Fish community responses to multiple municipal wastewater inputs in a watershed.

Municipalities utilize aquatic environments to assimilate their domestic effluent resulting in eutrophication, anoxia, toxicity and endocrine disruption of aquatic biota. The objective of this study was to assess the potential cumulative impacts of municipal wastewater effluent (MWWE) discharges in the Grand River on the health status of a sentinel species and the fish community downstream of 2 MWWE discharges. The fish communities downstream of the MWWE outfalls demonstrated differences in the abundance and diversity, species and family richness, % tolerance and % vulnerability when compared to the fish community upstream or further downstream of these points of effluent discharge. In both years studied, the fish community exposed to MWWE in the riffle-run habitats demonstrated reductions in the proportion of the most prominent fish (Rainbow Darter, Ethoestoma caeruleum) downstream of the outfalls, and a significant increase in the proportion of large mobile, tolerant-omnivorous fish species such as suckers and sunfish. There was less variability in the responses of the fish community to MWWE in the same season between years than between seasons within the same year. An examination of how impaired health of a sentinel species exposed to MWWE discharges parallels changes in the fish community is also conducted. This study successfully demonstrates the cumulative impact of urban development, including multiple outfalls of treated wastewater effluents on fish populations and communities. Municipalities are the major source of nutrients and pharmaceuticals and personal care products to aquatic systems, and they need to consider their impacts carefully with increasing urban population growth and ageing demographics.