GEOLOGIC AND ANTHROPOGENIC INFLUENCES ON INCREASED SEDIMENT LOAD IN SHAKOPEE CREEK: WEST-CENTRAL MINNESOTA

Shakopee Creek is one of three major tributaries to the Chippewa River in the Minnesota River Basin, West-Central Minnesota. The Chippewa drains 2080 sq miles, 320 of which are associated with Shakopee Creek. The total suspended solids (tss), and the values for erosion and turbidity in this creek, are abnormally high. This study was undertaken to determine to whether the high sediment load is due to the surficial geology or anthropogenic factors, or a combination.

I surveyed the creek looking for changes in geology noting the presence of human installments and land-use patterns. I collected and analyzed tss and tubidity data, did air photo and soil map analysis, and conducted transparency tube tests. Some water samples were taken under the auspices of the Chippewa River Watershed Project.

This creek is tiled and ditched for agricultural purposes and lacks natural areas surrounding its banks. Most marshes and wetlands have been drained. The surficial geology through which it runs starts as glacial till at its headwaters and then changes to silty clay glacial lake sediment. This geologic boundary is where the tss load drastically increases. The augmentation in suspended solids after the apparent crossing of this boundary may be due to the silty nature of the sediment, causing it to be easily suspended, especially with seasonally variable flows.

I conclude that it is both the geology and the anthropogenic features that are affecting the tss load in Shakopee Creek. The original drainage problems may be due to the existing geology, but the erosion, tss load, and turbidity have been accelerated by the land practices in the creek's drainage area. It warrants further research as this creek is posing environmental threats to the landowners and the health of it's ecosystem.

Research for this study was funded by a grant from the National Science Foundation - Research Experiences for Undergraduates (REU) Program (NSF-EAR 9820249).