Energy limitation or sensitive predators? Trophic and non-trophic impacts of wastewater pollution on stream food webs (Q6694600)

Impacts of environmental stressors on food webs are often difficult to predict because trophic levels can respond in divergent ways, and biotic interactions may dampen or amplify responses. Here we studied food-web level impacts of urban wastewater pollution, a widespread source of degradation that can alter stream food webs via top-down and bottom-up processes. We selected ten pairs of sampling locations (i.e., twenty sites total) in ten small-to-medium tributaries of the Ebro River (NE Iberian Peninsula; see "Related article" for locations). These streams were located in low-mountain habitats (365 m – 950 m a.s.l.) under the influence of Mediterranean climate and flow regimes (mean daily discharge 0.05 ± 0.09 m3·s-1). Hydrology in the region is characterized by dry summer periods with reduced flows, and rainfall episodes in spring and late fall. We surveyed the sites in early spring (April 15 - 23, 2016) to avoid spring floods; the last scouring flood preceding our sampling took place 5 months before sampling (November 2nd, 2015). Each sampling location was upstream or downstream of an urban wastewater effluent. Sewage impacts represented the main stressor influencing downstream community composition. The present dataset contains  (i) aquatic invertebrate and vertebrate community composition, and (ii) Stable Isotope Analysis data (13C/12C and 15N/14N) for each taxa and reach.