Urban river ecosystems are under the influence of treated wastewater effluent, but the relationship between the effluent and aquatic food web has not been well understood. In the Tama River, we investigated the effects of treated wastewater on a benthic macroinvertebrate community and main food sources for aquatic organisms including periphyton and fine particulate organic matter (FPOM). After the discharge point, the nutrient concentration significantly increased, and the δ15N of periphyton increased from 4.2‰ to 14.5‰. Furthermore, FPOM collected after the discharge point and suspended solids contained in wastewater effluent showed higher δ15N values than FPOM collected from the upstream section having no treated wastewater effect. In a macroinvertebrate community, an increase in δ15N was also observed for gatherers and filterers mainly feeding on FPOM after the discharge point. These results imply that the effects of treated wastewater discharge extend to consumers in the food web structure through primary production and FPOM.
