Multiple urban stressors drive fish-based ecological networks in streams of Columbus, Ohio, USA

Integrating a network perspective into multiple-stressor research can reveal indirect stressor effects and simultaneously estimate both taxonomic and functional community characteristics, thus representing a novel approach to stressor paradigms in rivers. Using six years of data from twelve streams of Columbus, Ohio, USA, the effects of nutrients (N:P), impervious surface (%IS), and sedimentation on network properties were quantified. Variability in the strength and distribution of trophic interactions was assessed by incorporating biomass into networks. All stressors impacted some properties of network topology - linkage density (average number of links per species), connectance (fraction of all possible links realized in a network), and compartmentalization (degree to which networks contain discrete sub-webs), including synergistic interactive effects between sedimentation and stream size. We also found support for antagonistic effects between (1) sedimentation and %IS and between %IS and N:P on the weighted index mean link weight, which represents the magnitude of trophic interactions among species in a network, and (2) %IS and stream size on strength standard deviation, a measure of the distribution of total magnitude of all trophic interactions per species in a network. Overall, our results point to the potential for urban stressors such as impervious surfaces and sedimentation - alone and as interactions - to decrease network complexity, compartmentalization, and stability, likely through homogenizing habitat and limiting food resources. The observation that larger streams often buffered the negative effects of these stressors suggests that restoration and other management approaches might be most beneficial in smaller headwater streams of urban catchments.