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Modeling the Effects of Climate Change on Spatio-Temporal Dynamics of Denitrification in an Oregon Salt Marsh
Citation:
Moon, J., K. Naithani, J. Stecher, Ted DeWitt, A. Nahlik, M. Fennessy, AND R. Regutti. Modeling the Effects of Climate Change on Spatio-Temporal Dynamics of Denitrification in an Oregon Salt Marsh. Society of Wetland Scientists Annual Meeting, Corpus Christi, TX, May 31 - June 04, 2016.
Impact/Purpose:
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 demonstrate an ecological model they have constructed to estimate how climate change could affect denitrification rate, a key process in nitrogen removal, based on data collected from a salt marsh in Yaquina estuary (OR). The model predicts that as sea level rises and inundates marsh habitats more frequently, denitrification rates should increase which could lead to an increased capacity of salt marshes to remove reactive nitrogen from surface waters and ground water. However, climate change may also cause changes to the abundance of nitrogen-fixing red alders in upslope forests or change the spatial configuration of marsh habitats, both of which could affect the magnitude of denitrification in salt marshes which will be investigated next.
Description:
The highest uncertainties in net nitrogen (N) fluxes between the atmosphere and biologically active pools are predominately due to denitrification (DeN). This diminishes confidence in our assessment of wetland N removal at transition zones between upland and aquatic systems. This is relevant given the exponential spread of dead zones in coastal oceans since the 1960s and expected future shifts in climate. Salt marshes are highly susceptible to a range of climate change effects (e.g., sea-level rise, salinity change, vegetation change, storm severity), all of which may affect the spatial and temporal dynamics of DeN. To address this, we have built a probabilistic model of DeN in a salt marsh on the Oregon coast. Salt marshes in this region will be impacted by sea level rise and upslope shifts in red alder, a N-fixing plant. Our model accounts for spatial variability in soil nitrate and oxygen availability as a function of landscape position metrics (e.g., elevation, distance to channel, and upslope red alder). Initial simulations suggest that as sea-level rises, DeN will increase non-linearly; “hot spots” near the marsh-upland toe-of-slope will become more active as inundation periods lengthen. However, the model also revealed that only a small fraction of the dissolved N coming into the watershed from N-fixing red alder is denitrified in the marsh during inundation periods. With optimal soil moisture conditions for DeN maintained during non-inundating neap tides, the next step is to include those periods in the model. We will also include terms to account for soil accretion, changes in NO3- loading dynamics due to changes in the distribution of upslope red alder, and marsh-area loss to open water habitat.