Anthropogenic pressures and ecological quality gradients in rivers of the Colombian Orinoquia foothills

Abstract

Water quality in rivers is essential for food security, public health, and various ecosystem services in both urban and rural contexts; however, this aspect remains largely understudied in the piedmont region of the Llanos within Colombia’s Orinoco basin. This study aimed to assess water quality in the Ocoa, Quenane, and Guayuriba rivers and examine its relationship with biotic and abiotic variables across different hydrological periods. Abiotic indices (ICA, ICOMO, ICOTRO) and biotic indices (BMWP/Col) were applied, along with Generalized Linear Models (GLMs) to analyze the influence of land use and hydrological periods. A longitudinal gradient of water quality deterioration was observed, mainly due to urbanization, agriculture, and tourism activities, particularly during the low-precipitation period. Stations in the upper basin showed better water quality, while those in the middle and lower basins displayed signs of organic matter enrichment. GLM results indicated that infrastructure and transportation land use, nitrate concentrations, and temperature significantly affected species richness and the BMWP/Col index. The integration of physicochemical and biotic indices, along with multivariate analysis, proves to be a powerful tool for monitoring environmental impacts in rivers of the Colombian piedmont region.