Tropical watershed management: understanding the relationship between land use and pesticide pollution in Chanchaga River

Abstract

Freshwater ecosystems are vulnerable to various land use impacts, resulting in concern for aquatic biota and humans. Understanding the occurrence of pesticide contamination is necessary to safeguard aquatic biodiversity and human health. We hypothesize that sub-catchments with a higher proportion of agricultural activities have a higher concentration of pesticides in the water sample. Our study assessed the nexus between land uses and pesticide contamination in three zones of the Chanchaga River, namely, a control site, an agricultural area (S1), and an urban area (S2). Various classes of land use around the catchment were determined using ArcGIS 10.8 GIS software. At the same time, analysis of pesticide residues was carried out using the liquid–liquid extraction method, followed by gas chromatography–mass spectrometry. A total of 10 herbicides and 12 insecticides were recorded in each sampled sub-catchments, with a statistically significant difference across the sampled sub-catchments. Sampled sites in agricultural and urban areas had higher concentrations of pesticide residues than the control zone, with less anthropogenic influence. Redundancy analysis revealed farming and urbanized land use were the main sources of pesticide contamination in the waterbody. Pesticides may have chronic or acute impacts on aquatic biodiversity and a higher trophic effect on human health. It was evident that all sampled sub-catchments had pesticide concentrations exceeding the WHO permissible limit for human consumption. Prioritizing alternative methods to pesticides for managing pests and weeds is crucial for sustainable agriculture and environmental sustainability.