Influences of Modified Landscapes on Aquatic-Terrestrial Invertebrate Fluxes in the Scioto River, OH: Implications for Riverine Food Webs

Terrestrial and aquatic components of riverine ecosystems are inexorably linked through physical processes and exchanges of energy and materials.  Human encroachment in river floodplains and riparian areas and land conversion to urban and agricultural development is widespread, particularly along large streams and rivers.  The potential effects of anthropogenic disturbances to river hydrology, geomorphology, and water quality are relatively well-documented.  However, direct and indirect consequences of this expanding human footprint and the impacts to riverine food webs and aquatic-terrestrial linkages are not as well understood. We sampled emergent aquatic macroinvertebrates and terrestrial riparian arthropods at twelve river reaches (~1.2 km) of the Scioto River, Ohio, USA during the summer and early fall 2010-2011.  Our study reaches were characterized by three dominant landscapes: urban, row-crop agriculture, and forest.  We collected emergent insects using Mundie-style emergent traps and terrestrial arthropods entering the river channel using large floating pan traps.  All invertebrates were identified to family.  Subsequently, richness and diversity indices (H’ and 1/D) were calculated for both aquatic and terrestrial components of invertebrate fluxes.  Biomass (g m^-2) and abundance estimates (no. m^-2) of emergent and terrestrial invertebrates were also quantified. Results to-date point to a greater diversity of invertebrate families, both terrestrial and aquatic, at forested river reaches than at agricultural and urban reaches. Based on our biomass and abundance measures, we found that forested river reaches received greater abundance and biomass of terrestrial arthropods entering the stream.  Furthermore, although assemblage composition differed, abundance and biomass of emergent macroinvertebrates were comparable across reaches.  Overall, our findings indicate divergent measures of invertebrate diversity and productivity among land uses and given the important role of invertebrates in riverine food webs, we anticipate that this will have implications for higher consumers.  In particular, we expect shifts in fish assemblage composition and food web structure to reflect the changing characteristics of macroinvertebrate assemblages and the relative magnitude of terrestrial arthropod fluxes across reaches.  We also anticipate concurrent impacts to other riverine taxa, including avian consumers heavily reliant on emergent aquatic macroinvertebrates.