Freshwater mussels are essential ecosystem engineers linking pelagic and benthic zones in aquatic systems.  As filter feeders, native mussels help purify the water and are sensitive indicators of stream health.  However, little is known about their feeding ecology.  Additionally, Corbicula fluminea, an introduced bivalve, has been associated with native mussel declines, possibly due to competition with native mussels for food resources.  Our research was designed to understand how food quality and stable isotopic composition of particulate organic matter (seston) is affected by abiotic factors.  Seston is available in the water column to filter feeders but varies in quantity and quality seasonally and interannually.  To determine dietary composition and potential overlap of Corbicula and the native mussel Elliptio crassidens, we measured the elemental and isotopic compositions of their tissue, as well as several size classes of seston at different streamflows.  Our results indicate that differences exist in the food resources utilized by the two species.  Also, the presence of Corbicula may alter nutrient cycling in the benthic environment of coastal plain streams by retaining less nitrogen than native mussels, which may modify nutrient cycling in streams.  These results have implications on how invasive species, such as Corbicula, may alter stream ecosystems.