Primary productivity retrospection in the Great Lakes: a comparison of geochemical methods

Session: Great Lakes Primary Production: Methods, Results, and Management Implications (1)

Euan Reavie, University of Minnesota Duluth, [email protected]
Meijun Cai, Natural Resources Research Institute, University of Minnesota Duluth, [email protected]
Carsten Meyer-Jacob, Paleoecological Environmental Assessment and Research Laboratory, Department of Biology, Queen’s University, [email protected]
John Smol, Queen’s University, [email protected]
Josef Werne, Department of Geology and Environmental Science, University of Pittsburgh, [email protected]

Abstract

Several geochemical proxies are used to reconstruct long-term productivity from lake sediment records. Here we consider several proxies from the Laurentian Great Lakes: chlorophyll, organic carbon and nitrogen content, carbonates, sediment accumulation, ?¹³C, ?¹⁵N and the ratio of carbon to nitrogen. Overall, a history of cultural eutrophication is apparent in profiles of these proxies, and more recently water quality improvements and the effects of invasive mussels have been manifested as lower phytoplankton productivity. However, some proxy conflicts are apparent in some lakes, indicating that multiple environmental factors drive these proxies, and so relying on any single proxy may be a poor approach to inferring lake productivity. For instance, higher values of ?¹³C and ?¹⁵N traditionally indicate higher productivity, but in some Great Lakes cores these analytes were not correlated, and in the case of Lake Superior they were inversely related. It is clear that paleoproductivity inferences require a multi-indicator approach that can provide a weight of evidence of long-term trends.

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