PARENT SESSION
Oral Session 1: Aquatic Ecology I: Rivers, Nutrients, and Water Quality.
Presiding: D Kashian
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 105.
Changes in denitrification following reintroduction of flooding to a leveed Midwestern floodplain.
Orr, Cailin*,1, Stanley, Emily1, Wilson, Karen2, Finlay, Jacques3, 1 Center for Limnology, Madison, WI, USA2 University of Toronto, Toronto, ON, Canada3 University of Minnesota, St. Paul, MN, USA
ABSTRACT- River floodplains have the potential to mediate anthropogenic nitrate loading to riverine water through denitrification, the anerobic microbial conversion of nitrate to nitrogen gas. An important factor in this process is the interaction of river water with floodplain soil, however many rivers have been disconnected from their historic floodplains by levees. To test the impact that restoring flooding to a degraded floodplain has on floodplain soil denitrification rates, we studied change in denitrification rates on the Baraboo River, Wisconsin floodplain before and after a restoration project that restored a degree of connectivity between the river and the floodplain. Prior to this manipulation the site had been leveed, drained, and farmed for more than 50 years. In 2002 the field drainage system was removed and a gate structure was installed to allow controlled inundation during periods of high flow. We measured denitrification in static cores and potential denitrification in carbon and nitrate amended samples for two years before and after the manipulation. Denitrification rates showed high temporal and spatial variability consistent with other studies of floodplain denitrification. Denitrification increased in amended samples from before flooding 0.045 
N2O-N kg-1soil hr-1 (SD = 0.089) to after flooding 2.59N2O-N kg-1soil hr-1 (SD = 2.54) and the average rates were significantly different between years (p<0.001). Even though denitrification rates increased, total nitrogen in the soil did not change from 2002 to 2003 (0.31% to 0.33%, p<0.27). These results demonstrate that with the continuation of management for flooding, floodplain denitrification could potentially remove significant amounts of N derived from riverine water and that floodplain restoration in general may be a good method for dealing with excess riverine nitrogen.
Key words: denitrification, floodplain, restoration