The nitrate sink function of riparian zones is dependent upon the interaction of the groundwater and the biologically active soil zone. Increased impervious surface and engineering controls (i.e. curbs, storm drainage networks) in urban areas lead to less groundwater infiltration and more runoff. This lowers water tables and reduces the opportunity for interaction between the groundwater and the biologically active soil zone. Our current study is examining hydrologic and soil disturbances that affect the denitrification capacity of riparian zones. We examined in situ groundwater denitrification (using a 15N nitrate push-pull method) within 3 meters of the stream at both shallow (50-90cm) and deep (150-200cm) depths in 6 riparian zones (3 in urban watersheds and 3 in agricultural watersheds). Preliminary results suggest that buried organic layers at depth lead to higher denitrification rates. All depths and riparian zones that did not have buried layers at depth had very little denitrification. This study will contribute to the understanding of land use change on the riparian nitrate sink function, and contribute to discussions of preservation and restoration of riparian zones in urbanizing watersheds.
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