Influence of terrestrial vegetation on sediment-forming processes in kettle lakes of west-central Minnesota

The composition, magnetic characteristics, and pollen content of sediments from two small kettle lakes near the prairie-forest border in west-central Minnesota were used to infer changes in terrestrial vegetation, shoreline erosion, eolian inputs, carbonate deposition, and aquatic productivity. Several important changes in sediment stratigraphy coincide closely with changes in the terrestrial pollen assemblage. Accumulation rates of organic, inorganic, and carbonate sediment fractions as well as the concentration of magnetic particulates increased abruptly as prairie replaced pine forest, and decreased gradually throughout the subsequent transitions to oak scrub, and later, mixed woodland. Results suggest that by its mediation of wind exposure, local vegetation may affect (1) influx of eolian particulates, (2) erosion of shorelines, (3) water circulation, and (4) carbonate equilibria. In addition, low rates of accumulation of organic matter and increased humidicity during periods of conifer vegetation suggest that humic matter leached from forest soils may influence lake-water chemistry and reduce productivity. Changes in lake level caused by differential rates of evapotranspiration of the various vegetation types (conifer forest, deciduous hardwood forest, brush scrub, and prairie) could not be detected. Sediment-forming processes can therefore be altered by changes in local terrestrial vegetation through several mechanisms that are independent of changes in lake level.