@article{paerl_hall_hounshell_rossignol_barnard_luettich jr_rudolph_osburn_bales_harding jr_2023, 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={164}, ISSN={["1573-515X"]}, DOI={10.1007/s10533-021-00770-2}, 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={1}, journal={BIOGEOCHEMISTRY}, author={Paerl, Hans W. and Hall, Nathan S. and Hounshell, Alexandria G. and Rossignol, Karen L. and Barnard, Malcolm A. and Luettich Jr, Richard A. and Rudolph, Jacob C. and Osburn, Christopher L. and Bales, Jerad and Harding Jr, Lawrence W.}, year={2023}, month={May}, pages={257–276} }
 @article{han_aziz_del giudice_hall_obenour_2021, title={Exploring nutrient and light limitation of algal production in a shallow turbid reservoir}, volume={269}, ISSN={["1873-6424"]}, DOI={10.1016/j.envpol.2020.116210}, abstractNote={Harmful algal blooms are increasingly recognized as a threat to the integrity of freshwater reservoirs, which serve as water supplies, wildlife habitats, and recreational attractions. While algal growth and accumulation is controlled by many environmental factors, the relative importance of these factors is unclear, particularly for turbid eutrophic systems. Here we develop and compare two models that test the relative importance of vertical mixing, light, and nutrients for explaining chlorophyll-a variability in shallow (2–3 m) embayments of a eutrophic reservoir, Jordan Lake, North Carolina. One is a multiple linear regression (statistical) model and the other is a process-based (mechanistic) model. Both models are calibrated using a 15-year data record of chlorophyll-a concentration (2003–2018) for the seasonal period of cyanobacteria dominance (June–October). The mechanistic model includes a novel representation of vertical mixing and is calibrated in a Bayesian framework, which allows for data-driven inference of important process rates. Both models show that chlorophyll-a concentration is much more responsive to nutrient variability than mixing, light, or temperature. While both models explain approximately 60% of the variability in chlorophyll-a, the mechanistic model is more robust in cross-validation and provides a more comprehensive assessment of algal drivers. Overall, these models indicate that nutrient reductions, rather than changes in mixing or background turbidity, are critical to controlling cyanobacteria in a shallow eutrophic freshwater system.}, journal={ENVIRONMENTAL POLLUTION}, author={Han, Yue and Aziz, Tarek N. and Del Giudice, Dario and Hall, Nathan S. and Obenour, Daniel R.}, year={2021}, month={Jan} }
 @article{hounshell_fegley_hall_osburn_paerl_2021, title={Riverine Discharge and Phytoplankton Biomass Control Dissolved and Particulate Organic Matter Dynamics over Spatial and Temporal Scales in the Neuse River Estuary, North Carolina}, volume={5}, ISSN={["1559-2731"]}, DOI={10.1007/s12237-021-00955-w}, abstractNote={Estuaries function as important transporters, transformers, and producers of organic matter (OM). Along the freshwater to saltwater gradient, the composition of OM is influenced by physical and biogeochemical processes that change spatially and temporally, making it difficult to constrain OM in these ecosystems. In addition, many of the environmental parameters (temperature, precipitation, riverine discharge) controlling OM are expected to change due to climate change. To better understand the environmental drivers of OM quantity (concentration) and quality (absorbance, fluorescence), we assessed both dissolved OM (DOM) and particulate OM (POM) spatially, along the freshwater to saltwater gradient and temporally, for a full year. We found seasonal differences in salinity throughout the estuary due to elevated riverine discharge during the late fall to early spring, with corresponding changes to OM quantity and quality. Using redundancy analysis, we found DOM covaried with salinity (adjusted r2 = 0.35, 0.41 for surface and bottom), indicating terrestrial sources of DOM in riverine discharge were the dominant DOM sources throughout the estuary, while POM covaried with environmental indictors of terrestrial sources (turbidity, adjusted r2 = 0.16, 0.23 for surface and bottom) as well as phytoplankton biomass (chlorophyll-a, adjusted r2 = 0.25, 0.14 for surface and bottom). Responses in OM quantity and quality observed during the period of elevated discharge were similar to studies assessing OM quality following extreme storm events suggesting that regional changes in precipitation, as predicted by climate change, will be as important in changing the estuarine OM pool as episodic storm events in the future.}, journal={ESTUARIES AND COASTS}, author={Hounshell, Alexandria G. and Fegley, Stephen R. and Hall, Nathan S. and Osburn, Christopher L. and Paerl, Hans W.}, year={2021}, month={May} }
 @article{katin_del giudice_hall_paerl_obenour_2021, title={Simulating algal dynamics within a Bayesian framework to evaluate controls on estuary productivity}, volume={447}, ISSN={["1872-7026"]}, DOI={10.1016/j.ecolmodel.2021.109497}, abstractNote={The Neuse River Estuary (North Carolina, USA) is a valuable ecosystem that has been affected by the expansion of agricultural and urban watershed activities over the last several decades. Eutrophication, as a consequence of enhanced anthropogenic nutrient loadings, has promoted high phytoplankton biomass, hypoxia, and fish kills. This study compares and contrasts three models to better understand how nutrient loading and other environmental factors control phytoplankton biomass, as chl-a, over time. The first model is purely statistical, while the second model mechanistically simulates both chl-a and nitrogen dynamics, and the third additionally simulates phosphorus. The models are calibrated to a multi-decadal dataset (1997–2018) within a Bayesian framework, which systematically incorporates prior information and accounts for uncertainties. All three models explain over one third of log-transformed chl-a variability, with the mechanistic models additionally explaining the majority of the variability in bioavailable nutrients (R2 > 0.5). By disentangling the influences of riverine nutrient concentrations, flows, and loadings on estuary productivity we find that concentration reductions, rather than total loading reductions, are the key to controlling estuary chl-a levels. The third model indicates that the estuary, even in its upstream portion, is rarely phosphorus limited, and will continue to be mostly nitrogen limited even under a 30% phosphorus reduction scenario. This model also predicts that a 10% change in nitrogen loading (flow held constant) will produce an approximate 4.3% change in estuary chl-a concentration, while the statistical model suggests a larger (10%) effect. Overall, by including a more detailed representation of environmental factors controlling algal growth, the mechanistic models generate chl-a forecasts with less uncertainty across a range of nutrient loading scenarios. Methodologically, this study advances the use of Bayesian methods for modeling the eutrophication dynamics of an estuarine system over a multi-decadal period.}, journal={ECOLOGICAL MODELLING}, author={Katin, Alexey and Del Giudice, Dario and Hall, Nathan S. and Paerl, Hans W. and Obenour, Daniel R.}, year={2021}, month={May} }
 @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} }
 @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{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={Abstract}, 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{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} }