We characterized stable isotope mixing along a river-Great Lake transition zone in the St. Louis River, an important fish nursery in western Lake Superior, and used it to identify food web linkages supporting young fish production. We observed a broad, spatial pattern in the carbon stable isotope ratio (δ13C); downriver enrichment in particulate organic carbon and aquatic vegetation δ13C, as well as pelagic, benthic and littoral invertebrate δ13C, reflected isotope mixing along the river-lake transition zone. Fishes with similarly enriched δ13C were used to identify benthopelagic and littoral trophic pathways. River and Lake Superior organic matter (OM) sources contributed to both pathways. Differences between the δ13C in fishes and invertebrate prey revealed that fish production was supported at multiple spatial scales. The result was that the food web specific to any location along the transition zone incorporated multiple OM sources from across the watershed.
- Lake Superior
- St. Louis River