QUANTITATIVE ANALYSIS OF SILICEOUS MICROFOSSILS IN THE SEDIMENTS OF LAKE ERIE'S CENTRAL BASIN

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Abstract
Quantitative analysis of siliceous microfossils preserved in a radiometrically dated core from the central basin of Lake Erie (North America) shows several distinct periods in the lake's response to anthropogenic effects. Prior to European settlement of the region, microfossil deposition rates were low, and the flora consisted mainly of oligo-stenothermal and benthic species. Deposition rates increased rapidly following settlement and the proportion of summer-blooming species, particularly members of the genus Cyclotetta, increased. During the period ca. 1920–1930 the flora underwent transition from dominance of oligo-mesotrophic species to dominance of species associated with eutrophic conditions. After ca. 1945 the flora became dominated by species tolerant of hypereutrophic conditions. The most recently deposited sediments (post- ca. 1980) contain a qualitatively different flora, probably reflecting reduction of phosphorus loadings to Lake Erie.