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Recent changes in Lake Erie (North Shore) phytoplankton: Cumulative impacts of phosphorus loading reductions and the zebra mussel introduction

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Title: Recent changes in Lake Erie (North Shore) phytoplankton: Cumulative impacts of phosphorus loading reductions and the zebra mussel introduction
Author: Nicholls, K. H.; Hopkins, G. J.
Abstract: Analyses of phytoplankton samples collected weekly and year-round at municipal water supply intakes in Lake Erie have shown a response to long-term changes in phosphorus loading and the more recent invasion of zebra mussels. Total phytoplankton densities in the western basin of Lake Erie declined from about 5000 Areal Standard Units (A.S.U.)/mL during the late 1960s to less than 1000 A.S.U./mL by the mid-1980s and coincided with declines in total phosphorus inputs to the western basin of about 50%. Similar declines were not observed at sites in the central and eastern basins; however, a further dramatic decline (>90%) at all four Lake Erie sites during 1988-1990 coincided with the invasion of the lake by zebra mussels (Dreissena polymorpha). Similar declines in phytoplankton were not observed at reference sites in southern Lake Huron, where zebra mussels were not abundant. In the western basin, chlorophyll a concentrations of <1 ?g/L for most of the April to September period of 1991 were typical of oligotrophic areas of the upper Great Lakes. The proportional representation by the dominant classes of algae remained unchanged after the zebra mussel invasion indicating that all classes of algae were equally affected, including the large colony-forming diatoms that dominated the phytoplankton of the western basin in previous years.
URI: http://hdl.handle.net/10214/15572
Date: 1994
Rights: Queen's Printer for Ontario, Crown Copyright, Non-Commercial Use Permitted
Rights Holder: Queen's Printer for Ontario


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