Shifts in reciprocal river-riparian arthropod fluxes along an urban-rural landscape gradient

We measured bidirectional arthropod fluxes at 12 river reaches distributed across an urban-rural gradient of riparian land use and land cover in the Scioto River system of Ohio (U.S.A.). For the terrestrial-to-aquatic arthropod flux (i.e. inputs of terrestrial arthropods to the river from the land), urban development was positively related to density of inputs but negatively related to biomass, partially explained by shifts in community composition and body size. Riparian grassland, typical of rural (i.e. non-urban) landscapes, was positively associated with both density (range: 2.8-18.9 individuals m^-2 day^-1) and biomass (range: 7.1-58.7 mg m^-2 day^-1) of inputs. For the aquatic-to-terrestrial flux of adult aquatic insects (i.e. emergent aquatic insects exported from the river), riparian grassland cover was positively associated with both density (R² = 0.61; range: 12.8-116.8 individuals m^-2 day^-1) and biomass (R² = 0.65; range: 1.4-27.9 mg m^-2 day^-1), with relatively larger-bodied taxa dominating emergence at rural reaches. Riparian landscape composition relates to reciprocal fluxes of arthropods (aquatic insects out, terrestrial insects and other arthropods in) in river-riparian systems as we found human landscape disturbances were associated with changes in the taxonomic composition of both aquatic emergence and terrestrial input, and an overall decrease in the magnitude of emergence and terrestrial input. Furthermore, landscape changes that alter arthropod fluxes may have broader consequences for linked river-riparian biodiversity and food webs and should be taken into account in conservation, restoration and management of these systems.