@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_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{oviedo-vargas_dierick_genereux_oberbauer_2016, title={Chamber measurements of high CO2 emissions from a rainforest stream receiving old C-rich regional groundwater}, volume={130}, ISSN={["1573-515X"]}, DOI={10.1007/s10533-016-0243-3}, abstractNote={Carbon emissions from fluvial systems are a key component of local and regional carbon cycles. We used floating chambers to investigate the CO2 flux from stream water to air ( $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ ) in the Arboleda, a stream in the lowland rainforest of Costa Rica, fed partly by old regional groundwater high in dissolved inorganic carbon (DIC). Drifting and static chambers showed $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ averaging 35.5 and 72.7 μmol C m−2 s−1, respectively, bracketing the previously-published $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ value of 56 μmol C m−2 s−1 obtained using tracer methods in this stream. These values are much higher than most $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ data in the literature and reflect a large flux of deep crustal (non-biogenic) CO2 out of the Arboleda, a flux that does not represent a component of ecosystem respiration. Static chambers appeared to overestimate $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ by creating artificial turbulence, while drifting chambers may have underestimated $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ by under-sampling areas of potentially high gas exchange (e.g., riffles around coarse woody debris obstructions). Both static and drifting chambers revealed high spatial heterogeneity in $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ at the scale of 5–30 m reaches. Some observed temporal trends were localized, e.g., among three reaches with repeated measurements through the wet and dry seasons, (1) only the reach located between the other two showed significantly lower $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ during the dry season, and (2) the highest and lowest $${\text{f}}_{{{\text{CO}}_{ 2} }}$$ were consistently observed in the reaches farthest upstream and downstream, respectively. Streams like the Arboleda receiving significant inputs of high-DIC regional groundwater merit additional study as hotspots for C emissions from terrestrial ecosystems.}, number={1-2}, journal={BIOGEOCHEMISTRY}, author={Oviedo-Vargas, Diana and Dierick, Diego and Genereux, David P. and Oberbauer, Steven F.}, year={2016}, month={Oct}, pages={69–83} } @article{oviedo-vargas_royer_2015, title={The role of dissolved organic nitrogen in a nitrate-rich agricultural stream}, volume={44}, number={2}, journal={Journal of Environmental Quality}, author={Oviedo-Vargas, D. and Royer, T. V.}, year={2015}, pages={668–675} }