Integrating Temporal and Spatial Water Quality Data for Contamination Risk Screening in a Mining-Impacted Andean River Basin: The Case of the Suratá River, Colombia

Artisanal and regulated gold-mining activity in the upper Suratá River basin (Santander, Colombia) poses a persistent threat to surface water quality, including historical mercury use and ongoing heavy-metal inputs, yet continuous, high-resolution monitoring records remain scarce in this Andean catchment. This study presents an integrated temporal and spatial assessment of water quality along the mining-influenced Suratá River. Historical physicochemical records (2015–2023) from two official monitoring stations were combined with a 2024 multi-point spatial campaign covering fourteen sites along the main channel and its tributaries (Vetas, Charta, Tona), the latter located in zones of active and historical mining. The official seven-variable Water Quality Index (WQI) methodology (IDEAM) was applied to classify sampling sites, while an Isolation Forest model identified atypical temporal patterns in the historical record. Results revealed a consistent downstream degradation gradient, with WQI values declining from the upper, mining-influenced reaches (0.67–0.68, "Regular") to the basin outlet (0.54, "Regular"), accompanied by localized exceedances of cyanide, lead, aluminum, and iron near mining-affected tributaries. Three temporal anomalies were identified among nineteen historical records. The combined use of temporal and spatial data, together with unsupervised anomaly detection, offers a low-cost, interpretable screening approach for contamination risk in mining-impacted, data-scarce river basins.