NON-UNIFORM GROUNDWATER AND NUTRIENT INPUT IN THE UPPER KALAMAZOO RIVER, MICHIGAN

The goal of this research is to document the variability of groundwater input into the Upper Kalamazoo River and potential implications for water quality. The Upper Kalamazoo River is a low-profile, gaining, meandering stream with an adjacent wetland corridor and underlying Late Wisconsinan glacial sediments. Detailed stream bed temperature maps along ~100 m reaches of the North Branch of the Kalamazoo River indicate variable groundwater input. Broad areas of the stream are above 20°C. Localized cold spots, ranging from 1.0 m² to less than a 0.2 m² in size, have temperatures as low as 10°C. Measured seepage rate in a cold area is 3.9x10^-4 cm/sec compared to 3.2x10^-6 cm/sec in a warm area. The 100 times greater seepage rate in the cold area indicates the stream is fed disproportionately by small areas of focused flow.

In addition to detailed temperature mapping, reconnaissance mapping along a 9 km reach shows numerous springs in the riverbed and along its banks. The largest measured spring has a flow rate of 6.5x10^-3 m³/sec. Many of these are expressed geomorphically as small reentrants, presumably caused by basal sapping. These reentrants are visible on high resolution Google Earth imagery but do not appear on topographic quadrangles. There does not appear to be a simple correlation between sediment type and location of springs. Cold areas show slight clustering in approximately 100 to 400 m sections but still show considerable variability in location.

This, and previous studies, show that this reach of the Kalamazoo River has nitrate levels of 2-6 ppm. In contrast, springs contain relatively high nitrate, 11-20 ppm. Many, but not all, areas with cold sediment have similarly high concentrations in pore water. Pore waters in warm sediment and surface runoff from adjacent wetlands have uniformly low, less than 1 ppm, nitrate levels. The upper portion of the aquifer is reported to be contaminated with nitrate. Where this water passes through organic-rich wetland and riverbed sediments, nitrate is reduced and removed. In areas of focused flow, the nitrate is not reduced and is carried into the stream. A simple mass balance calculation suggests that at least a quarter of the base flow in the river bypasses the reducing sediment.