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Denitrification in Alluvial Wetlands in an Urban Landscape
Citation:
Harrison, M. D., P. M. Groffman, P. M. MAYER, S. S. Kaushal, AND T. A. Newcomer. Denitrification in Alluvial Wetlands in an Urban Landscape. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 40(2):634-646, (2011).
Impact/Purpose:
The purpose is to conduct studies to verify if urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds.
Description:
Riparian wetlands have been shown to be particularly effective “sinks” for nitrate-N (NO3-), minimizing the downstream export of nitrogen (N) to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We investigated the variation and magnitude of denitrification in three constructed and two relict oxbow urban wetlands and in two forested reference wetlands in the Baltimore metropolitan area. Denitrification rates in wetland sediments were measured with an 15N-enriched NO3- “push–pull” ground water tracer method during the summer and winter of 2008. Mean denitrification rates did not differ among the wetland types and ranged from 147 + 29 μg N kg soil-1 d-1 in constructed storm water wetlands to 100 + 11 μg N kg soil-1 d-1 in relict oxbows to 106 + 32 μg N kg soil-1 d-1 in forested reference wetlands. High denitrification rates were observed in both summer and winter, suggesting that these wetlands are sinks for NO3- year round. Comparison of in situ denitrification rates with NO3- standing stocks in the wetland water column and stream NO3- loads indicated that mass removal of NO3- in urban wetland sediments by denitrification could be substantial. Our results suggest that urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds.
