Re-eutrophication and harmful algal blooms in Lake Erie have resulted in a renewed call for remedial measures such as reductions of phosphorus loads to the lake's western basin. The action of further nutrient reductions may also reduce the intensity of seasonal central basin hypolimnetic anoxia by reducing algal biomass. However, winter-spring blooms of diatoms have not been fully recognized as a source of algal biomass that might contribute significantly to summer hypoxia. We compared spring and summer phytoplankton abundance in central and western Lake Erie based on monitoring data to show that spring phytoplankton biovolume was 1.5- to 6-fold greater than summer biovolume and that most spring biovolume was composed of filamentous diatoms, primarily Aulacoseira islandica, that is likely supported by an increasing silica load from Lake Huron. The rise of silica export was attributed to the dreissenid mussel invasion and establishment that reduced diatom abundance in Lake Huron and thereby increased silica availability in the receiving water body of Lake Erie. The relationship between phosphorus and winter-spring diatom blooms was unclear, but diatoms probably contributed the majority of the algal biomass that accumulated annually in the hypolimnion of the central basin of Lake Erie. Remedial measures aimed at reducing hypoxia must consider the winter-spring phytoplankton bloom in Lake Erie as an important and reoccurring feature of the lake that delivers a considerable quantity of algal biomass to the profundal zone of the lake.
Bibliographical noteFunding Information:
This research was supported by a grant to E. Reavie from the U.S. Environmental Protection Agency under Cooperative Agreement GL-00E23101-2 , and a grant to M. Twiss from the New York Sea Grant Institution ( R-CE-29 ). Ship time provided by the USEPA Great Lakes National Program Office for Spring 2010 and from Environment Canada onboard the CCGS Griffon for winter sampling is gratefully acknowledged. This document has not been subjected to the EPA's required peer and policy review and therefore does not necessarily reflect the view of the Agency, and no official endorsement should be inferred. Sediment core collection was performed by Bob Sterner and the crew of the R/V Blue Heron (Large Lakes Observatory). Personnel from the Large Lakes Observatory also performed the sediment nutrient analyses. Michael Agbeti, Lisa Estepp and Elaine Ruzycki supported algal assessments of the GLNPO phytoplankton samples. Kitty Kennedy, Amy Kireta, Lisa Estepp and the crew of the R/V Lake Guardian supported phytoplankton sample collection. This is contribution number 600 of the Natural Resources Research Institute, University of Minnesota Duluth. This manuscript is GLERL contribution number 1808. The paper is contribution number 68 of the Institute for Great Lakes (IGLR) at Central Michigan University.
© 2016 International Association for Great Lakes Research.
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