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Nitrogen Uptake and Denitrification in Restored and Unrestored Streams in Urban Maryland, USA
Citation:
Klocker, C. A., S. S. Kaushal, P. M. Groffman, P. M. MAYER, AND R. P. Morgan. Nitrogen Uptake and Denitrification in Restored and Unrestored Streams in Urban Maryland, USA. AQUATIC SCIENCES. Birkhaeuser Verlag AG, Basel, Switzerland, 71(4):411-424, (2009).
Impact/Purpose:
To better understand the effects of restoration on nitrogen processing in rates of nitrate uptake and denitrification in restroed streams.
Description:
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in 2 restored and 2 unrestored streams in Baltimore, Maryland, U.S.A. using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to its floodplain. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was low in the restored streams during summer baseflow conditions. Uptake length of NO3-- N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3-- N m-2 d-1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may be a key factor in influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary, however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in response to the “flashy” hydrologic flow conditions during storms common in urban streams.
URLs/Downloads:
NITROGEN UPTAKE AND DENITRIFICATION IN RESTORED AND UNRESTORED STREAMS IN URBAN MARYLAND, USA