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URBAN STREAM BURIAL INCREASES WATERSHED-SCALE NITRATE EXPORT
Citation:
Beaulieu, J., H. Golden, Chris Knightes, P. Mayer, S. Kaushal, M. Pennino, C. Arango, A. Balz, C. Elonen, K. Fritz, AND B. Hill. URBAN STREAM BURIAL INCREASES WATERSHED-SCALE NITRATE EXPORT. PLOS ONE . Public Library of Science, San Francisco, CA, 10(7):e0132256, (2015).
Impact/Purpose:
To inform the public
Description:
Nitrogen (N) uptake in streams is an important ecosystem service that may be affected by the widespread burial of streams in stormwater pipes in urban watersheds. We predicted that stream burial reduces the capacity of streams to remove nitrate (NO3-) from the water column by inhibiting biological NO3- demand and enhancing hydrologic NO3- export. We tested these predictions by measuring whole-stream NO3- removal rates using 15NO3- isotope tracer releases in paired buried and open reaches in Cincinnati, Ohio (USA) and Baltimore, Maryland (USA) during four seasons and using simulation modeling at the broader stream network scale. Burial reduced biological NO3- demand in all streams, as indicated by NO3- uptake velocities that were 13-fold lower than that of the open reaches. The effect of burial on hydrologic NO3- export was related to channel shape, with hydrologic export increasing with decreasing pipe width, suggesting that NO3- retention in buried reaches could be partially managed through pipe design. We used simulation modeling to scale our measurements to the 171 km2 Gwynns Falls Watershed in the Chesapeake Bay basin, and found that NO3- export increases exponentially with burial, with export increasing by 7-fold at 100% burial. This suggests that stream burial can greatly impair watershed-scale NO3- retention. Stream restoration practices involving "daylighting" buried streams have the potential to increase N retention.
