Please join the Great Lakes Center for the seminar "Sediment Geochemistry and Nutrient Dynamics in the Upper Great Lakes," presented by Sergei Katsev, professor of physics at the University of Minnesota Duluth's Large Lakes Observatory. All are welcome.
Sediments supply a significant proportion of productivity-limiting nutrients to the water columns of lakes. Despite this importance, the geochemical properties of sediments and the fluxes of nutrients and carbon in the Great Lakes are surprisingly poorly quantified. The talk will discuss past investigations in Lake Superior and ongoing efforts in Lakes Michigan and Huron. We characterize the efficiency of P recycling in sediments at multiple locations, including porewater analyses, chemical extractions for P and Fe fractions in solid phases, and sediment-water exchange fluxes of P. In the deep sediments of Lake Superior, only 12 percent of deposited P is recycled back to the water column, but effluxes of dissolved phosphorus (2.5-7.0 μmol m-2 d-1) still account for 40 percent of all P inputs into the water column. Using mass-balance modeling, we analyze the historical data for phosphorus content in the Great Lakes and predict the time scales over which they respond to changes in external loadings. In Lakes Michigan and Huron, preliminary experimental data and modeling suggest that the spread of quagga mussels has significantly modified the benthic exchanges of phosphorus, tipping the system into a new ecological regime where stronger oligotrophic conditions are projected to be achieved for the same external P loadings. The interplay of the same processes in Lake Erie, however, may lead to an opposite response.
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