Influence of land use/land cover on stream water quality in two watersheds in the central Andes of Bolivia: An optimised methodology

Understanding the influence of land use/land cover (LULC) on stream water quality (WQ) is essential for conservation of ecosystem services (ES) and informing sustainable land use planning. This study investigates the influence of LULC on stream WQ during the wet and dry seasons 2022–2024, across two representative watersheds in the Bolivian central Andes, a region with marked physical gradients, and external water transfers for irrigation, human consumption, and hydropower. A novel methodology was applied, combining LULC classification based on rich satellite data sources (Sentinel 1 and 2, Landsat 8), landscape characteristics, and the assessment of cumulative upstream effects on WQ across multiple spatial scale scenarios. Additionally, an anthropogenic land cover index (ALCI) was developed as a simplified indicator for WQ prediction with transferable and generalisation potential for the catchment scale. Our results revealed a strong association between cropland, built-up areas, and lawns with lower WQ parameters. In contrast, grasslands, tree cover, wetlands, and rocky areas were inverse correlated with pollution levels, particularly at the riparian and reach scales, highlighting their buffering capacity. Seasonal variation significantly influenced WQ, with greater effects at finer spatial scales. The catchment and cumulative watershed scales provided the highest predictive accuracy. Additionally, the ALCI also proved to be a promising proxy for estimating stream WQ in similar Andean environments. These findings underscore the importance of spatial configuration and natural LULC types in mitigating pollution, and support the adoption of integrated, multiscale watershed management approaches for sustaining ES in the central Andes.