Constraining carbon and sulfur dynamics in Lake Erie nearshore waters: A chemical and isotopic reconnaissance study

Past studies have documented contrasting geochemical responses of the Great Lakes to anthropogenic disturbances of the carbon and sulfur cycles. Yet, it is unclear whether these responses were induced by differences in tributary inputs or different behaviors controlled by in-lake biogeochemical processes. To yield insight into the carbon and sulfur dynamics across the land-lake interface, concentrations of chloride (Cl-), sulfate (SO42-), dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC) were measured in water samples from nearshore and offshore sites at Lake Erie, the Detroit River, and other tributaries. The stable isotope ratios of water (delta O-18 and delta H-2), sulfate (delta S-34(SO4) and delta O-18(SO4)), and the stable and radio isotope ratios of DIC (delta C-13(DIC) and Delta C-14(DIC)) were also measured. Our results confirm that waters from Lake Erie characterized by low Cl- and SO4,2- low deuterium excess (d-excess = delta H-2 - 8 delta O-18), and high delta C-13(DIC), Delta C-14(DIC), delta S-34(SO4), and delta O-18(SO4), were chemically and isotopically different from tributary waters. The nearshore waters exhibited significant correlations between various pairs of chemical and isotopic parameters revealing the influence of inputs from the tributaries. Moreover, the nearshore waters had lower averages of Cl-, SO42-, DOC, DIC, and delta O-18, but higher averages of delta C-13(DIC), Delta C-14(DIC), and delta S-34(SO4) than those estimated from binary mixing between lake and tributary waters, suggesting an effect of in-lake biogeochemical transformations. But the rates of carbon and sulfur transformations differed considerably. Thus, we suggest that the contrasting geochemical responses were induced by both their different in-lake transformation rates and their different histories of tributary inputs.