Triska, F. J.. U.S. Geological Survey, fjtriska@usgs.gov
Jackman, A. J.. University of California at Davis, ajackman@usgs.gov
Duff, J. H.. U.S. Geological Survey, jhduff@usgs.gov
Avanzino, R. J.. U.S. Geological Survey, avanzino@usgs.gov

 
IMPACT OF BEAVER DAMS ON TRANSPORT AND TRANSFORMATION OF DISSOLVED INORGANIC NITROGEN (DIN) IN SURFACE AND PORE WATER: SHINGOBEE RIVER, MINNESOTA, USA
 
Conservative tracer injections (chloride and rhodamine WT) were used to examine DIN cycling in both surface water and pore water beneath a relict beaver dam. Rhodamine WT injected 1.2 m into sediments behind a beaver dam, and chloride injected into surface water indicated rapid subsurface transport beneath the dam (6-75 cm/h) and mixing of surface and pore water downstream from the base of the dam. The ammonium concentration at the injection well (790 ug-N/L) was higher than typical groundwater (325 ug-N/L) or surface water (25 ug-N/L), but lower than pore water in nearby sediments at 10 cm (2480 ug-N/L), 20 cm (7360 ug-N/L) and 40 cm (8440 ug-N/L) depth. Pore water concentration of nitrate in downstream hyporheic areas was often higher than groundwater or surface water where the tracers indicated surface water-pore water mixing. The results indicate possible nitrification during subsurface transport even though dissolved oxygen concentrations were low in most pore waters (<1.0 mg/L). The results indicate preservation of sub-channel hydrologic function following extended burial by beaver activity. Long-term storage of particulate organic matter with associated ammonification should shorten the turnover length of nitrogen during transport through beaver impacted reaches.
 
Day: Friday, Feb. 5
Time: 08:30 - 08:45am
Location: Sweeney Center
 
Code: CS55FR0830S