A Screening-Level Multi-Index Framework for Assessing Surface Water Quality Trends in the Atrato River Basin, Colombia, Under Data-Scarce Monitoring Conditions and Artisanal Gold Mining Pressure

Abstract

This study presents a screening-level multitemporal assessment of surface water quality in the Atrato River (Chocó, Colombia), a tropical river system heavily influenced by artisanal and illegal gold mining, elevated sediment loads, and untreated domestic wastewater. Using records from 20 monitoring stations (2020–2025) operated by the regional environmental authority (CODECHOCÓ), six water quality indices (ICA, ICOMO, ICOMI, ICOSUS, ICOMINERÍA, ICOTRO) were analyzed through a framework combining Theil–Sen trend estimation, Kendall’s tau correlation, inter-period median comparison, and an index orientation normalization procedure. Results suggest spatially heterogeneous patterns: organic contamination improved in 11 of 17 evaluable stations, while mining contamination (ICOMINERÍA) showed positive directional slopes in 14 of 17 evaluable stations. Of these, four middle-reach stations reached statistical significance (p < 0.05; Kendall’s τ = 0.618–0.667). At the network level, the mean ICOMINERÍA value increased from 0.191 in 2020 to 0.502 in 2025 (+163%), representing a directional signal that should be interpreted as screening-level evidence requiring confirmation through denser temporal sampling. The proposed framework provides support for potential applicability for detecting environmental change in data-scarce monitoring networks and provide screening-level evidence relevant to the enforcement monitoring of environmental rights granted under Colombia’s landmark Sentencia T-622 (2016).