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Paleolimnological techniques were used to reconstruct past changes in lake water quality at Meridian Lake, Washington. A core was taken from the lake and dated using 210Pb and pollen analysis. Diatom microfossils showed two periods of increasing trophic status. The first came in the 1880s when the watershed was deforested, and the second occurred in the late 1940s when the watershed was developed for suburban housing. In the Meridian core, eutrophication was indicated by increasing percentages of Asterionella formosa in the fossil diatom assemblage. In 15 other western Washington lakes where core tops and bottoms were examined, Asterionella also increased with human disturbance. On the basis of previous laboratory measurements of nutrient-limited growth, Asterionella seems to be adapted to lakes with high phosphorus levels but low silica levels—characteristics of lakes which have eutrophied.
paleolimnology, diatoms, pollen, Washington, eutrophication, Asterionella formosa, sediment
Associate professor, Southern Illinois University, Edwardsville, IL