Impact of agro-industrial expansion on heavy metal contamination in water resources of a poorly gauged basin.

Rapid agro-industrial growth has intensified the heavy metal contamination in ungauged regions through changing land use and water quality. It is still unclear how to continuously monitor heavy metal pollution when it is influenced by urban wastewater, agricultural runoff, and industrial discharge. This study assesses the effects of agriculture and industrial expansion on water resources by combining hydrogeochemical assessment, hydrological modeling, and land-use change analysis. Remote sensing data were used to evaluate land-use change from 2005 to 2023, while a hydrological model was developed for the period of 2010-2023 to quantify variations in the water balance components. Seasonal water sampling was conducted across 64 sites in 2023, and samples were analyzed for heavy metals, major ions, and physicochemical parameters. The results indicate that between 2005 and 2023, built-up areas expanded by 1.5%, and agricultural land increased by 0.5%, leading to a 2% reduction in bare land and increased pressure on water supplies. Hydrological modeling revealed that intensified water extraction for industrial and irrigation purposes reduced groundwater recharge by approximately 40%, resulting in a corresponding 41% decline in water yield. These hydrological alterations have exacerbated regional water quality degradation. Water quality analysis showed that aluminum concentrations exceeded permissible limits in all samples during the pre-monsoon season. In contrast, elevated manganese concentrations were detected in all groundwater samples and 96% of surface water samples. Post-monsoon analysis further revealed widespread cadmium and mercury contamination in groundwater, with mercury exceeding safe limits in all samples. Among major ions, nitrate concentrations exceeded permissible limits in 64% of surface water and 12% of groundwater samples, while pH values ranged between 5.5 and 9.1. Collectively, these findings indicate that the reductions in regional water availability are associated with changing land-use patterns that are seasonally regulated and help in driving heavy metal movement across the region. This emphasizes the need for strengthened pollution control strategies, improved wastewater treatment infrastructure, and awareness of water management among stakeholders.