Siliceous microfossil succession in the recent history of Green Bay,Lake Michigan |
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| Authors: | E F Stoermer J P Kociolek C L Schelske N A Andresen |
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| Institution: | (1) Center for Great Lakes & Aquatic Sciences, University of Michigan, 48109 Ann Arbor, MI, USA;(2) Department of Invertebrate Zoology & Geology, California Academy of Sciences, Golden Gate Park, 94118 San Francisco, CA, USA;(3) Department of Fisheries and Aquaculture, University of Florida, 7922 NW 71st Street, 32606 Gainesville, FL, USA |
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| Abstract: | Quantitative analysis of siliceous microfossils in a 210Pb dated core from Green Bay of Lake Michigan shows clear evidence of eutrophication, but a different pattern of population succession than observed in the main deposition basins of the Great Lakes. Sediments deposited prior to extensive European settlement (ca A.D. 1850) contain high relative abundance of chrysophyte cysts and benthic diatoms. Quantity and composition of microfossils deposited during the pre-settlement period represented in our core is quite uniform, except for the 30–32 cm interval which contains elevated microfossil abundance and particularly high levels of attached benthic species. Total microfossil abundance and the proportion of planktonic diatoms begins to increase ca 1860 and rises very rapidly beginning ca 1915. Maximum abundance occurs in sediments deposited during the 1970's, with a secondary peak in the late 1940's — early 1950's. Increased total abundance is accompanied by increased dominance of taxa tolerant of eutrophic conditions, however indigenous oligotrophic taxa, particularly those which are most abundant during the summer, are not eliminated from the flora, as in the lower Great Lakes. It appears that a combination of silica resupply from high riverine loadings and replacement of indigenous populations by periodic intrusions of Lake Michigan water allow sequential co-existence of species usually exclusively associated with either eutrophic or oligotrophic conditions. |
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| Keywords: | diatoms paleolimnology eutrophication Great Lakes Green Bay Lake Michigan North America |
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