HR: 10:30h
AN: NB22E-01    [Abstracts]
TI: The Influence of Sandbar Vegetation on Hyporheic Nitrogen Processing
AU: * Predick, K
EM: kipredick@wisc.edu
AF: Center for Limnology, University of Wisconsin-Madison, 680 N. Park St., Madison, WI 53706 United States
AU: Rogers, K
EM: kristyrogers@wisc.edu
AF: Center for Limnology, University of Wisconsin-Madison, 680 N. Park St., Madison, WI 53706 United States
AU: Stanley, E
EM: ehstanley@wisc.edu
AF: Center for Limnology, University of Wisconsin-Madison, 680 N. Park St., Madison, WI 53706 United States
AB: High nitrate concentrations due to agricultural runoff are common in Midwestern rivers. While floodplains can facilitate nitrate removal through denitrification, only a small proportion of riverine flow reaches floodplains. Conditions required for denitrification also occur within in-channel sandbars, which contact river flow year round. In this study, we addressed the role of vegetated and unvegetated sandbars in nitrogen processing. Sixteen sandbars (half with vegetation, half without) were sampled along the southern Wisconsin River in July, August and September of 2004. On each sandbar, wells were installed to the water table at 5 m intervals along the length of each bar. Water samples from each well were filtered and analyzed for nitrate and ammonium. Nitrate declined significantly below riverine concentrations in all vegetated sandbars but was variable in unvegetated bars. Ammonium concentrations were significantly higher than riverine concentrations in all sandbars, with no significant difference due to vegetation. The presence of sandbar vegetation facilitated nitrate loss, potentially fueling denitrification through carbon subsidies. Nitrate declines coupled with increased ammonium concentrations suggest that dissimilatory nitrate reduction to ammonia (DNRA) was also an active process in sandbars. Therefore, vegetation stimulated nitrate decline in riverine sandbars, likely due to a combination of denitrification and DNRA.
DE: 1806 Chemistry of fresh water
DE: 9901 NABS Student Award - Basic Research
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly