Are the benthic macroinvertebrates assimilating C and N from sewage treatment plants (STPs) in the Conodoguinet Creek watershed? Stable isotopes provide insight about pollution tolerance and opportunistic use as a basal energy and nutrient source for indicator and invasive species, and may also indicate extent of consumer exposure to emerging STP-derived contaminants recently documented in this flow system. This study measured assimilation of sewage effluent by dominant macroinvertebrates (Corbicula fluminea, Gammarus, and caddisfly larvae, Hydropsyche and Cheumatopsyche) with stable isotopes of C and N. If macroinvertebrates are assimilating energy and nutrients from the STPs, they may also be assimilating toxins such as heavy metals or endocrine disrupting chemicals, which can also be transferred up the food web, harming organisms at higher trophic levels through bioaccumulation. 

Results/Conclusions

Particulate matter values from three sewage treatment plants (STPs) along the Conodoguinet Creek in the Susquehanna watershed ranged from -23.2 to -28.6 for δ¹³C and 10.2 to 22.4 for δ¹⁵N, and were isotopically distinct from upstream macroinvertebrates. Downstream macroinvertebrate isotopic ratios were closer to those of the sewage endmembers than upstream macroinvertebrates. Particularly strong dependence on sewage effluent was noted in Hydropsychidae immediately below the upstream-most STP, where sewage derived C and N assimilation showed maximum values of 85%. Corbicula at the downstream-most site also shifted strongly toward the sewage endmembers. Since macroinvertebrates at the STPs studied are assimilating C and N from the STPs, they are a possible vector for toxins to organisms at higher trophic levels.