Abstract:
Floodplain lakes are considered biodiversity hotspots within large river systems. The relative importance of allochthonous vs autochthonous carbon to the food webs of river systems has been widely debated for decades. In this study, we employed amino acid compound-specific isotope analysis (AA-CSIA) of carbon sources in fishes to determine the ultimate sources of carbon supporting the food webs in floodplain lakes of the lower Wabash River. Samples from fishes representing planktivores, piscivores, and invertivores, as well as sources of carbon (primary producers) were analyzed using AA-CSIA of carbon. Principle components analysis and linear discriminate analysis were used to identify and determine food source groups based on δ13C values. Five food source groups were identified: algae, cyanobacteria, aquatic C3 plants, terrestrial C3 plants, and terrestrial C4 plants. The MixSIAR package in R was used to estimate the relative contribution of dietary carbon from source groups to consumers. The diets of the three trophic feeding guilds primarily contained carbon from algae. The diet of planktivores did not have meaningful contributions of carbon from any other source groups. Cyanobacteria and terrestrial C4 plants were secondary contributors of carbon to the diets of piscivores and
invertivores. Our results indicate that sources of carbon for the food webs of floodplain lakes on
the lower Wabash River are autochthonous, and primarily algae.
