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
Assistance with the push-pull method was provided by T. Anderson, assistance in the field and laboratory was provided by L. Kreitinger, A. Fortman, and S. Giri, and site access was provided by S. McKay. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1144153 and the Cornell Cross-Scale Biogeochemistry & Climate IGERT under NSF Grant No. 1069193. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
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