ibclogo XVI International Botanical Congess


Abstract Number: 5044
Poster No. = 1414


TROPHIC STATE OF MOUNTAIN LAKE, GILES COUNTY, VIRGINIA


Jon C. Cawley*, Bruce C. Parker*, and Myron H. Beaty^, *Biology Dept., Virginia Tech, Blacksburg, VA 24061, ^ Biology Dept., Merrimack College, North Andover, MA 01845 USA


In 1997 and 1998, spring to fall, we measured orthophosphate, phytoplankton densities, and other variables in this natural subalpine lake, which Beaty and Parker (1994) found to be manifesting early stages of eutrophication. Orthophosphate-P levels averaging 1.5µg/L (1997) and 2.2µg/L (1998) had dropped from 27µg/L (1990). Ammonium-N also had dropped, but nitrate-N had increased in 1997-98 compared to 1990. The N:P ratio of 143:1 (1997) and 244:1 (1998) compared to 9.4:1 (1990) clearly indicating P as the major limiting nutrient. Similar phytoplankton taxa and cell densities as for 1980s-90s along with extensive other data suggest that Mountain Lake remains oligotrophic and shows no signs of eutrophication. Streams and springs feeding the lake also are low in key nutrients, but precipitation constitutes a major source of P, N, and acidity to Mountain Lake.


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