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Full-Text Articles in Physical Sciences and Mathematics
Origin And Developmental History Of Minnesota Lakes, H. E. Wright Jr.
Origin And Developmental History Of Minnesota Lakes, H. E. Wright Jr.
Journal of the Minnesota Academy of Science
ABSTRACT-Most lakes in Minnesota owe their origin directly or indirectly to glacial deposition or erosion 10,000 to 20,000 years ago. The lakes' shapes have since been modified by waves and currents near the shores and by the deposition of sediment off-shore-principally the sediment produced by growth of algae and other organisms. This sediment is a receptacle for pollen grains blown into the lake from the surrounding vegetation, and the stratigraphic succession of pollen grains records the postglacial vegetational and thus climatic history of the area. The sediment also preserves the fossils of microorganisms that reveal by their chemical composition the …
Susceptibility Of Northern Minnesota Lakes To Acid Deposition Impacts, Clifford J. Twaroski, J. David Thornton, Rick L. Strassman, Patrick L. Brezonik
Susceptibility Of Northern Minnesota Lakes To Acid Deposition Impacts, Clifford J. Twaroski, J. David Thornton, Rick L. Strassman, Patrick L. Brezonik
Journal of the Minnesota Academy of Science
ABSTRACT-lake chemistry surveys indicate a large number of lakes with acid neutralizing capability (ANC) below 200 μeq/L occur in northeast Minnesota where shallow soils over bedrock and exposed rock outcrops predominate, and in moraine areas having rolling to steep topography in north-central and east-central Minnesota. In the Boundary Waters area, lake chemistry is strongly associated with bedrock geology. lakes with ANC <100 μeq/L are associated with granite, basalt, and gabbro formations, while lakes with ANC of 100- 200 μeq/L are associated with slate and greenstone formations. In the rest of the state where soils are deep, landform, soil type, and lake hydrology determine lake chemistry. Most low ANC lakes are found in terminal moraine areas. These lakes are generally small ( <40 ha in area), have limited groundwater inflow, and typically classed as precipitation-dominated seepage lakes. Higher ANC lakes (>400 μeq/L) are often associated with agricultural and residential land uses. Relationships found between ANC and bedrock geology, and between ANC and landform and soils, provided the basis for mapping the distribution of low ANC surface waters in Minnesota. …