Mountain Lake, Virginia is a small, unique, oligotrophic, subalpine ecosystem in the southern Appalachians. Its geology, origin, climate, and history have influenced its morphometry, and therefore its sedimentology and algal flora. Radiocarbon dates establish specific Mountain Lake sediment ages at 1800, 4100, and 6100 years BP. Sediment core analysis suggests at least 6 prolonged periods when Mountain Lake probably was nearly dry or very small in size. These individual low-water periods (at approximately 100, 400, 900, 1200, 1800 and 4100 years BP) are evidenced by changes in diatom and pollen content, sedimentary erosion features, and the presence of wood fragments, plant fibers, and abundant Sphagnum and fern spores. The ratio of planktonic-to-benthic diatom taxa was used to estimate approximate past water depths from sediment. One or more of these low-water intervals may correspond to a drier climate coincident with solar activity minima. Resolution of prolonged low water intervals probably has been enhanced by the continuous loss of water through the crevice or fault at the lake bottom. The sediment core record suggests also that some eutrophication has occurred during the 20th century, in parallel with anthropogenic impacts (i.e. increased sedimentation, induced eutrophication, and diatom diversity changes). These findings provide the first published diatom, pollen and sedimentology-based paleolimnology for this lake.

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