Basin sediment was studied from 20 ice-block lakes associated with nutrient-rich, intensively cultivated soils on landscapes with poorly integrated drainage in southern Minnesota. This sediment is placed in the coprogenous earth class of limnic materials. Rice and Hall Lakes were investigated in detail because of the contrast in size and relief of their watersheds. Bulk density, mineral content, and total phosphorus and potassium were measured in cores taken from the lakes.
A core from Rice Lake was sampled at selected depths for radiocarbon dating, examination of minerals, and pollen and diatom content with a petrographic microscope and X-ray analysis of the 2-to 20-micron size particles. Bulk density of the sediments increased from 0.07 g/cm3 in the layers part to 0.36 g/cm3 in the lower. Between 5.4 and 14.5 m, the bulk density fluctuated between 0.25 g/cm3 and 0.30 g/cm3. In Rice Lake, a peaty layer near 4.45 m had a much lower bulk density. Content of phosphorus and potassium increased to a depth of 10m, then decreased slightly with depth to the basin floor. Petrographic microscopic examination and X-ray analysis of the sediment identified only quartz and calcite in appreciable amounts. Crystalline silicates in the sediment are like those in nearby upland soils formed in the calcareous gray glacial drift. Diatomaceous forms and opalized plant remains were abundant.
Radiocarbon date and pollen dominance were determined at depths of 4 to 5 m and 14.5 m. The layer at 14.5 m was dated at 9675 ± 144 years before present (B.P.) and spruce pollen was dominant. The peaty layer at 4 to 5 m was dated at 1835 ± 80 B.P.
Sediment from Hall Lake had a higher bulk density, more total phosphorus, and more total potassium and mineral material than sediment from Rice Lake. These higher values probably reflect the larger amounts of upland sediment from the larger watershed and the shorter distance from the sample site to an incoming stream. Nevertheless, upland mineral types were present only in trace amounts and in sizes commonly transported by wind. Also, soil surveys located most sediment eroded from hill slopes at the foot slope. We conclude that most of the sediment was generated in the lakes themselves from dissolved nutrients.
Cummins, J.F.; Paulson, R.O.; Rust, R.H.; Gruenhagen, S.E..
Sediment in the Ice-Block Lakes in Intensively Cultivated Watersheds of Southern Minnesota.
Minnesota Agricultural Experiment Station.
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