Environmental degradation in the middle basin of Conchitas river, Buenos Aires: Two decades of urban and industrial pressure

Abstract

The Conchitas River, located in the southeastern Buenos Aires Metropolitan Area, has experienced severe degradation due to two decades of unregulated urbanization, industrial effluents, and deficient wastewater management. This study aims to assess long-term changes in water quality in the middle basin of the river from 2002 to 2023. We integrated data from four historical studies with new fieldwork conducted in 2022–2023, harmonizing sampling sites, units, and parameters, evaluating physicochemical, bacteriological, and biological parameters, and complementing them with a GIS-based multitemporal land-use analysis. Despite the lack of standardization of historical data, the results revealed an urban expansion since 1998 consistent with downstream declines in water quality, with conductivity rising from 629 to 1765 µS cm−1, dissolved oxygen decreasing from 10.24 to 0.99 mg L−1, and BOD₅ peaking at 123 mg O₂ L−1. Fecal coliforms exceeded legal limits across all sites, and diatom assemblages were dominated by highly tolerant taxa. The Water Quality Index (WQI) declined from 67.7 upstream to 37.3 near the mouth. These trends highlight chronic pollution and the urgent need for integrated watershed management and investment in sanitation infrastructure.