Great Lakes coastal wetlands are critical intermediate habitats between terrestrial and deeper aquatic ecosystems. These wetlands perform several ecosystem services including sediment trapping, water purification, shoreline protection, flood control, and nutrient cycling. The complex hydrology, biogeochemistry, and physical morphology of these ecosystems facilitates high rates of primary productivity that sustains local consumers and can subsidize food webs in adjacent habitats. Wetland ecosystems are supported by a variety of basal energy sources, but the relative role of aquatic macrophytes and algae and their contributions to food webs remains difficult to quantify. The stable isotopes of carbon (13C) and nitrogen (15N) are often used to determine relative contributions to a food web and estimate a consumer’s trophic position, respectively. This study implements a novel isotopic tracing technique that integrates C, N, and S isotope data with mercury to estimate basal energy contributions. Representatives from multiple lower trophic levels were sampled from six wetlands within a large freshwater estuary and analyzed for isotopic ratios and mercury concentrations. Isotope mixing models will be used to distinguish among basal energy sources to the food web. This multidimensional approach allows a comprehensive analysis of lower food web structure, especially the relative energetic contributions of algae and macrophytes.