| Virginia
Journal of Science.
2001. Vol 52 (4) : 241-258 |
| An
Examination of the First Sediment Cores from Mountain Lake, Giles
County, Virginia, for Diatoms and Pollen. Jon C. Cawley, Biology Department, Roanoke College, Salem, VA 24153, Bruce C. Parker, Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A. and Terry L. Hufford, Department of Biological Sciences, The George Washington University, Washington, DC 20052, U.S.A. ABSTRACT
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.Key words: Mountain Lake, paleolimnology, diatoms, sedimentology, water fluctuation, solar minima. |