Hydrologic and Biogeochemical Drivers of Riparian Denitrification in an Agricultural Watershed
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This study investigated drivers of denitrification and overall NO3− removal in an agricultural riparian area in central New York. Denitrification was measured using an in situ “push-pull” method with 15N–NO3− as a tracer during summer and fall 2011 at a pair of riparian sites characterized by different hydrologic regimes. Median denitrification rates were 1347 and 703 μg N kg soil−1 day−1 for the two study sites. These rates are higher than those reported for other riparian areas, emphasizing the role of some riparian areas as hotspots of NO3− removal. N2O production was significantly higher at one site, demonstrating that riparian areas can be a greenhouse gas source under certain conditions. Denitrification was negatively correlated with groundwater flux, suggesting that slower flushing of water, and thus longer residence time, promotes denitrification. A mass balance of NO3− loss revealed that denitrification only accounted for 5–12 % of total NO3− loss, and production of NH4+ indicated that dissimilatory NO3− reduction to NH4+ (DNRA) may be occurring at both sites. While both sites were characterized by high NO3− removal, differences in denitrification rates and NO3− removal processes demonstrate the need to improve our ability to capture spatial and process heterogeneity in landscape biogeochemical models.
KeywordsDenitrification DNRA Water quality Nitrogen cycling Riparian systems Ecohydrology Riparian groundwater
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