PATHWAYS OF NITRATE INTO THE KALAMAZOO RIVER: A PHYSICAL, CHEMICAL AND MICROBIOLOGICAL STUDY
The goal of this study was to determine the cause of this variability though examination of pore-water and sediment at several sites of diffuse flow at high rates. Pore-water was extracted at 10 cm intervals with a narrow gauge stainless steel tube. Cores of the loose sediment were collected by freezing the sediment within a PVC coring tube with an ethanol-dry ice mix in a narrow copper tube inserted into the PVC tube. Water chemistry of pore water extracted from the sediment cores was in good agreement with pore- water sampled in situ. All investigated locations of diffuse flow at high rates with high nitrate concentrations were shown to have sand or sand and gravel layers at depths of 20-30 cm, and nitrate concentrations peak at that horizon. Nitrate-metabolizing bacterial populations were also quantified using fluorescent in situ hybridization, however, no correlation can yet be made between the size of these bacterial communities and the corresponding pore-water nitrate levels. We conclude that the permeable layers of sand and gravel are the conduit for nitrate transport from adjacent upland agricultural land, through the surrounding wetland and to the river. Overpressure in these sand layers may lead in some cases to the sand boils and springs.