CS33 Sediment-Water Interactions
Date: Wednesday, June 12, 2002
Time: 4:45:00 PM
Location: Saanich
DuffJH, US Geological Survey, Menlo Park, CA, USA, jhduff@usgs.gov
Hendricks, S, P, Murray State University, Murray, KY, USA, 
Jackman, A, P, University of California, Davis, CA, USA, 
Triska, F, J, US Geological Survey, Menlo Park, CA, USA, 
The influence of Elodea canadensis on porewater chemistry, microbial respiration, and nutrient retention in the Shingobee River, MN.
Stainless steel drivepoints were used to measure vertical porewater solute gradients in two distinct streambed environments - streambed with actively growing Elodea beds and streambed lacking rooted aquatic macrophytes. Drivepoint clusters were placed at the upstream, middle, and downstream areas of the beds. Piezometric head measurements indicated the Elodea beds were located in zones of diffuse groundwater discharge. Groundwater was relatively high in DIC and ammonium compared with the channel, which may help rooted macrophytes become established following snowmelt. The upstream end of the Elodea beds had the highest accumulation of nutrients. As the communities matured, porewater became chemically reduced and nutrient levels increased one to two orders of magnitude above background in the root-zone. These levels were significantly higher than those found in either groundwater or surface water indicating the beds served as a nutrient reservoir. Sediment respiration, nitrification and denitrification in Elodea beds were all higher than control sediments, indicating Elodea beds were zones of high metabolism. Finally, surface water nitrate was unaffected by Elodea plants during daytime suggesting porewater ammonium was an important nitrogen source for Elodea production.