2014, title={Deepwater Horizon Oil in Gulf of Mexico Waters after 2 Years: Transformation into the Dissolved Organic Matter Pool}, volume={48}, ISSN={["1520-5851"]}, DOI={10.1021/es501547b}, abstractNote={Recent work has shown the presence of anomalous dissolved organic matter (DOM), with high optical yields, in deep waters 15 months after the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico (GOM). Here, we continue to use the fluorescence excitation-emission matrix (EEM) technique coupled with parallel factor analysis (PARAFAC) modeling, measurements of bulk organic carbon, dissolved inorganic carbon (DIC), oil indices, and other optical properties to examine the chemical evolution and transformation of oil components derived from the DWH in the water column of the GOM. Seawater samples were collected from the GOM during July 2012, 2 years after the oil spill. This study shows that, while dissolved organic carbon (DOC) values have decreased since just after the DWH spill, they remain higher at some stations than typical deep-water values for the GOM. Moreover, we continue to observe fluorescent DOM components in deep waters, similar to those of degraded oil observed in lab and field experiments, which suggest that oil-related fluorescence signatures, as part of the DOM pool, have persisted for 2 years in the deep waters. This supports the notion that some oil-derived chromophoric dissolved organic matter (CDOM) components could still be identified in deep waters after 2 years of degradation, which is further supported by the lower DIC and partial pressure of carbon dioxide (pCO2) associated with greater amounts of these oil-derived components in deep waters, assuming microbial activity on DOM in the current water masses is only the controlling factor of DIC and pCO2 concentrations.}, number={16}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, publisher={American Chemical Society (ACS)}, author={Bianchi, Thomas S. and Osburn, Christopher and Shields, Michael R. and Yvon-Lewis, Shari and Young, Jordan and Guo, Laodong and Zhou, Zhengzhen}, year={2014}, month={Aug}, pages={9288–9297} } @book{giordano_montgomery_osburn_lindsay_2014, place={Washington, DC}, title={Measurement of Nitroaromatic Explosives by Micellar Electrokinetic Chromatography in Waters Collected Along a Tropical Estuary}, url={https://apps.dtic.mil/dtic/tr/fulltext/u2/a595043.pdf}, number={NRL/MR/6110--14-9504}, institution={Chemical Dynamics and Diagnostics Branch, Naval Research Lab}, author={Giordano, B.C. and Montgomery, M.T. and Osburn, C.L. and Lindsay, C.}, year={2014} } @article{brym_paerl_montgomery_handsel_ziervogel_osburn_2014, title={Optical and chemical characterization of base-extracted particulate organic matter in coastal marine environments}, volume={162}, ISSN={["1872-7581"]}, DOI={10.1016/j.marchem.2014.03.006}, abstractNote={Absorbance and fluorescence measurements were measured on base-extracted particulate organic matter (BEPOM) to examine POM biogeochemistry in coastal marine environments. BEPOM trends from August 2011–September 2012 in the Neuse River Estuary (NRE) were compared against single sampling events in Charleston Harbor (CHS) and the inner Louisiana–Texas Shelf of the Gulf of Mexico (GOM) in July 2011 and July 2012, respectively. Spectral slope values, S275–295, and the ratio of spectral slopes, SR values, were mainly influenced by distinct structure in the UV-B region of BEPOM absorption spectra, which was similar to prior laboratory work on autochthonous, planktonic sources of chromophoric dissolved organic matter (CDOM). A PARAFAC model with five components was fit to BEPOM excitation–emission matrix (EEM) fluorescence data. Excitation and emission spectra of the five components were similar to those found for dissolved organic matter (DOM) in other coastal environments, with two components attributed to planktonic sources and two components attributed to terrestrial (humic) sources. A fifth component was attributed to microbial humic substances. Principle components analysis of PARAFAC results separated autochthonous, planktonic components from allochthonous, terrestrial components and explained > 70% of the variance in the data. Surface water stable carbon isotope (δ13C) values of BEPOM from the NRE and CHS ranged from − 29 to − 23‰, with most enriched values occurring synchronous with high Chl-a concentrations, and indicating that enriched δ13C values in BEPOM reflected a planktonic source. Notably, δ13C-BEPOM values for the GOM shelf below 50 m water depth were depleted (<− 30‰), and a mixing model indicated that 30–40% of the POM could originate from methanic carbon. BEPOM absorption and fluorescence results suggested a planktonic POM as a source of CDOM in coastal marine environments.}, journal={MARINE CHEMISTRY}, publisher={Elsevier BV}, author={Brym, Adeline and Paerl, Hans W. and Montgomery, Michael T. and Handsel, Lauren T. and Ziervogel, Kai and Osburn, Christopher L.}, year={2014}, month={May}, pages={96–113} } @inbook{osburn_del vecchio_boyd_2014, title={Physicochemical Effects on Dissolved Organic Matter Fluorescence in Natural Waters}, ISBN={9781139045452}, url={http://dx.doi.org/10.1017/cbo9781139045452.012}, DOI={10.1017/cbo9781139045452.012}, booktitle={Aquatic Organic Matter Fluorescence}, publisher={Cambridge University Press}, author={Osburn, Christopher L. and Del Vecchio, Rossana and Boyd, Thomas J.}, editor={Coble, Paula and Lead, Jaimie and Baker, Andy and Reynolds, Darren M. and Spencer, Robert G.M.Editors}, year={2014}, month={Jun}, pages={233–277} } @article{osburn_del vecchio_boyd_2014, title={Physicochemical effects on dissolved organic matter fluorescence in natural waters}, journal={Aquatic organic matter fluorescence}, author={Osburn, C. L. and Del Vecchio, R. and Boyd, T. J.}, year={2014}, pages={233–277} } @article{guo_yang_zhai_chen_osburn_huang_li_2014, title={Runoff-mediated seasonal oscillation in the dynamics of dissolved organic matter in different branches of a large bifurcated estuary-The Changjiang Estuary}, volume={119}, ISSN={2169-8953}, url={http://dx.doi.org/10.1002/2013JG002540}, DOI={10.1002/2013jg002540}, abstractNote={AbstractThe Changjiang Estuary is a large bifurcated estuary where different hydrodynamic processes influence its South Branch compared to its North Branch. The South Branch is the dominant pathway of Changjiang River discharge, while the shallower and narrower North Branch is dominated by salt water intrusion, especially in the dry season. Absorption and fluorescence spectroscopy were measured along with dissolved organic carbon (DOC) concentrations to characterize the properties of dissolved organic matter (DOM) collected in different seasons during an extreme drought year in 2011. The refractory DOM from the Changjiang River flowed mainly through the South Branch, whereas in the lower South Branch, the input from the polluted Huangpu River contributed a large amount of biolabile DOM, demonstrating an anthropogenic perturbation from megacities. The DOM properties in the North Branch showed conservative behavior in the wet season, while noticeable addition was observed in the dry season, accompanied by the reversed flux of DOM from the North Branch to the South Branch, emphasizing the regular seasonal oscillation of the DOM dynamics in this monsoon‐controlled bifurcated estuary. The estuarine turbidity maximum zones played distinct roles on DOM dynamics in different estuarine environments. The DOC and chromophoric DOM (CDOM) abundance in the Changjiang River and other Chinese rivers were at lower levels compared to other world rivers, showing a characteristic of the regional CDOM‐poor features for many East Asia rivers.}, number={5}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Guo, Weidong and Yang, Liyang and Zhai, Weidong and Chen, Wenzhao and Osburn, Christopher L. and Huang, Xiao and Li, Yan}, year={2014}, month={May}, pages={776–793} } @article{dixon_osburn_paerl_peierls_2014, title={Seasonal changes in estuarine dissolved organic matter due to variable flushing time and wind-driven mixing events}, volume={151}, ISSN={["1096-0015"]}, DOI={10.1016/j.ecss.2014.10.013}, abstractNote={This study examined the seasonality of dissolved organic matter (DOM) sources and transformations within the Neuse River estuary (NRE) in eastern North Carolina between March 2010 and February 2011. During this time, monthly surface and bottom water samples were collected along the longitudinal axis of the NRE, ranging from freshwater to mesohaline segments. The monthly mean of all surface and bottom measurements made on collected samples was used to clarify larger physical mixing controls in the estuary as a whole. By comparing monthly mean trends in DOM and chromophoric dissolved organic matter (CDOM) properties in surface and bottom waters during varying hydrological conditions, we found that DOM and CDOM quality in the NRE is controlled by a combination of discharge, wind speed, and wind direction. The quality of DOM was assessed using C:N ratios, specific ultraviolet absorption at 254 nm (SUVA254), the absorption spectral slope ratio (SR), and the humification (HIX) and biological (BIX) indices from fluorescence. The NRE reflects allochthonous sources when discharge and flushing time are elevated at which times SUVA254 and HIX increased relative to base flow. During periods of reduced discharge and long flushing times in the estuary, extensive autochthonous production modifies the quality of the DOM pool in the NRE. This was evidenced by falling C:N values, and higher BIX and SR values. Lastly, a combination of increased wind speed and shifts in wind direction resulted in benthic resuspension events of degraded, planktonic OM. Thus, the mean DOM characteristics in this shallow micro-tidal estuary can be rapidly altered during episodic mixing events on timescales of a few weeks.}, journal={ESTUARINE COASTAL AND SHELF SCIENCE}, publisher={Elsevier BV}, author={Dixon, Jennifer L. and Osburn, Christopher L. and Paerl, Hans W. and Peierls, Benjamin L.}, year={2014}, month={Dec}, pages={210–220} } @book{montgomery_boyd_coffin_drake_hansen_osburn_2014, place={Washington DC}, title={TNT Degradation by Natural Microbial Assemblages at Frontal Boundaries Between Water Masses in Coastal Ecosystems (ER-2124 interim report)}, number={NRL/MR/6110--14-9552}, institution={Chemical Dynamics and Diagnostics Branch Naval Research Lab}, author={Montgomery, M.T. and Boyd, T.J. and Coffin, R.B. and Drake, L.A. and Hansen, L.T. and Osburn, C.L.}, year={2014} } @article{etheridge_birgand_osborne_osburn_burchell_irving_2014, title={Using in situ ultraviolet-visual spectroscopy to measure nitrogen, carbon, phosphorus, and suspended solids concentrations at a high frequency in a brackish tidal marsh}, volume={12}, ISSN={1541-5856}, url={http://dx.doi.org/10.4319/lom.2014.12.10}, DOI={10.4319/lom.2014.12.10}, abstractNote={The collection of high frequency water quality data are key to making the next leap in hydrological and biogeochemical sciences. Commercially available in situ ultraviolet‐visual (UV‐Vis) spectrometers make possible the long‐term collection of absorption spectra multiple times per hour. This technology has proven useful for measuring nitrate, dissolved organic carbon, and total suspended solids in many environments, but has not been tested in tidal marsh conditions where upstream freshwater mixes with estuarine waters, resulting in rapid changes in concentrations and salinity. These three parameters encompass only a portion of the nutrients that are of interest in these systems. To test the potential of spectroscopy to measure these and other nutrient concentrations, spectrometers were installed in a constructed brackish tidal marsh and absorbance spectra were compared to lab analyses for coinciding discrete samples. Variable selection techniques, including partial least squares regression, lasso regression, and stepwise regression, were used to develop models with which nitrate, total kjeldahl nitrogen, dissolved organic carbon, phosphate, total phosphorus, total suspended solids, and salinity in brackish marsh waters can be predicted from UV‐Vis spectrometer measurements. Significant relationships between the absorption spectra and the laboratory measured concentrations were observed for all of the parameters. Phosphate and total phosphorus were the only nutrients which had R2 values less than 0.86 for their best calibrations. This study shows the potential to collect multiple water quality parameters at a high frequency in brackish waters using in situ spectrometers and gives the tools to replicate this analysis in all environments.}, number={1}, journal={Limnology and Oceanography: Methods}, publisher={Wiley}, author={Etheridge, J. Randall and Birgand, François and Osborne, Jason A. and Osburn, Christopher L. and Burchell, Michael R., II and Irving, Justin}, year={2014}, month={Jan}, pages={10–22} } @article{genereux_nagy_osburn_oberbauer_2013, title={A connection to deep groundwater alters ecosystem carbon fluxes and budgets: Example from a Costa Rican rainforest}, volume={40}, ISSN={0094-8276}, url={http://dx.doi.org/10.1002/grl.50423}, DOI={10.1002/grl.50423}, abstractNote={AbstractField studies of watershed carbon fluxes and budgets are critical for understanding the carbon cycle, but the role of deep regional groundwater is poorly known and field examples are lacking. Here we show that discharge of regional groundwater into a lowland Costa Rican rainforest has a major influence on ecosystem carbon fluxes. This influence is observable through chemical, isotopic, and flux signals in groundwater, surface water, and air. Not addressing the influence of regional groundwater in the field measurement program and data analysis would give a misleading impression of the overall carbon source or sink status of the rainforest. In quantifying a carbon budget with the traditional “small watershed” mass balance approach, it would be critical at this site and likely many others to consider watershed inputs or losses associated with exchange between the ecosystem and the deeper hydrogeological system on which it sits.}, number={10}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Genereux, David P. and Nagy, Laura A. and Osburn, Christopher L. and Oberbauer, Steven F.}, year={2013}, month={May}, pages={2066–2070} } @article{tehrani_eurico j. d'sa_osburn_bianchi_schaeffer_2013, title={Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS) and MERIS Sensors: Case Study for the Northern Gulf of Mexico}, volume={5}, ISSN={["2072-4292"]}, DOI={10.3390/rs5031439}, abstractNote={Empirical band ratio algorithms for the estimation of colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) for Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS) and MERIS ocean color sensors were assessed and developed for the northern Gulf of Mexico. Match-ups between in situ measurements of CDOM absorption coefficients at 412 nm (aCDOM(412)) with that derived from SeaWiFS were examined using two previously reported reflectance band ratio algorithms. Results indicate better performance using the Rrs(510)/Rrs(555) (Bias = −0.045; RMSE = 0.23; SI = 0.49, and R2 = 0.66) than the Rrs(490)/Rrs(555) reflectance band ratio algorithm. Further, a comparison of aCDOM(412) retrievals using the Rrs(488)/Rrs(555) for MODIS and Rrs(510)/Rrs(560) for MERIS reflectance band ratios revealed better CDOM retrievals with MERIS data. Since DOC cannot be measured directly by remote sensors, CDOM as the colored component of DOC is utilized as a proxy to estimate DOC remotely. A seasonal relationship between CDOM and DOC was established for the summer and spring-winter with high correlation for both periods (R2~0.9). Seasonal band ratio empirical algorithms to estimate DOC were thus developed using the relationships between CDOM-Rrs and seasonal CDOM-DOC for SeaWiFS, MODIS and MERIS. Results of match-up comparisons revealed DOC estimates by both MODIS and MERIS to be relatively more accurate during summer time, while both of them underestimated DOC during spring-winter time. A better DOC estimate from MERIS in comparison to MODIS in spring-winter could be attributed to its similarity with the SeaWiFS band ratio CDOM algorithm.}, number={3}, journal={REMOTE SENSING}, publisher={MDPI AG}, author={Tehrani, Nazanin Chaichi and Eurico J. D'Sa and Osburn, Christopher L. and Bianchi, Thomas S. and Schaeffer, Blake A.}, year={2013}, month={Mar}, pages={1439–1464} } @article{chaichitehrani_d'sa_ko_walker_osburn_chen_2014, title={Colored Dissolved Organic Matter Dynamics in the Northern Gulf of Mexico from Ocean Color and Numerical Model Results}, volume={296}, ISSN={0749-0208 1551-5036}, url={http://dx.doi.org/10.2112/JCOASTRES-D-13-00036.1}, DOI={10.2112/jcoastres-d-13-00036.1}, abstractNote={ABSTRACT Chaichitehrani, N.; D'Sa, E.J.; Ko, D.S.; Walker, N.D.; Osburn, C.L., and Chen, R.F., 2014. Colored dissolved organic matter dynamics in the Northern Gulf of Mexico from ocean color and numerical model results. Colored dissolved organic matter (CDOM) absorption and salinity relationships were assessed and used in conjunction with the salinity and current outputs of a numerical model (Navy Coastal Ocean Model [NCOM]) to study CDOM dynamics in the northern Gulf of Mexico. In situ CDOM absorption and salinity obtained from multiple field campaigns were inversely correlated seasonally (winter–spring and summer) and latitudinally (inner- and outer-shelf zones), suggesting conservative behavior of CDOM distribution. A weaker correlation, during summer in the outer-shelf zone, however, indicated stronger effects of photooxidation and lower masking effects from riverine CDOM. Applying these relationships to simulated salinity resulted in hourly maps of CDOM that revealed similarities to CDOM patterns derived from SeaWiFS satellite imagery. Further, matchup comparisons between model-derived and in situ CDOM absorption were statistically sound for the summer (bias = −0.016, root mean square error = 0.059, r2 = 0.51 SI = 0.28) and the winter–spring periods (bias = 0.033, root mean square error = 0.099, r2 = 0.52, SI = 0.21). Overlaying the model-derived CDOM maps on the simulated currents revealed the strong influence of currents on CDOM advection. Downcoast currents during the nonsummer months led to persistent advection of CDOM westward interrupted by frequent cold front events that flush CDOM-laden waters out of the coastal bays onto the inner and outer continental shelves. In contrast, the upcoast current regime, though less well organized, produces a more significant seaward advection of CDOM, likely due to the Ekman transport and subsequent entrainment by mesoscale eddies over the continental slope.}, number={4}, journal={Journal of Coastal Research}, publisher={Coastal Education and Research Foundation}, author={Chaichitehrani, Nazanin and D'Sa, Eurico J. and Ko, Dong S. and Walker, Nan D. and Osburn, Christopher L. and Chen, Robert F.}, year={2014}, month={Jul}, pages={800–814} } @article{voli_wegmann_bohnenstiehl_leithold_osburn_polyakov_2013, title={Fingerprinting the sources of suspended sediment delivery to a large municipal drinking water reservoir: Falls Lake, Neuse River, North Carolina, USA}, volume={13}, ISSN={["1614-7480"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84887284036&partnerID=MN8TOARS}, DOI={10.1007/s11368-013-0758-3}, number={10}, journal={JOURNAL OF SOILS AND SEDIMENTS}, publisher={Springer Science \mathplus Business Media}, author={Voli, Mark T. and Wegmann, Karl W. and Bohnenstiehl, DelWayne R. and Leithold, Elana and Osburn, Christopher L. and Polyakov, Viktor}, year={2013}, month={Dec}, pages={1692–1707} } @article{osburn_stedmon_spencer_stubbins_2013, title={LINKING OPTICAL AND CHEMICAL PROPERTIES OF DISSOLVED ORGANIC MATTER IN NATURAL WATERS}, volume={22}, ISSN={1539-607X}, url={http://dx.doi.org/10.1002/lob.201322378}, DOI={10.1002/lob.201322378}, abstractNote={First, we came to understand that it was not only our role, but our responsibility, as scientists to advocate for science in the public domain. Scientists simply cannot afford to sit on the sidelines as governments defund and dismantle vital scientific programs, such as the ELA. In spite of this, science advocacy is not typically encouraged by universities and other research institutions. Perhaps, it is time to change the culture that disuades scientists from engaging in science advocacy. Second, we discovered some necessary tools were missing from our toolkit. For example, we had to research the democratic options available to citizens to lobby government, as well as learn the procedures for distributing press releases and media advisories to journalists. We also needed to become proficient in using various types of social media to broadcast information. In hindsight, this capacity should have been in place for the ELA years ago in the form of an active outreach organization. Third, we quickly appreciated that effective communication is key to getting a message to resonate with the public. This involves learning not only how to distill complex scientific concepts to their essence in an interesting manner, but also how to explain the importance of science within the context of societal values. For most scientists, speaking in sound bites is not a natural talent, but an acquired skill – and one that should be taught and practised. Fourth, we realized that our professional connections within the scientific community were not, by themselves, adequate for this work. We needed to forge new relationships with politicians, journalists, industry leaders, unions, First Nations, environmental organizations, among others. The lesson here is for scientists to effectively interact with the public to build a broad and diverse network of supporters, as this enables allies to be efficiently mobilized when crises arise. Finally, we learned to take ownership of past mistakes. If we had done a better job of engaging the public in our science in the first place, perhaps it may have prevented the government from cutting funding for the ELA. Public outreach over the last four decades should have showcased the applied and relevant research being done at the ELA on the public’s behalf. If we are doing science ‘in the public good,’ the public has to know about it – and it is our job, as scientists, to be the voice for science.}, number={3}, journal={Limnology and Oceanography Bulletin}, publisher={Wiley}, author={Osburn, Christopher L. and Stedmon, Colin A. and Spencer, Robert G. M. and Stubbins, Aron}, year={2013}, month={Aug}, pages={78–82} } @article{zhang_liu_osburn_wang_qin_zhou_2013, title={Photobleaching Response of Different Sources of Chromophoric Dissolved Organic Matter Exposed to Natural Solar Radiation Using Absorption and Excitation-Emission Matrix Spectra}, volume={8}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0077515}, abstractNote={CDOM biogeochemical cycle is driven by several physical and biological processes such as river input, biogeneration and photobleaching that act as primary sinks and sources of CDOM. Watershed-derived allochthonous (WDA) and phytoplankton-derived autochthonous (PDA) CDOM were exposed to 9 days of natural solar radiation to assess the photobleaching response of different CDOM sources, using absorption and fluorescence (excitation-emission matrix) spectroscopy. Our results showed a marked decrease in total dissolved nitrogen (TDN) concentration under natural sunlight exposure for both WDA and PDA CDOM, indicating photoproduction of ammonium from TDN. In contrast, photobleaching caused a marked increase in total dissolved phosphorus (TDP) concentration for both WDA and PDA CDOM. Thus TDN∶TDP ratios decreased significantly both for WDA and PDA CDOM, which partially explained the seasonal dynamic of TDN∶TDP ratio in Lake Taihu. Photobleaching rate of CDOM absorption a(254), was 0.032 m/MJ for WDA CDOM and 0.051 m/MJ for PDA CDOM from days 0–9, indicating that phototransformations were initially more rapid for the newly produced CDOM from phytoplankton than for the river CDOM. Extrapolation of these values to the field indicated that 3.9%–5.1% CDOM at the water surface was photobleached and mineralized every day in summer in Lake Taihu. Photobleaching caused the increase of spectral slope, spectral slope ratio and molecular size, indicating the CDOM mean molecular weight decrease which was favorable to further microbial degradation of mineralization. Three fluorescent components were validated in parallel factor analysis models calculated separately for WDA and PDA CDOM. Our study suggests that the humic-like fluorescence materials could be rapidly and easily photobleached for WDA and PDA CDOM, but the protein-like fluorescence materials was not photobleached and even increased from the transformation of the humic-like fluorescence substance to the protein-like fluorescence substance. Photobleaching was an important driver of CDOM and nutrients biogeochemistry in lake water.}, number={10}, journal={PLOS ONE}, publisher={Public Library of Science (PLoS)}, author={Zhang, Yunlin and Liu, Xiaohan and Osburn, Christopher L. and Wang, Mingzhu and Qin, Boqiang and Zhou, Yongqiang}, editor={Chin, Wei-ChunEditor}, year={2013}, month={Oct} } @article{levas_grottoli_hughes_osburn_matsui_2013, title={Physiological and Biogeochemical Traits of Bleaching and Recovery in the Mounding Species of Coral Porites lobata: Implications for Resilience in Mounding Corals}, volume={8}, DOI={10.1371/journal.pone.0063267}, abstractNote={Mounding corals survive bleaching events in greater numbers than branching corals. However, no study to date has determined the underlying physiological and biogeochemical trait(s) that are responsible for mounding coral holobiont resilience to bleaching. Furthermore, the potential of dissolved organic carbon (DOC) as a source of fixed carbon to bleached corals has never been determined. Here, Porites lobata corals were experimentally bleached for 23 days and then allowed to recover for 0, 1, 5, and 11 months. At each recovery interval a suite of analyses were performed to assess their recovery (photosynthesis, respiration, chlorophyll a, energy reserves, tissue biomass, calcification, δ13C of the skeletal, δ13C, and δ15N of the animal host and endosymbiont fractions). Furthermore, at 0 months of recovery, the assimilation of photosynthetically acquired and zooplankton-feeding acquired carbon into the animal host, endosymbiont, skeleton, and coral-mediated DOC were measured via 13C-pulse-chase labeling. During the first month of recovery, energy reserves and tissue biomass in bleached corals were maintained despite reductions in chlorophyll a, photosynthesis, and the assimilation of photosynthetically fixed carbon. At the same time, P. lobata corals catabolized carbon acquired from zooplankton and seemed to take up DOC as a source of fixed carbon. All variables that were negatively affected by bleaching recovered within 5 to 11 months. Thus, bleaching resilience in the mounding coral P. lobata is driven by its ability to actively catabolize zooplankton-acquired carbon and seemingly utilize DOC as a significant fixed carbon source, facilitating the maintenance of energy reserves and tissue biomass. With the frequency and intensity of bleaching events expected to increase over the next century, coral diversity on future reefs may favor not only mounding morphologies but species like P. lobata, which have the ability to utilize heterotrophic sources of fixed carbon that minimize the impact of bleaching and promote fast recovery.}, number={5}, journal={PLoS ONE}, publisher={Public Library of Science (PLoS)}, author={Levas, Stephen J. and Grottoli, Andréa G. and Hughes, Adam and Osburn, Christopher L. and Matsui, Yohei}, editor={Harder, TilmannEditor}, year={2013}, month={May}, pages={e63267} } @article{meskhidze_petters_tsigaridis_bates_o'dowd_reid_lewis_gantt_anguelova_bhave_et al._2013, title={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, volume={14}, ISSN={1530-261X}, url={http://dx.doi.org/10.1002/asl2.441}, DOI={10.1002/asl2.441}, abstractNote={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, number={4}, journal={Atmospheric Science Letters}, publisher={Wiley}, author={Meskhidze, Nicholas and Petters, Markus D. and Tsigaridis, Kostas and Bates, Tim and O'Dowd, Colin and Reid, Jeff and Lewis, Ernie R. and Gantt, Brett and Anguelova, Magdalena D. and Bhave, Prakash V. and et al.}, year={2013}, month={Jun}, pages={207–213} } @article{meskhidze_petters_tsigaridis_bates_o'dowd_reid_lewis_gantt_anguelova_bhave_et al._2013, title={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, volume={14}, number={4}, journal={Atmospheric Science Letters}, author={Meskhidze, N. and Petters, M. D. and Tsigaridis, K. and Bates, T. and O'Dowd, C. and Reid, J. and Lewis, E. R. and Gantt, B. and Anguelova, M. D. and Bhave, P. V. and et al.}, year={2013}, pages={207–213} } @article{zhou_guo_shiller_lohrenz_asper_osburn_2013, title={Characterization of oil components from the Deepwater Horizon oil spill in the Gulf of Mexico using fluorescence EEM and PARAFAC techniques}, volume={148}, ISSN={["1872-7581"]}, DOI={10.1016/j.marchem.2012.10.003}, abstractNote={Three-dimensional (3D) fluorescence spectroscopy and parallel factor analysis (PARAFAC) were used to characterize oil components and to examine their fate and transformation processes during the unprecedented Deepwater Horizon oil spill in the Gulf of Mexico. Water samples were collected during two cruises in May and June 2010 soon after the spill began. Fluorescence excitation-emission matrix (EEM) spectra of seawater samples strongly resemble those of crude oil from the Macondo well and weathered oil collected from Gulf surface waters. This indicates the influence of oil on marine dissolved organic matter (DOM) which yielded elevated dissolved organic carbon (DOC) concentrations, higher UV–vis absorbance, and higher optically inferred molecular weight DOM in the water column. Two major types of DOM were found in the water column: one with low abundance but high optical activity and the other with high mass concentration yet low optical activity. Higher specific UV absorbance but lower spectral slope values observed for deep-water samples indicates the presence of less degraded or fresher crude oil in deep waters. Results of PARAFAC modeling revealed three oil-related components corresponding to crude and weathered oil in the water column: the most prominent one (namely C1) centered on Ex/Em 226/340 nm and the other two components (C2 and C6) centered on 236/360 and 252/311 nm, respectively. In addition, there is another DOM component (C3), partially representing chemically dispersed oil. Interestingly, the oil component ratios, an intensive property, varied with time and the degradation status of oil. We hypothesize that C2 (236/360 nm) is mostly a degraded product while C6 (252/311 nm) is a crude oil component with lower molecular weight, but at the same time, could be derived from oil degradation. Changes in fluorescence component ratios can thus be used as a compelling index to track the fate and transport of oil in marine environments.}, journal={MARINE CHEMISTRY}, publisher={Elsevier BV}, author={Zhou, Zhengzhen and Guo, Laodong and Shiller, Alan M. and Lohrenz, Steven E. and Asper, Vernon L. and Osburn, Christopher L.}, year={2013}, month={Jan}, pages={10–21} } @article{bianchi_garcia-tigreros_yvon-lewis_shields_mills_butman_osburn_raymond_shank_dimarco_et al._2013, title={Enhanced transfer of terrestrially derived carbon to the atmosphere in a flooding event}, volume={40}, ISSN={0094-8276}, url={http://dx.doi.org/10.1029/2012GL054145}, DOI={10.1029/2012gl054145}, abstractNote={AbstractRising CO2 concentration in the atmosphere, global climate change, and the sustainability of the Earth's biosphere are great societal concerns for the 21st century. Global climate change has, in part, resulted in a higher frequency of flooding events, which allow for greater exchange between soil/plant litter and aquatic carbon pools. Here we demonstrate that the summer 2011 flood in the Mississippi River basin, caused by extreme precipitation events, resulted in a “flushing” of terrestrially derived dissolved organic carbon (TDOC) to the northern Gulf of Mexico. Data from the lower Atchafalaya and Mississippi rivers showed that the DOC flux to the northern Gulf of Mexico during this flood was significantly higher than in previous years. We also show that consumption of radiocarbon‐modern TDOC by bacteria in floodwaters in the lower Atchafalaya River and along the adjacent shelf contributed to northern Gulf shelf waters changing from a net sink to a net source of CO2 to the atmosphere in June and August 2011. This work shows that enhanced flooding, which may or may not be caused by climate change, can result in rapid losses of stored carbon in soils to the atmosphere via processes in aquatic ecosystems.}, number={1}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Bianchi, Thomas S. and Garcia-Tigreros, Fenix and Yvon-Lewis, Shari A. and Shields, Michael and Mills, Heath J. and Butman, David and Osburn, Christopher and Raymond, Peter and Shank, G. Christopher and DiMarco, Steven F. and et al.}, year={2013}, month={Jan}, pages={116–122} } @article{osburn_handsel_mikan_paerl_montgomery_2012, title={Fluorescence Tracking of Dissolved and Particulate Organic Matter Quality in a River-Dominated Estuary}, volume={46}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/es3007723}, DOI={10.1021/es3007723}, abstractNote={Excitation-emission matrix (EEM) fluorescence was combined with parallel factor analysis (PARAFAC) to model base-extracted particulate (POM) and dissolved (DOM) organic matter quality in the Neuse River Estuary (NRE), North Carolina, before and after passage of Hurricane Irene in August 2011. Principle components analysis was used to determine that four of the PARAFAC components (C1-C3 and C6) were terrestrial sources to the NRE. One component (C4), prevalent in DOM of nutrient-impacted streams and estuaries and produced in phytoplankton cultures, was enriched in the POM and in surface sediment pore water DOM. One component (C5) was related to recent autochthonous production. Photoexposure of unfiltered Neuse River water caused an increase in slope ratio values (S(R)) which corresponded to an increase in the ratio C2:C3 for DOM, and the production of C4 fluorescence in both POM and DOM. Changes to the relative abundance of C4 in POM and DOM indicated that advection of pore water DOM from surface sediments into overlying waters could increase the autochthonous quality of DOM in shallow microtidal estuaries. Modeling POM and DOM simultaneously with PARAFAC is an informative technique that is applicable to assessments of estuarine water quality.}, number={16}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Osburn, Christopher L. and Handsel, Lauren T. and Mikan, Molly P. and Paerl, Hans W. and Montgomery, Michael T.}, year={2012}, month={Jul}, pages={8628–8636} } @article{montgomery_coffin_boyd_osburn_2013, title={Incorporation and mineralization of TNT and other anthropogenic organics by natural microbial assemblages from a small, tropical estuary}, volume={174}, ISSN={0269-7491}, url={http://dx.doi.org/10.1016/j.envpol.2012.11.036}, DOI={10.1016/j.envpol.2012.11.036}, abstractNote={2,4,6-Trinitrotoluene (TNT) metabolism was compared across salinity transects in Kahana Bay, a small tropical estuary on Oahu, HI. In surface water, TNT incorporation rates (range: 3-121 μg C L(-1) d(-1)) were often 1-2 orders of magnitude higher than mineralization rates suggesting that it may serve as organic nitrogen for coastal microbial assemblages. These rates were often an order of magnitude more rapid than those for RDX and two orders more than HMX. During average or high stream flow, TNT incorporation was most rapid at the riverine end member and generally decreased with increasing salinity. This pattern was not seen during low flow periods. Although TNT metabolism was not correlated with heterotrophic growth rate, it may be related to metabolism of other aromatic compounds. With most TNT ring-carbon incorporation efficiencies at greater than 97%, production of new biomass appears to be a more significant product of microbial TNT metabolism than mineralization.}, journal={Environmental Pollution}, publisher={Elsevier BV}, author={Montgomery, Michael T. and Coffin, Richard B. and Boyd, Thomas J. and Osburn, Christopher L.}, year={2013}, month={Mar}, pages={257–264} } @article{ziervogel_mckay_rhodes_osburn_dickson-brown_arnosti_teske_2012, title={Microbial Activities and Dissolved Organic Matter Dynamics in Oil-Contaminated Surface Seawater from the Deepwater Horizon Oil Spill Site}, volume={7}, ISSN={1932-6203}, url={http://dx.doi.org/10.1371/journal.pone.0034816}, DOI={10.1371/journal.pone.0034816}, abstractNote={The Deepwater Horizon oil spill triggered a complex cascade of microbial responses that reshaped the dynamics of heterotrophic carbon degradation and the turnover of dissolved organic carbon (DOC) in oil contaminated waters. Our results from 21-day laboratory incubations in rotating glass bottles (roller bottles) demonstrate that microbial dynamics and carbon flux in oil-contaminated surface water sampled near the spill site two weeks after the onset of the blowout were greatly affected by activities of microbes associated with macroscopic oil aggregates. Roller bottles with oil-amended water showed rapid formation of oil aggregates that were similar in size and appearance compared to oil aggregates observed in surface waters near the spill site. Oil aggregates that formed in roller bottles were densely colonized by heterotrophic bacteria, exhibiting high rates of enzymatic activity (lipase hydrolysis) indicative of oil degradation. Ambient waters surrounding aggregates also showed enhanced microbial activities not directly associated with primary oil-degradation (β-glucosidase; peptidase), as well as a twofold increase in DOC. Concurrent changes in fluorescence properties of colored dissolved organic matter (CDOM) suggest an increase in oil-derived, aromatic hydrocarbons in the DOC pool. Thus our data indicate that oil aggregates mediate, by two distinct mechanisms, the transfer of hydrocarbons to the deep sea: a microbially-derived flux of oil-derived DOC from sinking oil aggregates into the ambient water column, and rapid sedimentation of the oil aggregates themselves, serving as vehicles for oily particulate matter as well as oil aggregate-associated microbial communities.}, number={4}, journal={PLoS ONE}, publisher={Public Library of Science (PLoS)}, author={Ziervogel, Kai and McKay, Luke and Rhodes, Benjamin and Osburn, Christopher L. and Dickson-Brown, Jennifer and Arnosti, Carol and Teske, Andreas}, editor={Chin, Wei-ChunEditor}, year={2012}, month={Apr}, pages={e34816} } @book{montgomery_coffin_boyd_osburn_2012, place={Washington DC}, title={TNT biodegradation by natural microbial assemblages at estuarine frontal boundaries}, number={NRL/MR/6110--12-9390}, institution={Chemical Dynamics and Diagnostics Branch Naval Research Lab}, author={Montgomery, M.T. and Coffin, R.B. and Boyd, T.J. and Osburn, C.L.}, year={2012} } @article{montgomery_boyd_smith_walker_osburn_2011, title={2,4,6-Trinitrotoluene Mineralization and Incorporation by Natural Bacterial Assemblages in Coastal Ecosystems}, DOI={10.1021/bk-2011-1069.ch009}, abstractNote={Because of logistical and technical challenges to studying energetics in coastal environments, lab and terrestrial data are often extrapolated to aquatic field sites. We found measurable TNT mineralization rates from natural microbial assemblages in several coastal ecosystems unlikely to have a history of exposure to energetics. During nine sampling events in coastal waterways from 2002 to 2010, we measured TNT mineralization rates in surface sediment and water samples that were often the same order of magnitude as the rate of total heterotrophic bacterial metabolism. These rates were often similar to those of other organic compounds that are transient in natural ecosystems such as petroleum hydrocarbons and amino acids - due to their use in bacterial metabolism.}, journal={Environmental Chemistry of Explosives and Propellant Compounds in Soils and Marine Systems: Distributed Source Characterization and Remedial Technologies}, publisher={American Chemical Society (ACS)}, author={Montgomery, Michael T. and Boyd, Thomas J. and Smith, Joseph P. and Walker, Shelby E. and Osburn, Christopher L.}, year={2011}, month={Jan}, pages={171–184} } @article{montgomery_coffin_boyd_smith_walker_osburn_2011, title={2,4,6-Trinitrotoluene mineralization and bacterial production rates of natural microbial assemblages from coastal sediments}, volume={159}, ISSN={0269-7491}, url={http://dx.doi.org/10.1016/j.envpol.2011.07.018}, DOI={10.1016/j.envpol.2011.07.018}, abstractNote={The nitrogenous energetic constituent, 2,4,6-Trinitrotoluene (TNT), is widely reported to be resistant to bacterial mineralization (conversion to CO2); however, these studies primarily involve bacterial isolates from freshwater where bacterial production is typically limited by phosphorus. This study involved six surveys of coastal waters adjacent to three biome types: temperate broadleaf, northern coniferous, and tropical. Capacity to catabolize and mineralize TNT ring carbon to CO2 was a common feature of natural sediment assemblages from these coastal environments (ranging to 270+/−38 μg C kg−1 d−1). More importantly, these mineralization rates comprised a significant proportion of total heterotrophic production. The finding that most natural assemblages surveyed from these ecosystems can mineralize TNT ring carbon to CO2 is consistent with recent reports that assemblage components can incorporate TNT ring carbon into bacterial biomass. These data counter the widely held contention that TNT is recalcitrant to bacterial catabolism of the ring carbon in natural environments.}, number={12}, journal={Environmental Pollution}, publisher={Elsevier BV}, author={Montgomery, Michael T. and Coffin, Richard B. and Boyd, Thomas J. and Smith, Joseph P. and Walker, Shelby E. and Osburn, Christopher L.}, year={2011}, month={Dec}, pages={3673–3680} } @article{osburn_wigdahl_fritz_saros_2011, title={Dissolved organic matter composition and photoreactivity in prairie lakes of the U.S. Great Plains}, volume={56}, ISSN={0024-3590}, url={http://dx.doi.org/10.4319/lo.2011.56.6.2371}, DOI={10.4319/lo.2011.56.6.2371}, abstractNote={Dissolved organic matter (DOM) of 27 prairie saline lake ecosystems was investigated in the Northern and Central Great Plains of the United States using absorbance, fluorescence, lignin concentration, and stable C isotope values. The majority of variation in DOM fluorescence among lakes was due to humic (peak C) and microbially formed (peak M) fluorescent components, which appear to be derived from autochthonous primary production. Strong correlations between peak M and nutrients allow us to model total phosphorus (TP) concentration using peak M fluorescence and chromophoric dissolved organic matter (CDOM) absorption. The rate of primary production (PP) was positively correlated with peak M fluorescence and negatively with lignin concentration. Lignin phenol yields in the DOM were generally smaller than those of most freshwater systems. δ13C values of dissolved organic carbon (DOC) ranged from −25.0‰ to −20.1‰ and were generally enriched relative to typical freshwaters (ca. −27‰). Terrestrial DOM is degraded in prairie lakes, spanning a gradient from mixotrophic to eutrophic, as determined by a color–nutrient model. The photodegradation of autochthonous DOM was significant: CO2 fluxes from these prairie lakes, modeled from peak M fluorescence, ranged from 5 to 228 mmol C m−2 d−1 (median, 37 mmol C m−2 d−1) and was similar to community respiration estimated from protein fluorescence (median, 50 mmol C m−2 d−1). The combined estimates were about 50% of the global mean total C release previously reported for saline lake ecosystems. The implication of these new results is that the global C release from saline lake ecosystems is likely underestimated.}, number={6}, journal={Limnology and Oceanography}, publisher={Wiley}, author={Osburn, Christopher L. and Wigdahl, Courtney R. and Fritz, Sherilyn C. and Saros, Jasmine E.}, year={2011}, month={Nov}, pages={2371–2390} } @article{osburn_stedmon_2011, title={Linking the chemical and optical properties of dissolved organic matter in the Baltic–North Sea transition zone to differentiate three allochthonous inputs}, volume={126}, ISSN={0304-4203}, url={http://dx.doi.org/10.1016/j.marchem.2011.06.007}, DOI={10.1016/j.marchem.2011.06.007}, abstractNote={Optical and chemical properties of dissolved organic matter (DOM) were resolved in the mixing zone between the North Sea and the Baltic Sea. The results from four cruises undertaken from August 2006 to February 2007 are presented. Relationships between the optical (absorption and excitation–emission matrix (EEM) fluorescence), dissolved organic carbon (DOC), and dissolved lignin concentrations were determined and carbon stable isotope values (δ13C) of DOM were also used to evaluate DOM sources. Chromophoric DOM (CDOM), measured as absorption at 300 nm, was a strong predictor for DOC and lignin concentrations. The DOM fluorescence (FDOM) characteristics were modeled by parallel factor analysis (PARAFAC) and a six component model was derived. The intensity of one terrestrial humic-like fluorescent component (Fmax3) was strongly correlated to dissolved lignin concentrations. DOC concentrations were best modeled by the combination of this component with an amino acid-like fluorescent component. A three end-member mixing model developed for the region using CDOM–salinity relationships was used to estimate end-member lignin and DOC concentrations, which produced results consistent with other published results from the region. The Baltic Sea outflow was determined to be the dominant source of dissolved lignin in these waters. Despite the high riverine influence in the Jutland Coastal Current, the DOM originating from these waters contained little lignin and was predominantly autochthonous. Additionally CDOM and carbon stable isotope measurements revealed substantial autochthonous production in the Kattegat. Finally, we used the fluorescence–DOC relationships to estimate the net export of terrestrial C from the Baltic Sea at 0.8 Tg year− 1, which represents 45% of the calculated net DOC flux (1.7 Tg year− 1).}, number={1-4}, journal={Marine Chemistry}, publisher={Elsevier BV}, author={Osburn, Christopher L. and Stedmon, Colin A.}, year={2011}, month={Sep}, pages={281–294} } @article{tank_lesack_gareis_osburn_hesslein_2011, title={Multiple tracers demonstrate distinct sources of dissolved organic matter to lakes of the Mackenzie Delta, western Canadian Arctic}, volume={56}, DOI={10.4319/lo.2011.56.4.1297}, abstractNote={Lakes of the Mackenzie Delta occur across a gradient that contains three clear end members: those that remain connected to river‐water channels throughout the summer; those that receive only brief inputs of river water during an annual spring flood but contain dense macrophyte stands; and those that experience significant permafrost thaw along their margins. We measured dissolved organic carbon (DOC) concentration, dissolved organic matter (DOM) absorption and fluorescence, and stable isotopes of DOM, DOM precursor materials, and bacteria to elucidate the importance of river water, macrophytes, and thermokarst as DOM sources to Mackenzie Delta lakes. Despite standing stocks of macrophyte C that are sevenfold to 12‐fold greater than those of total DOC, stable isotopes indicated that autochthonous sources contributed less than 15% to overall DOM in macrophyte‐rich lakes. Instead, fluorescence and absorption indicated that the moderate summertime increase in DOC concentration in macrophyte‐rich lakes was the result of infrequent flushing, while bacterial δ13C indicated rapid bacterial removal of autochthonous DOC from the water column. In thermokarst lakes, summertime increases in DOC concentration were substantial, and stable isotopes indicated that much of this increase came from C released as a result of thermokarst‐related processes. Our results indicate that these distinct sources of DOM to neighboring arctic Delta lakes may drive between‐lake differences in C cycling and energy flow. Rapidly assimilated macrophyte DOM should be an important contributor to microbial food webs in our study lakes. In contrast, the accumulation of thermokarst‐origin DOM allows for a significant role in physico‐chemistry but indicates a lesser contribution of this DOM to higher trophic levels.}, number={4}, journal={Limnol. Oceanogr.}, publisher={Wiley-Blackwell}, author={Tank, Suzanne E. and Lesack, Lance F. W. and Gareis, Jolie A. L. and Osburn, Christopher L. and Hesslein, Ray H.}, year={2011}, month={May}, pages={1297–1309} } @article{pohlman_bauer_waite_osburn_chapman_2011, title={Methane hydrate-bearing seeps as a source of aged dissolved organic carbon to the oceans}, volume={4}, ISSN={["1752-0894"]}, DOI={10.1038/ngeo1016}, number={1}, journal={NATURE GEOSCIENCE}, publisher={Nature Publishing Group}, author={Pohlman, John W. and Bauer, James E. and Waite, William F. and Osburn, Christopher L. and Chapman, N. Ross}, year={2011}, month={Jan}, pages={37–41} } @article{stedmon_osburn_kragh_2010, title={Tracing water mass mixing in the Baltic–North Sea transition zone using the optical properties of coloured dissolved organic matter}, volume={87}, DOI={10.1016/j.ecss.2009.12.022}, abstractNote={The distribution and characteristics of coloured dissolved organic matter (CDOM) in the Baltic – North Sea transition zone were studied. The aim was to assess the validity of predicting CDOM absorption in the region on the basis of water mass mixing alone and demonstrate the utility of CDOM as an indicator of water mass mixing in coastal seas. A three-end-member mixing model representing the three major allochthonous CDOM sources was sufficient to describe the patterns in CDOM absorption distribution observed. The three-end-member water masses were the: Baltic outflow, German Bight and the central North Sea. Previously, it was thought that water from the German Bight transported northwards in the Jutland coastal current only sporadically influenced mixing between the Baltic and North Sea. The results from this study show that water from the German Bight is detectable at salinities down to 12 in the Kattegat and Belt Sea. On average, 23% of the CDOM in bottom waters of the Kattegat, Great Belt, Belt Sea, Arkona Sea and the Sound originated from the German Bight. Using this conservative mixing model approach, local CDOM inputs were detectable but found to be limited, representing only 0.25% of CDOM in the surface waters of the Kattegat and Belt Sea. The conservative mixing of CDOM makes it possible to predict its distribution and characteristics and offers a powerful tool for tracing water mass mixing in the region. The results also emphasize the need to include the Jutland Coastal current in hydrodynamic models for the region.}, number={1}, journal={Estuarine, Coastal and Shelf Science}, publisher={Elsevier BV}, author={Stedmon, Colin A. and Osburn, Christopher L. and Kragh, Theis}, year={2010}, month={Mar}, pages={156–162} } @article{boyd_barham_hall_osburn_2010, title={Variation in ultrafiltered and LMW organic matter fluorescence properties under simulated estuarine mixing transects: 1. Mixing alone}, volume={115}, ISSN={["2169-8961"]}, DOI={10.1029/2009jg000992}, abstractNote={Ultrafiltered and low molecular weight dissolved organic matter (UDOM and LMW‐DOM, respectively) fluorescence was studied under simulated estuarine mixing using samples collected from Delaware, Chesapeake, and San Francisco Bays (USA) transects. UDOM was concentrated by tangential flow ultrafiltration (TFF) from the marine (>33 PSU), mid‐estuarine (∼16 PSU), and freshwater (<1 PSU) members. TFF permeates (<1 kDa) from the three members were used to create artificial salinity transects ranging from ∼0 to ∼36, with 4 PSU increments. UDOM from the end‐ or mid‐members was added in equal amounts to each salinity‐mix. Three‐dimensional fluorescence excitation‐emission matrix (EEMs) spectra were generated for each end‐member permeate and UDOM through the full estuarine mixing transect. Fluorescence components such as proteinaceous, terrigenous, and marine derived humic peaks, and certain fluorescent ratios were noticeably altered by simulated estuarine mixing, suggesting that LMW DOM and UDOM undergo physicochemical alteration as they move to or from the freshwater, mid‐estuarine, or coastal ocean members. LMW fluorescence components fit a decreasing linear mixing model from mid salinities to the ocean end‐member, but were more highly fluorescent than mixing alone would predict in lower salinities (<8). Significant shifts were also seen in UDOM peak emission wavelengths with blue‐shifting toward the ocean end‐member. Humic‐type components in UDOM generally showed lower fluorescent intensities at low salinities, higher at mid‐salinities, and lower again toward the ocean end‐member. T (believed to be proteinaceous) and N (labile organic matter) peaks behaved similarly to each other, but not to B peak fluorescence, which showed virtually no variation in permeate or UDOM mixes with salinity. PCA and PARAFAC models showed similar results suggesting trends could be modeled for DOM end‐ and mid‐member sources. Changes in fluorescence properties due to estuarine mixing may be important when using CDOM as a proxy for DOM cycling in coastal systems.}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, publisher={Wiley-Blackwell}, author={Boyd, Thomas J. and Barham, Bethany P. and Hall, Gregory J. and Osburn, Christopher L.}, year={2010}, month={Sep} } @article{boyd_barham_hall_schumann_paerl_osburn_2010, title={Variation in ultrafiltered and LMW organic matter fluorescence properties under simulated estuarine mixing transects: 2. Mixing with photoexposure}, volume={115}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2009JG000994}, DOI={10.1029/2009jg000994}, abstractNote={Ultrafiltered and low molecular weight dissolved organic matter (UDOM and LMW‐DOM, respectively) fluorescence was studied under simulated estuarine mixing along with moderate photoexposure using Delaware, Chesapeake, and San Francisco Bays (USA) natural organic matter. UDOM was produced by tangential flow ultrafiltration (TFF) from the marine (>33 PSU), mid‐estuarine (∼16 PSU), and freshwater (<1 PSU) members. TFF permeates (<1 kDa) were used to create artificial salinity transects nominally ranging from ∼0 to ∼36, with 4 PSU increments. UDOM or permeate (as control) from freshwater and mid‐estuary was added to each salinity mix in the artificial transect to determine the impact of mixing behavior on optical properties. Three‐dimensional fluorescence excitation‐emission matrix (EEMs) spectra were generated for each end‐member permeate (LMW fraction) and UDOM through the full artificial mixing transect. Fluorescent properties representing standard‐identified peaks, fluorescence ratios and excitation‐emission characteristics were assayed as previously reported. However, in this study, each sample was additionally photobleached for three days (nominally) to determine the coupled effect of estuarine mixing and photobleaching on LMW and UDOM fluorescence. Permeates, except Delaware Bay samples, were more bleached at lower salinities (<16). This effect was especially noticeable for mid‐estuarine LMW organic material which was highly bleached at low salinities. Humic‐type UDOM was generally bleached less at low salinities, maximally at mid‐salinities, and less as it mixed toward the ocean end‐member. As with mixing alone experiments, the B peak showed virtually no variability in the LMW and UDOMs fraction and was not significantly bleached. The N and T peak behaved similarly to one another and were significantly bleached. PCA and PARAFAC models confirmed trends for individual peaks. A four‐dimensional PARAFAC model with pre‐ and post‐bleached as the fourth dimension showed increases in the T peak fluorescence after photobleaching (with some overlap of the B and N peak). Results from this study indicate that coupled mixing and photobleaching can alter CDOM fluorescence in ways which might increase the difficulty in using CDOM as a proxy for DOM in regional carbon cycling biogeochemical models.}, journal={Journal of Geophysical Research}, publisher={American Geophysical Union (AGU)}, author={Boyd, Thomas J. and Barham, Bethany P. and Hall, Gregory J. and Schumann, Brandon S. and Paerl, Ryan W. and Osburn, Christopher L.}, year={2010}, month={Sep} } @article{montgomery_boyd_osburn_plummer_masutani_coffin_2009, title={Desalination technology waste streams: Effect of pH and salinity on metabolism of marine microbial assemblages}, volume={249}, ISSN={0011-9164}, url={http://dx.doi.org/10.1016/j.desal.2009.03.018}, DOI={10.1016/j.desal.2009.03.018}, abstractNote={Effluents from desalination technologies may influence natural bacterial assemblages due to changes in salinity, pH, dissolved organic carbon concentration (DOC), DOC quality and cellular hydrostatic pressure. Salinity, pH, and pressure change effects on heterotrophic bacterial production (as measured by leucine incorporation) were examined in experiments with surface water from the Delaware Bay, Atlantic Ocean and Pacific Ocean. Bacterial production decreased by 57–67% when salinity of Atlantic Ocean and Delaware Bay surface water samples were increased from ambient to 60 PSU. Decreasing ambient seawater pH from 8.0 to below 5.0 with CO2 gas reduced production by 96–100%. Decreasing seawater pH by 1.5 units at 33 PSU caused equivalent inhibition to increasing salinity by 27 PSU (pH 8.0). Bacterial production in Pacific Ocean surface water pressurized for 72 h was decreased 40% by increasing salinity, when measured 1 h after decompression. However, production increased 43% with increasing salinity when measured 24 h after decompression. One explanation for these divergent effects between the 1- and 24-h sampling at ambient pH may be community adaptation. Strains amongst the natural assemblage that survived the pressurization by saturating their membrane phospholipids would likely be better adapted to compete for available nutrients under elevated salinity.}, number={2}, journal={Desalination}, publisher={Elsevier BV}, author={Montgomery, M.T. and Boyd, T.J. and Osburn, C.L. and Plummer, R.E. and Masutani, S.M. and Coffin, R.B.}, year={2009}, month={Dec}, pages={861–864} } @article{bouillon_abril_borges_dehairs_govers_hughes_merckx_meysman_nyunja_osburn_et al._2009, title={Distribution, origin and cycling of carbon in the Tana River (Kenya): a dry season basin-scale survey from headwaters to the delta}, volume={6}, ISSN={1726-4189}, url={http://dx.doi.org/10.5194/bg-6-2475-2009}, DOI={10.5194/bg-6-2475-2009}, abstractNote={Abstract. The Tana River basin (TRB) is the largest in Kenya (~120 000 km2). We conducted a survey during the dry season throughout the TRB, analyzing a broad suite of biogeochemical parameters. Biogeochemical signatures in headwater streams were highly variable. Along the middle and lower river course, total suspended matter (TSM) concentrations increased more than 30-fold despite the absence of tributary inputs, indicating important resuspension events of internally stored sediment. These resuspended sediment inputs were characterized by a lower and 14C-depleted OC content, suggesting selective degradation of more recent material during sediment retention. Masinga Dam (a large reservoir on the upper river) induced a strong nutrient retention (~50% for inorganic N, ~72% for inorganic phosphate, and ~40% for dissolved silicate). Moreover, while DOC pools and δ13C signatures were similar above, in and below the reservoir, the POC pool in Masinga surface waters was dominated by 13C-depleted phytoplankton, which contributed to the riverine POC pool immediately below the dam, but rapidly disappeared further downstream, suggesting rapid remineralization of this labile C pool in the river system. Despite the generally high turbidity, the combination of relatively high oxygen saturation levels, low δ18O signatures of dissolved O2 (all <+24.2‰), and the relatively low pCO2 values suggest that in-stream primary production was significant, even though pigment data suggest that phytoplankton makes only a minor contribution to the total POC pool in the Tana River. }, number={11}, journal={Biogeosciences}, publisher={Copernicus GmbH}, author={Bouillon, S. and Abril, G. and Borges, A. V. and Dehairs, F. and Govers, G. and Hughes, H. J. and Merckx, R. and Meysman, F. J. R. and Nyunja, J. and Osburn, C. and et al.}, year={2009}, month={Nov}, pages={2475–2493} } @article{osburn_daniel w. o'sullivan_boyd_2009, title={Increases in the longwave photobleaching of chromophoric dissolved organic matter in coastal waters}, volume={54}, ISSN={["1939-5590"]}, DOI={10.4319/lo.2009.54.1.0145}, abstractNote={Salinity effects on the photobleaching of chromophoric dissolved organic matter (CDOM) due to coastal mixing were investigated through a comparative study of surrogate and surface‐water CDOM. Suwannee River humic acid (SRHA) and ultrafiltered river dissolved organic matter (UDOM) added to mixtures of river and seawater permeates (<1 kDa) that varied in salinity from 0 to 33 to mimic coastal mixing. Surface‐water CDOM was collected from the Chesapeake Bay in January, June, and September 2002. Shortwave CDOM absorption loss (e.g., 280 nm) did not change with salinity; however, longwave CDOM absorption loss (e.g., 440 nm) often decreased by 10% to 40% with salinity. Apparent quantum yields for average absorption loss from 280 to 550 nm (ϕavg) increased with salinity for both surrogate and surface‐water CDOM, providing evidence for an effect of salinity independent of light absorption among different samples. Further, hydrogen peroxide photoproduction from UDOM increased from 15 to 368 nmol L−1 h−1 with salinity, even though pH values were circumneutral. A kinetic model demonstrated that, at circumneutral pH and iron concentrations expected for the Chesapeake Bay, photo‐Fenton chemistry could not explain the increase in hydrogen peroxide production quantum yields (ϕhp) with salinity. Using ϕavg for the SRHA and UDOM surrogates, a model of the change in surface‐water CDOM photoreactivity in the Chesapeake Bay as a function of salinity suggested additional CDOM inputs for the lower Chesapeake Bay. Because estuarine mixing increases photobleaching of longwave CDOM absorption, the modeling of absorption coefficients above 400 nm may underestimate dissolved organic matter in coastal waters.}, number={1}, journal={LIMNOLOGY AND OCEANOGRAPHY}, publisher={American Society of Limnology and Oceanography, Inc.}, author={Osburn, Christopher L. and Daniel W. O'Sullivan and Boyd, Thomas J.}, year={2009}, month={Jan}, pages={145–159} } @article{montgomery_boyd_osburn_smith_2009, title={PAH mineralization and bacterial organotolerance in surface sediments of the Charleston Harbor estuary}, volume={21}, ISSN={0923-9820 1572-9729}, url={http://dx.doi.org/10.1007/s10532-009-9298-3}, DOI={10.1007/s10532-009-9298-3}, abstractNote={Semi-volatile organic compounds (SVOCs) in estuarine waters can adversely affect biota but watershed sources can be difficult to identify because these compounds are transient. Natural bacterial assemblages may respond to chronic, episodic exposure to SVOCs through selection of more organotolerant bacterial communities. We measured bacterial production, organotolerance and polycyclic aromatic hydrocarbon (PAH) mineralization in Charleston Harbor and compared surface sediment from stations near a known, permitted SVOC outfall (pulp mill effluent) to that from more pristine stations. Naphthalene additions inhibited an average of 77% of bacterial metabolism in sediments from the more pristine site (Wando River). Production in sediments nearest the outfall was only inhibited an average of 9% and in some cases, was actually stimulated. In general, the stations with the highest rates of bacterial production also were among those with the highest rates of PAH mineralization. This suggests that the capacity to mineralize PAH carbon is a common feature amongst the bacterial assemblage in these estuarine sediments and could account for an average of 5.6% of bacterial carbon demand (in terms of production) in the summer, 3.3% in the spring (April) and only 1.2% in winter (December).}, number={2}, journal={Biodegradation}, publisher={Springer Science and Business Media LLC}, author={Montgomery, Michael T. and Boyd, Thomas J. and Osburn, Christopher L. and Smith, David C.}, year={2009}, month={Sep}, pages={257–266} } @article{osburn_retamal_vincent_2009, title={Photoreactivity of chromophoric dissolved organic matter transported by the Mackenzie River to the Beaufort Sea}, volume={115}, ISSN={0304-4203}, url={http://dx.doi.org/10.1016/j.marchem.2009.05.003}, DOI={10.1016/j.marchem.2009.05.003}, abstractNote={The photoreactivity of chromophoric dissolved organic matter (CDOM) transported to Arctic shelf environments by rivers has only recently been studied and its quantitative role in Arctic shelf biogeochemistry has received little attention. Sunlight exposure experiments were performed on CDOM collected over a three year period (2002 to 2004) from river, estuary, shelf, and gulf regions of the Western Canadian Arctic. Decreases in CDOM absorption, synchronous fluorescence (SF), and dissolved organic carbon (DOC) concentration were followed after 3 days of exposure, and in two experiments, six optical cutoff filters were used to incrementally remove ultraviolet radiation incident on the samples. Apparent quantum yields for CDOM photobleaching (AQYble) and for DOC photomineralization (AQYmin) were computed, as were two AQY spectra (ϕble and ϕmin) for the Mackenzie River and a sample from the Mackenzie Shelf. The photoreactivity of Mackenzie River CDOM was highest after break-up and peak discharge and lowest in late summer. The half-lives of CDOM and DOC were estimated at 3.7 days and 4.8 days, respectively, when Mackenzie River water was exposed to full sunlight. Photobleaching of Mackenzie River CDOM fluorescence after most UV-B wavelengths were removed increased the correlation between the river and offshore waters in the Beaufort Sea. When light attenuation from particle- and CDOM-rich river water was considered for the Mackenzie Shelf, our photodegradation models estimated around 10% loss of absorption and < 1% DOC loss, suggesting that sunlight exposure does not substantially degrade CDOM on Arctic shelves.}, number={1-2}, journal={Marine Chemistry}, publisher={Elsevier BV}, author={Osburn, Christopher L. and Retamal, Leira and Vincent, Warwick F.}, year={2009}, month={Jun}, pages={10–20} } @article{prairie_salm_saros_fritz_osburn_reineke_2009, title={Phytoplankton productivity across prairie saline lakes of the Great Plains (USA): a step toward deciphering patterns through lake classification models}, volume={66}, DOI={10.1139/f09-083}, abstractNote={ We investigated patterns of primary production across prairie saline lakes in the central and northern Great Plains of the United States. Based on comparative lake sampling in 2004, seasonal predictors of algal primary productivity were identified within subsets of similar lakes using a combination of Akaike’s information criterion (AIC) and classification and regression trees (CART). These models indicated complex patterns of nutrient limitation by nitrogen (N), phosphorus (P), and iron (Fe) within different lake groups. Nutrient enrichment assays (control, + Fe, + N, + P, + N + P) were performed in spring and summer of 2006 to determine if phytoplankton in selected lakes followed predicted patterns of nutrient limitation. Both the comparative lake sampling and experimental results indicated that N limitation was widespread in these prairie lakes, with evidence for secondary P limitation in certain lakes. In the experiments, iron did not stimulate primary production. Our results suggest that given the diverse geochemical nature of these lakes, classification models that separate saline lakes into subsets may be an effective method for improving predictions of algal production. }, number={9}, journal={Can. J. Fish. Aquat. Sci.}, publisher={Canadian Science Publishing}, author={Prairie, Yves and Salm, Courtney R. and Saros, Jasmine E. and Fritz, Sherilyn C. and Osburn, Christopher L. and Reineke, David M.}, year={2009}, month={Sep}, pages={1435–1448} } @article{vallières_retamal_ramlal_osburn_vincent_2008, title={Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean}, volume={74}, DOI={10.1016/j.jmarsys.2007.12.002}, abstractNote={Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 105 cells mL− 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL− 1. There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea. Size-fractionated bacterial production, as measured by 3H–leucine uptake, varied from 76 to 416 ng C L− 1 h− 1. The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea. Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, PCO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO2 at increasing rates as the arctic climate continues to warm.}, number={3-4}, journal={Journal of Marine Systems}, publisher={Elsevier BV}, author={Vallières, Catherine and Retamal, Leira and Ramlal, Patricia and Osburn, Christopher L. and Vincent, Warwick F.}, year={2008}, pages={756–773} } @inbook{boyd_smith_apple_hamdan_osburn_montgomery_2008, place={Hauppauge, NY}, title={Evaluating PAH Biodegradation Relative to Total Bacterial Carbon Demand in Coastal Ecosystems: Are PAHs Truly Recalcitrant?}, booktitle={Microbial Ecology Research Trends}, publisher={NOVA Science Publishers Inc}, author={Boyd, T.J. and Smith, D.C. and Apple, J.K. and Hamdan, L.J. and Osburn, C.L. and Montgomery, M.T}, editor={Van Dijk, T.Editor}, year={2008}, pages={1–38} } @article{montgomery_osburn_furukawa_gieskes_2008, title={Increased Capacity for Polycyclic Aromatic Hydrocarbon Mineralization in Bioirrigated Coastal Marine Sediments}, volume={12}, DOI={10.1080/10889860802060469}, abstractNote={ABSTRACT Bioirrigation of marine sediments by benthic infauna has the potential to increase both the rate and depth of bacterial mineralization of polycyclic aromatic hydrocarbons (PAHs) by recirculating oxygenated bottom water into sediment burrows. Rates of heterotrophic bacterial production and mineralization of PAHs (naphthalene, phenanthrene, and fluoranthene) were measured in sections of sediment cores sampled from stations in San Diego Bay. Data suggest that rates of PAH biodegradation and bacterial heterotrophy were influenced by bioirrigation by benthic infauna. PAH mineralization and heterotrophic production were higher in core sections where sulfide was not detected relative to core sections containing sulfide. Depth-integrated capacity of the upper 17 cm of sediment to mineralize PAHs was 4 to 10 times higher at the station with bioirrigation coefficients that increased with depth. Remedial dredging of sediments to remove contaminant mass (and presumable lower ecological risk) will also remove benthic infauna. Removal of infauna and the subsequent lowering of bioirrigation in surface sediments would be expected to lower the capacity of intrinsic PAH bioremediation. This could cause local increases in ambient PAH concentration and consequently increase the ecological risk at the site and potentially degrade the health of the ecosystem by removing a sink for PAHs.}, number={2}, journal={Bioremediation Journal}, publisher={Informa UK Limited}, author={Montgomery, Michael T. and Osburn, Christopher L. and Furukawa, Yoko and Gieskes, Joris M.}, year={2008}, month={May}, pages={98–110} } @article{tzortziou_neale_osburn_megonigal_maie_jaffé_2008, title={Tidal marshes as a source of optically and chemically distinctive colored dissolved organic matter in the Chesapeake Bay}, volume={53}, DOI={10.4319/lo.2008.53.1.0148}, abstractNote={The role of tidal marshes as a source of dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) for adjacent estuarine waters was studied in the Rhode River subestuary of the Chesapeake Bay. Water in a tidal creek draining brackish, high‐elevation marshes was sampled every hour during several semidiurnal tidal cycles in order to examine the tidal exchange of dissolved organic matter (DOM). Water leaving the marsh during ebbing tide was consistently enriched in DOC compared to water entering the marsh during flooding tide. There was a net DOC export from the marsh to the estuary during seasons of both low and high marsh plant biomass. Optical analysis demonstrated that, in addition to contributing to the carbon budgets, the marsh had a strong influence on the estuary’s CDOM dynamics. Marsh‐exported CDOM had optical properties that were consistently and markedly different from those of CDOM in the adjacent estuary. Specifically, marsh CDOM had: (1) considerably stronger absorption, (2) larger DOC‐specific absorption, (3) lower exponential spectral slope, (4) larger fluorescence signal, (5) lower fluorescence per unit absorbance, and (6) higher fluorescence at wavelengths >400 nm. These optical characteristics are indicative of relatively complex, high‐molecular‐weight, aromatic‐rich DOM, and this was confirmed by results of molecular‐weight‐distribution analysis. Our findings illustrate the importance of tidal marshes as sources of optically and chemically distinctive dissolved organic compounds, and their influence on CDOM dynamics, DOC budgets, and, thus, photochemical and biogeochemical processes, in adjacent estuarine ecosystems.}, number={1}, journal={Limnol. Oceangr.}, publisher={Wiley-Blackwell}, author={Tzortziou, Maria and Neale, Patrick J. and Osburn, Christopher L. and Megonigal, J. Patrick and Maie, Nagamitsu and Jaffé, Rudolf}, year={2008}, pages={148–159} } @article{tzortziou_osburn_neale_2007, title={Photobleaching of Dissolved Organic Material from a Tidal Marsh-Estuarine System of the Chesapeake Bay†}, volume={83}, DOI={10.1111/j.1751-1097.2007.00142.x}, abstractNote={ABSTRACTWetlands and tidal marshes in the Rhode River estuary of the Chesapeake Bay act as important sources of dissolved organic carbon and strongly absorbing dissolved organic matter (DOM) for adjacent estuarine waters. The effects of solar exposure on the photochemical degradation of colored DOM (CDOM) were examined for material derived from different sources (estuarine and freshwater parts of the Rhode River, sub‐watershed stream, marshes) in this estuarine ecosystem. Consistent with changes in fluorescence emission, absorption loss upon exposure to different portions of the solar spectrum (i.e. different long‐pass cut‐off filters) occurred across the entire spectrum but the wavelength of maximum photobleaching decreased as the cut‐off wavelength of the filter decreased. Our results illustrate that solar exposure can cause either an increase or a decrease in the CDOM absorption spectral slope, SCDOM, depending on the spectral quality of irradiation and, thus, on the parameters (e.g. atmospheric composition, concentration of UV‐absorbing water constituents) that affect the spectral characteristics of the light to which CDOM is exposed. We derived a simple spectral model for describing the effects of solar exposure on CDOM optical quality. The model accurately, and consistently, predicted the observed dependence of CDOM photobleaching on the spectral quality of solar exposure.}, number={4}, journal={Photochemistry and Photobiology}, publisher={Wiley-Blackwell}, author={Tzortziou, Maria and Osburn, Christopher L. and Neale, Patrick J.}, year={2007}, month={Jun}, pages={782–792} } @article{osburn_st-jean_2007, title={The use of wet chemical oxidation with high-amplification isotope ratio mass spectrometry (WCO-IRMS) to measure stable isotope values of dissolved organic carbon in seawater}, volume={5}, DOI={10.4319/lom.2007.5.296}, abstractNote={Few measurements of the carbon stable isotope value (δ13C) of marine dissolved organic carbon (DOC), the largest pool of reduced carbon in the ocean, have been made because of analytical obstacles due to the interference of halides and the low amount of DOC in seawater. By using concentrated persulfate in a wet chemical oxidation organic carbon analyzer coupled to an isotope ratio mass spectrometry (WCO‐IRMS) the analytical obstacles are overcome. Key to this method is reducing the persulfate blank and increasing the IRMS signal with larger amplifier gain resistors. After these simple modifications, a 2 mL sample provides enough signal to make precise measurements of DOC concentration and δ13C value on up to 15 samples per day. Sodium persulfate (1.68 mol L−1) is cleaned by pre‐heating and sparging with ultrahigh purity helium. In the WCO analyzer, 6 mL cleaned persulfate is added to 2 mL sample at 98°C for 8.5 min to completely oxidize DOC to CO2. After quantitative measurement by nondispersive IR, the gases contained in the exhaust are swept through a cleanup reactor, separated by a GC column and introduced to the IRMS for δ13C measurement. Complete recovery of the DOC and δ13C values was confirmed with two DOC standards added individually to seawater. IRMS precision was confirmed by measuring a range of sea water samples. On several coastal water samples measured using this system, δ13C‐DOC values ranging from −22‰ to −25‰. These results were consistent with published reports of seawater δ13C‐DOC using other methods.}, number={10}, journal={Limnol. Oceanogr. Methods}, publisher={Wiley-Blackwell}, author={Osburn, Christopher L. and St-Jean, Gilles}, year={2007}, month={Oct}, pages={296–308} } @article{retamal_vincent_martineau_osburn_2007, title={Comparison of the optical properties of dissolved organic matter in two river-influenced coastal regions of the Canadian Arctic}, volume={72}, ISSN={0272-7714}, url={http://dx.doi.org/10.1016/j.ecss.2006.10.022}, DOI={10.1016/j.ecss.2006.10.022}, abstractNote={The optical characteristics of coloured dissolved organic matter (CDOM) were analyzed in the Great Whale River and adjacent Hudson Bay (55° N, 77° W) in the eastern Canadian Low Arctic, and in the Mackenzie River and adjacent Beaufort Sea in the western Canadian High Arctic (70° N, 133° W). Sampling was during ice-free open water conditions. Both rivers contained high concentrations of dissolved organic carbon (3 and 6 mg DOC l−1 in the Great Whale River and Mackenzie River, respectively) and CDOM (a320 of 11 and 14 m−1), resulting in a substantial load of organic matter to their coastal seas. There were pronounced differences in the CDOM characteristics of the two rivers, notably in their synchronous fluorescence scans (SFS). The latter showed that the Mackenzie River was depleted in humic materials, implying a more mature catchment relative to the younger, more recently glaciated Great Whale River system. SFS spectra had a similar shape across the freshwater–saltwater transition zone of the Great Whale plume, and DOC was linearly related to salinity implying conservative mixing and no loss by flocculation or biological processes across the salt front. In contrast, there were major differences in SFS spectral shape from the Mackenzie River to the freshwater-influenced coastal ocean, with a marked decrease in the relative importance of fulvic and humic acid materials. The SFS spectra for the coastal Beaufort Sea in September–October strongly resembled those recorded for the Mackenzie River during the high discharge, CDOM-rich, snowmelt period in June, but with some loss of autochthonous materials. These results are consistent with differences in freshwater residence time between the Mackenzie River and Great Whale River coastal ocean systems. Models of arctic continental shelf responses to present and future climate regimes will need to consider these striking regional differences in the organic matter content, biogeochemistry and optics between waters from different catchments and different inshore hydrodynamic regimes.}, number={1-2}, journal={Estuarine, Coastal and Shelf Science}, publisher={Elsevier BV}, author={Retamal, Leira and Vincent, Warwick F. and Martineau, Christine and Osburn, Christopher L.}, year={2007}, month={Mar}, pages={261–272} } @article{boyd_osburn_johnson_birgl_coffin_2006, title={Compound-Specific Isotope Analysis Coupled with Multivariate Statistics to Source-Apportion Hydrocarbon Mixtures}, volume={40}, DOI={10.1021/es050975p}, abstractNote={Compound Specific Isotope Analysis (CSIA) has been shown to be a useful tool for assessing biodegradation, volatilization, and hydrocarbon degradation. One major advantage of this technique is that it does not rely on determining absolute or relative abundances of individual components of a hydrocarbon mixture which may change considerably during weathering processes. However, attempts to use isotopic values for linking sources to spilled or otherwise unknown hydrocarbons have been hampered by the lack of a robust and rigorous statistical method for testing the hypothesis that two samples are or are not the same. Univariate tests are prone to Type I and Type II error, and current means of correcting error make hypothesis testing of CSIA source-apportionment data problematic. Multivariate statistical tests are more appropriate for use in CSIA data. However, many multivariate statistical tests require high numbers of replicate measurements. Due to the high precision of IRMS instruments and the high cost of CSIA analysis, it is impractical, and often unnecessary, to perform many replicate analyses. In this paper, a method is presented whereby triplicate CSIA information can be projected in a simplified data-space, enabling multivariate analysis of variance (MANOVA) and highly precise testing of hypotheses between unknowns and putative sources. The method relies on performing pairwise principal components analysis (PCA),then performing a MANOVA upon the principal component variables (for instance, three, using triplicate analyses) which capture most of the variability in the original data set. A probability value is obtained allowing the investigator to state whether there is a statistical difference between two individual samples. A protocol is also presented whereby results of the coupled pairwise PCA-MANOVA analysis are used to down-select putative sources for other analysis of variance methods (i.e., PCA on a subset of the original data) and hierarchical clustering to look for relationships among samples which are not significantly different. A Monte Carlo simulation of a 10 variable data set; tanks used to store, distribute, and offload fuels from Navy vessels; and a series of spilled oil samples and local tug boats from Norfolk, VA (U.S.A.) were subjected to CSIA and the statistical analyses described in this manuscript, and the results are presented. The analysis techniques described herein combined with traditional forensic analyses provide a collection of tools suitable for source-apportionment of hydrocarbons and any organic compound amenable to GC-combustion-IRMS.}, number={6}, journal={Environ. Sci. Technol.}, publisher={American Chemical Society (ACS)}, author={Boyd, Thomas J. and Osburn, Christopher L. and Johnson, Kevin J. and Birgl, Keri B. and Coffin, Richard B.}, year={2006}, month={Mar}, pages={1916–1924} } @book{walker_osburn_boyd_hamdan_coffin_montgomery_smith_li_monteil_hawari_2006, place={Washington DC}, title={Mineralization of 2,4,6-Trinitrotoleune (TNT) in Coastal Waters and Sediments}, url={http://dx.doi.org/10.21236/ada456842}, DOI={10.21236/ada456842}, abstractNote={Abstract : Mineralization rates of 14C-TNT, -DNT, and -DAT were measured in surface sediments, with depth in sediment cores, and in the water column during 12 research cruises over the past 4 years in the San Francisco Bay, Chesapeake Bay, and Hawaii. Mineralization rates were also compared to uptake and incorporation rates of TNT, DNT, and DAT into the natural microbial assemblage. In general, the bacterial mineralizations rates were similar, or an order of magnitude faster, than those for organic hydrocarbons measured at the same time. Using seawater sampled from a historical UXO field, we found that while bacterial mineralization was rapid (>1 ug L-1 d-1, unfiltered water in dark), photodegradation was even faster (16 ug L-1 d-1, filtered water in light) and the combination of light and unfiltered water was greater than the sum of the two rates (103 ug L-1 d-1), suggesting either that the presence of active phytoplankton is important or photodegradation enhances bacterial mineralization.}, number={NRL/FR/6114–06-10135NRL/FR/6114--06-10135}, institution={Defense Technical Information Center}, author={Walker, S. W. and Osburn, C. L. and Boyd, T. J. and Hamdan, L. J. and Coffin, R. B. and Montgomery, M. T. and Smith, J. P. and Li, Q. X. and Monteil, F. and Hawari, J.}, year={2006}, month={Aug} } @article{o'sullivan_neale_coffin_boyd_osburn_2005, title={Photochemical production of hydrogen peroxide and methylhydroperoxide in coastal waters}, volume={97}, DOI={10.1016/j.marchem.2005.04.003}, abstractNote={Hydrogen peroxide (H2O2) has been observed in significant concentrations in many natural waters. Because hydrogen peroxide can act as an oxidant and reductant, it participates in an extensive suite of reactions in surface waters. Hydrogen peroxide is produced as a secondary photochemical product of chromophoric dissolved organic matter (CDOM) photolysis. Apparent quantum yields for the photochemical production of hydrogen peroxide were determined in laboratory irradiations of filtered surface waters from several locations in the Chesapeake Bay and in Arctic coastal waters with varying levels of CDOM. The apparent quantum yield for H2O2 decreases by about an order of magnitude from 280 nm to 500 nm, and the majority of H2O2 production occurs at wavelengths less than 340 nm. The apparent quantum yield for H2O2 production at 290 nm ranged from 4.2 × 10− 4 to 2.1 × 10− 6 mol H2O2 (mol photons)− 1 from freshwater to marine waters. A linear relationship was found between the production of H2O2 and change in CDOM absorbance characterized as photobleaching (loss of absorbance). No significant relationship was observed between DOC concentration and peroxide production. Methylhydroperoxide (CH3O2H) was the only short chain peroxide produced during the irradiations, and its production is at least an order magnitude less than that of hydrogen peroxide. Peroxide production was greatest in waters containing significant amounts of terrigenous C in the form of humic substances. Surface waters whose synchronous fluorescence spectra indicated the presence of polyaromatic and/or extensive conjugated compounds exhibited the greatest peroxide production. CDOM photobleaching is not significantly linked to apparent quantum yields for peroxide production.}, number={1-2}, journal={Marine Chemistry}, publisher={Elsevier BV}, author={O'Sullivan, Daniel W. and Neale, Patrick J. and Coffin, Richard B. and Boyd, Thomas J. and Osburn, Christopher L.}, year={2005}, month={Oct}, pages={14–33} } @article{maloney_morris_moses_osburn_2005, title={The Role of Iron and Dissolved Organic Carbon in the Absorption of Ultraviolet Radiation in Humic Lake Water}, volume={75}, DOI={10.1007/s10533-005-1675-3}, number={3}, journal={Biogeochemistry}, publisher={Springer Science \mathplus Business Media}, author={Maloney, Kelly O. and Morris, Donald P. and Moses, Carl O. and Osburn, Christopher L.}, year={2005}, month={Sep}, pages={393–407} } @book{montgomery_osburn_2004, place={Washington DC}, title={Bacterial metabolism, aromatic biodegradation, and lignin biogeochemistry in sediment cores from Pearl Harbor, Hawai’i}, number={NRL/FR/6114--04-10,077}, institution={Naval Research Laboratory}, author={Montgomery, M.T. and Osburn, C.L.}, year={2004} } @article{boyd_osburn_2004, title={Changes in CDOM fluorescence from allochthonous and autochthonous sources during tidal mixing and bacterial degradation in two coastal estuaries}, volume={89}, DOI={10.1016/j.marchem.2004.02.012}, abstractNote={Chromophoric dissolved organic matter (CDOM) was collected and concentrated using 1 kDa cutoff tangential flow filtration (TFF) from marine (∼33 salinity), mid-estuarine (∼15 salinity), and freshwater (<1 salinity) portions of the Chesapeake and San Francisco Bays. Natural bacterioplankton were also collected during the same transects on 0.22-μm pore size filters. TFF permeates from freshwater, mid-estuarine and marine stations were used to create a series of salinity samples ranging from 0 to 33 by increments of 3. Freshwater CDOM was added in the same proportion to each salinity sample to determine changes in spectral signals during simulated estuarine mixing. A series of incubations was conducted in which concentrated CDOM was added to TFF permeates (<1 kDa, low fluorescence) in a nine-membered matrix such that each station's CDOM was added to each station's TFF permeate. Each incubation was then inoculated with a filter from its respective collection location. Subsamples from bacterial incubations were collected at various times and analyzed by high resolution three-dimensional fluorescence excitation–emission spectroscopy (EEMs) to determine if changes in ionic strength encountered during estuarine mixing affect the bioavailability and optical properties of CDOM. Five EEMs peaks were identified for each mixing experiment and microbial subsample; Exmax: 330–350 nm/ Emmax: 420–480 nm, Exmax: 250–260 nm/ Emmax: 380–480 nm, Exmax: 310–320 nm/ Emmax: 380–420 nm, Exmax: 270–280 nm/ Emmax: 300–320 nm, and Exmax: 270–280 nm/ Emmax: 320–350 nm. These peak ratios were monitored over the time course of the experiment. Changes in several spectral properties during the simulated estuarine mixing were observed indicating CDOM conformational changes as it moves through the estuary. We hypothesized these changes may impact the biodegradability of CDOM as it moves from upland sources to the coastal ocean. Changes in DOC concentration during incubation indicated that allochthonous CDOM was a more utilizable substrate for estuarine and marine bacteria. There were also differences in peak ratios observed during incubation with allochthonous and autochthonous CDOM. There were Emmax peak shifts dependent on the source of CDOM and bacteria, with more red shifting (toward higher wavelengths) in upper reaches of the estuary and more blue-shifting at the oceanic end-member. We conclude that bacterial degradation of specific components of autochthonous and allochthonous CDOM may impact the spectral characteristics observed throughout an estuary and that CDOM optical properties are partially a function of the CDOM's origin and mixing history.}, number={1-4}, journal={Marine Chemistry}, publisher={Elsevier BV}, author={Boyd, Thomas J and Osburn, Christopher L}, year={2004}, month={Oct}, pages={189–210} } @book{montgomery_osburn_2003, place={Washington, DC}, title={Depth profile of bacterial metabolism and PAH biodegradation in bioturbated and unbioturbated marine sediments}, number={NRL/FR/6114--03-10.057}, institution={Naval Research Laboratory}, author={Montgomery, M.T. and Osburn, C.L.}, year={2003} } @article{osburn_morris_2003, title={Photochemistry of chromophoric dissolved organic matter in natural waters}, DOI={10.1039/9781847552266-00185}, journal={UV Effects in Aquatic Organisms and Ecosystems}, publisher={Royal Society of Chemistry}, author={Osburn, Christopher L. and Morris, Donald P.}, year={2003}, pages={185–218} } @article{montgomery_osburn_boyd_smith_mueller_2002, title={Seasonal Succession of the PAH-Mineralizing Bacteria in Creosote-Impacted Intertidal Sediments}, volume={11}, ISSN={1532-0383 1549-7887}, url={http://dx.doi.org/10.1080/20025891108040}, DOI={10.1080/20025891108040}, abstractNote={Michael T. Montgomery, Chris L. Osburn, and Thomas J. Boyd—Naval Research Laboratory, Code 6115, 4555 Overlook Avenue, Washington, DC 20375, USA, mtm@ccf.nrl.navy.mil, Telephone: (202) 404-6419, Fax: (202) 404-8515; David C. Smith—Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA, dcsmith@gso.uri.edu, Telephone: (401) 874-6172, Fax: (401) 874-6240; James G. Mueller—URS/Dames and Moore, 1701 Golf Road, Tower One, Suite 1000, Rolling Meadows, IL, 60008, USA, Jim_Mueller@URSCorp.com, Telephone: (847) 228-0707, Fax: (847) 228-1115}, number={3}, journal={Soil and Sediment Contamination: An International Journal}, publisher={Informa UK Limited}, author={Montgomery, Michael T. and Osburn, Chris L. and Boyd, Thomas J. and Smith, David C. and Mueller, James G.}, year={2002}, month={May}, pages={479–479} } @article{osburn_zagarese_morris_hargreaves_cravero_2001, title={Calculation of spectral weighting functions for the solar photobleaching of chromophoric dissolved organic matter in temperate lakes}, volume={46}, DOI={10.4319/lo.2001.46.6.1455}, abstractNote={The effect of solar radiation on the dissolved absorption coefficient (λCDOM[λ]), which reflects the concentration of chromophoric dissolved organic matter (CDOM), was investigated in several lakes near Bariloche, Argentina and in northeastern Pennsylvania, USA. Samples of 0.2 µm filtered lake water were exposed in quartz tubes to different portions of the solar spectrum using optical cutoff filters to remove parts of the ultraviolet (UV) region of the solar spectrum. Changes in the spectral absorption in these samples and the absorbed incident energy were used to calculate spectral weighting functions (SWFs) for the photobleaching (PB) of CDOM. PB was measured as the loss of αCDOM[λ] (the αCDOM[λ] was averaged from 280 to 500 nm) per unit absorbed energy. CDOM from humic and clear lakes, as well as from a Sphagnum bog and an algal culture, was used in the experiments covering a wide range of carbon sources. We used an iterative, nonlinear optimization method to fit the measured results to a simple exponential function in order to generate each SWF. Comparing individual SWFs calculated for various CDOM sources, we computed a summary SWF from the experiments using epilimnial CDOM from our study lakes. Our summary SWF was able to explain 80‐90% of the observed variance in our exposure experiments, and we were able to predict PB results obtained for other Argentine lakes (mean error 14.5%). Finally, we calculated that the effect of UV‐B radiation on PB was small (<20% of total decrease in the absorption coefficient) compared to UVA and blue light radiation. This suggested that increased UV‐B radiation due to stratospheric ozone depletion would not greatly increase the photobleaching of whole water column CDOM in Patagonian lakes (<10%).}, number={6}, journal={Limnol. Oceanogr.}, publisher={Wiley-Blackwell}, author={Osburn, Christopher L. and Zagarese, Horacio E. and Morris, Donald P. and Hargreaves, Bruce R. and Cravero, Walter E.}, year={2001}, month={Aug}, pages={1455–1467} } @article{osburn_morris_thorn_moeller_2001, title={Chemical and optical changes in freshwater dissolved organic matter exposed to solar radiation}, volume={54}, ISSN={0168-2563}, url={http://dx.doi.org/10.1023/a:1010657428418}, DOI={10.1023/a:1010657428418}, abstractNote={We studied the chemical and optical changes inthe dissolved organic matter (DOM) from twofreshwater lakes and a Sphagnum bog afterexposure to solar radiation. Stable carbonisotopes and solid-state 13C-NMR spectraof DOM were used together with optical andchemical data to interpret results fromexperimental exposures of DOM to sunlight andfrom seasonal observations of two lakes innortheastern Pennsylvania. Solar photochemicaloxidation of humic-rich bog DOM to smaller LMWcompounds and to DIC was inferred from lossesof UV absorbance, optical indices of molecularweight and changes in DOM chemistry. Experimentally, we observed a 1.2‰ enrichment in δ13$C and a 47% loss in aromaticC functionality in bog DOM samples exposed tosolar UVR. Similar results were observed inthe surface waters of both lakes. In latesummer hypolimnetic water in humic LakeLacawac, we observed 3 to 4.5‰enrichments in δ13C and a 30% increase inaromatic C relative to early spring valuesduring spring mixing. These changes coincidedwith increases in molecular weight and UVabsorbance. Anaerobic conditions of thehypolimnion in Lake Lacawac suggest thatmicrobial metabolism may be turning overallochthonous C introduced during springmixing, as well as autochthonous C. Thismetabolic activity produces HMW DOM during thesummer, which is photochemically labile andisotopically distinct from allochthonous DOM orautochthonous DOM. These results suggest bothphotooxidation of allochthonous DOM in theepilimnion and autotrophic production of DOM bybacteria in the hypolimnion cause seasonaltrends in the UV absorbance of lakes.}, number={3}, journal={Biogeochemistry}, publisher={Springer Science and Business Media LLC}, author={Osburn, Christopher L. and Morris, Donald P. and Thorn, Kevin A. and Moeller, Robert E.}, year={2001}, month={Jul}, pages={251–278} } @article{bralower_cobabe_clement_sliter_osburn_longoria_1999, title={The record of global change in mid-Cretaceous (Barremian-Albian) sections from the Sierra Madre, Northeastern, Mexico}, volume={29}, number={4}, journal={Journal of Foraminiferal Research}, author={Bralower, T.J. and CoBabe, E.A. and Clement, B. and Sliter, W.V. and Osburn, C.L. and Longoria, J.}, year={1999}, pages={418–437} }