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Spatial variability in denitrification rates in an Oregon tidal salt marsh
Michael, L., J. Moon, A. Nahlik, S. Fennessy, Ted DeWitt, J. Stecher, AND K. Naithani. Spatial variability in denitrification rates in an Oregon tidal salt marsh. Society of Wetland Scientists Annual Meeting, Corpus Christi, TX, May 31 - June 04, 2016.
EPA scientists at NHEERL/WED and colleagues at University of Arkansas and Kenyon College are developing ecological models to estimate how changes in upland land use, wetland habitat configuration, and climate affect the capacity of tidal wetlands to remove nitrogen from surface and ground waters. Nitrogen removal is an important water-purification ecosystem service of wetlands, and development of these models may help communities obtain cleaner estuarine water (i.e., less enriched by nutrients) by virtue of maintaining, restoring or expanding tidal wetlands in their watershed. This research has been conducted as part of the Sustainable and Healthy Communities National Research Program. In this study, the EPA and university scientists have demonstrated that denitrification, a key process in nitrogen removal, varies among habitats across a salt marsh in the Yaquina estuary (OR) watershed, and are exploring how habitat- and spatial differences in biophysical properties of the habitats contribute to variation in denitrification.
Modeling denitrification (DeN) is particularly challenging in tidal systems, which play a vital role in buffering adjacent coastal waters from nitrogen inputs. These systems are hydrologically and biogeochemically complex, varying on fine temporal and spatial scales. As part of a modeling effort to predict spatio-temporal dynamics of DeN in salt marshes with high percent cover of nitrogen-fixing red alder in their watersheds, we assessed the spatial variability of DeN using static core incubations of surface soils of Winant salt marsh located in Yaquina Estuary, OR. During the summer of 2013 we found high marsh habitats to have significantly higher DeN rates (Wilcoxon test, p < 0.05) and higher spatial variability in DeN rates (Levin’s test, p-value < 0. 01) compared to low marsh and channel bank habitats. In the fall of 2015, we focused in on this high marsh habitat, assessing the relationship between soil extractable NO3- concentrations and DeN rates across the range of NO3- concentrations found in the marsh. In previous potential-DeN studies (2010 and 2011) nitrogen was found to be the primary nutrient limiting DeN within this marsh and across habitats within the estuary. Initial results suggest an exponential function best explains the relationship between DeN and soil extractable NO3- concentrations. Further work will be done to characterize the spatial relationships between DeN rates in the high marsh habitat and other on-site properties (e.g., elevation, plant community composition, total carbon, total nitrogen, pH, soil respiration rates).