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GEOMORPHIC CONTROLS ON C AND N PROCESSING IN A RESTORED URBAN STREAM; POWER POINT PRESENTATION
Citation:
MAYER, P. M. AND E. J. DOHENY. GEOMORPHIC CONTROLS ON C AND N PROCESSING IN A RESTORED URBAN STREAM; POWER POINT PRESENTATION. Presented at Chesapeake Bay Program STAC Responsive Workshop at the US Fish and Wildlife Service Patuxent Conference Center, Laurel, MD, November 14, 2006.
Impact/Purpose:
To inform the public.
Description:
Stream channel incision due to hydraulic alteration stemming from urbanization may cause a disconnection between the stream channel and the adjacent floodplain. This disconnection may inhibit removal of nitrate via denitrification and/or stimulate nitrate production through nitrification in the hyporheic zone, subsequently leading to eutrophication. We examined the effects of geomorphic restoration (e.g. bank re-shaping, bank reinforcement, channel meanders, energy dissipation structures) on dissolved organic carbon and nitrate dynamics in Minebank Run, an urban stream in the Chesapeake Bay watershed, Maryland, USA. Nitrate was inversely related to dissolved organic carbon in ground water, suggesting control of denitrification by carbon availability to microbial denitrifiers. Nitrate concentration was positively related to dissolved oxygen in ground water, suggesting that lower base flow and increased hydraulic residence times promoted conditions (e.g. lower dissolved oxygen, higher water temperatures during summer, prolonged mixing with dissolved organic carbon) supporting denitrification. Measured rates of denitrification potential were higher in sediments with greater amounts of organic carbon suggesting that denitrification was an important mechanism of nitrate removal directly related to carbon availability. Nitrate was lower in restored reaches of the stream in which incised banks had been reconstructed, suggesting that geomorphic stream restoration that reconnects flood plains to stream channels may have the potential to promote removal of nitrate in ground water and, thereby, improve stream water quality. However, seasonal trends indicate that winter will be a time of elevated nitrate runoff.