Modeling Denitrification Across An Agricultural Catchment In A Changing Climate
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An overabundance of nitrogen (N) in marine and freshwater ecosystems has been linked to diverse, usually negative, effects on human health and the environment. One natural process that reduces N loads to downstream waters is denitrification, the microbially mediated reduction of NO3- to N2, NO, or N2O gas; however, it is difficult to quantify denitrification rates and even harder to extrapolate them spatially and t emporally to generate landscape-scale estimates of denitrification. Additionally, we expect that the changes in temperature and precipitati on projected for the end of the century may alter the rates and patterns of denitrification. We developed a coupled hydrologic-denitrification model that predicts daily denitrification rates across an agricultural watershed and was parameterized using in-situ denitrification measurements and two types of hydrologic observations (streamflow and upland soil moisture). The model fits well with the observed denitrification (R 2=0.75), stream discharge (R2=0.71) and soil moisture (R2=0.85). The modeled values did not match well with areal denitrification observations determined from isotopic analysis of the nitrate and a mixing model, and further work needs to be done to understand this discrepancy. Looking to the future, our results suggest that denitrification rates will increase, particularly in areas with high baseline rates, that the spatial and temporal patterns will not change appreciably, and that temperature increases will be the major driving factor of the projected rate changes.