Implications of wastewater discharges on environmental features and fish communities in an urban river

Abstract

Wastewater effluent discharges from treatment plants (WTP) are among the most pervasive stressors in urban rivers, however, their impact on the different levels of biological organization is poorly understood. This study examined the effects of wastewater effluent outflow on different trophic levels in an urban river and measured physicochemical features; bacterial, periphyton, and riparian forest composition; as well as the abundance, density, and biomass of freshwater fish at both pre- and post-WTP effluent discharge sites. Strong modification of the riparian vegetation was seen downstream from the WTP with a dominance in the richness of exotic plants. The highest values of conductivity, total bacterial composition, periphyton, and nutrients were detected in post-WTP sites. The freshwater fish recorded in the pre-WTP reaches had the highest abundance values for all species recorded. However, the exotic Brown Trout appeared to be indirectly favoured by the nutrient subsidy from the WTP discharges since the biggest individuals were recorded at post-WTP river reaches. Although the river assessed runs through an underdeveloped region in the country; our findings indicated a strong deterioration in environmental conditions and a complex relationship between the biotic responses to effluent pollution. Adequate treatment of effluent discharges is a crucial issue for urban rivers. Management actions are required because the consequences of chronic exposure on aquatic wildlife are unknown. Mostly, Patagonian aquatic systems have not yet reached an ecological tipping point, so it is recommended that restoration plans incorporate improvements in sewage treatment to avoid further degradation of ecosystem services.