Carbon cycling in Lake Erie during cultural eutrophication over the last century inferred from the stable carbon isotope composition of sediments |
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Authors: | Yuehan Lu Philip A. Meyers Brian J. Eadie John A. Robbins |
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Affiliation: | (1) Department of Geological Sciences, University of Michigan, 2534 C.C. Little Bldg, 1100 N. University Ave., Ann Arbor, MI 48109, USA;(2) NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105-2945, USA;(3) Present address: Keck Environmental Laboratory, Virginia Institute of Marine Sciences, College of William and Mary, 1 Wake Drive, Williamsburg, VA 23187, USA |
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Abstract: | A ~106-cm sediment core from the eastern basin of Lake Erie was examined to investigate biogeochemical processes in this large lake during its cultural eutrophication over the last century. We measured stable carbon isotopes of total organic carbon and calcium carbonate (δ13CTOC and d13 textCtextCaCO 3 delta^{13} {text{C}}_{{{text{CaCO}}_{ 3} }} ) as well as the concentrations of total organic carbon (TOC) and calcium carbonate (CaCO3). δ13CTOC and TOC show a strong positive correlation throughout the core and record changes in phytoplankton productivity and nutrient loading. CaCO3 and TOC concentrations display a negative correlation throughout the core, suggesting that CaCO3 concentrations are controlled primarily by decomposition of TOC in the hypolimnion and the sediments, although temperature and invasive mussels are also potential controlling factors. d13 textCtextCaCO 3 delta^{13} {text{C}}_{{{text{CaCO}}_{ 3} }} values show a positive correlation with δ13CTOC between 1909 and 1969, indicating phytoplankton productivity was the primary control for d13 textCtextCaCO 3 delta^{13} {text{C}}_{{{text{CaCO}}_{ 3} }} values during eutrophication. However, a negative correlation between d13 textCtextCaCO 3 delta^{13} {text{C}}_{{{text{CaCO}}_{ 3} }} and δ13CTOC from 1970 to 2002 suggests that these two proxies tracked different aspects of the carbon cycle in the lake in more recent times. The cause for the negative correlation is not yet known, but it is perhaps associated with temperature variations and seasonal differences in productivity. |
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