Large rivers are important for economies and global ecosystems. The importance of large rivers to societies is easily recognizable because many modern and ancient population centers are located along large rivers, tributaries, streams, and deltas. Although engineering in river systems has economic benefits to society, these benefits often come with devastating ecological consequences that, if not fully considered, may eventually counterbalance the economic benefits.
Understanding energy flow, nutrient cycling pathways, and relative importance of terrestrial and aquatic carbon sources supporting aquatic consumers in large river food webs is essential in planning for wildlife conservation, environmental protection, and floodplain management. Scientists debate which factors control the relative importance of organic sources fueling food webs of large rivers. Resolution of this debate requires a new technique: identifying food sources using traditional bulk-tissue stable isotope techniques is difficult because of spatiotemporal variability of carbon sources, mixing model problems with too few tracers, and unavailability of reliable basal signatures. In this project, we utilize a new technique, applying nitrogen and carbon stable isotope analysis of essential amino acids (δ15NEAA, δ13CEAA) to museum fish specimens, to determine trophic position and carbon food sources over time and possible shifts in response to river engineering in the Mississippi and Ohio rivers.