Influencia de tributarios (afluentes) en la calidad hídrica de los ríos de montaña.

Abstract

Mountain rivers sustain global biodiversity and providing several serve as vital sources of water for domestic use, irrigation, and other ecosystem services. However, the functionality of these ecosystems is compromised by population growth in urban areas, particularly due to waste discharges into water bodies, which result in a decline in physicochemical and biological quality as well as self-purification capacity. In the Cuenca city operates a wastewater treatment plant (WWTP) and marginal interceptors along its rivers have been implemented; nevertheless, approximately 5% of untreated wastewater continues to be discharged into receiving water bodies. This study aimed to determine the influence of tributaries exposed to varying levels of contamination on the physicochemical and biological quality of high Andean rivers. Fifteen monitoring stations were distributed in three zones of the Tomebamba and Yanuncay river sub-basins. At each station environmental variables were recorded, and six macroinvertebrate samples were collected to asses water quality. Multivariate analyses revealed a progressive decline of ecological conditions in both tributaries and the main river channel. This trend was associated with the distribution and pollution sensitivity of macroinvertebrate taxa. More sensitive taxa were associated with less polluted areas characterized by higher dissolved oxygen (DO) concentrations and lower electrical conductivity (EC) and turbidity (Turb), whereas more tolerant taxa occurred in zones with higher pollutant loads. Furthermore, linear regression analysis showed the absence of ecological recovery processes. In conclusion, this study demonstrated a progressive decline in water quality from the upper to the lower zones, marked by the loss of sensitive species and an increase in pollution-tolerant organisms. These changes are driven by variations in physicochemical parameters and susteined environmental stress.