Nutrient and Land-Use Management Effects on Water Resource Nutrient Pollution in a Hilly Watershed

The conservation and sustainable management of natural resources have become a vital part of development programmes globally. Nutrient and sediment losses from watersheds are strongly influenced by morphometry, land use, and hydrological characteristics. This study evaluates spatial patterns of water quality and nutrient transport across different reaches of the Sillahalla watershed. The watershed was stratified into three elevation-based reaches viz., lower (<2200 m), middle (2200–2400 m) and upper (2400–2630 m), and integrated grab samples were collected thrice during the monsoon period (June–August 2016). A total of 14 physicochemical parameters, including major ions and nutrient indicators, were analysed using standard laboratory procedures. Analysis of 14 physicochemical parameters revealed that most water quality indicators, including pH, electrical conductivity, total dissolved solids, and major ions, were within permissible limits for irrigation use. However, nitrate concentrations showed a progressive increase from upper (23.5 mg L⁻¹) to lower reaches (55.5 mg L⁻¹), with the lower reach exceeding the recommended limit, indicating potential risks for water quality. Elevated Biological Oxygen Demand (BOD) in the lower reach further suggested contamination from organic and anthropogenic sources. The (Nutrient Pollution Index) NPI for Nitrogen in the lower reach is 1.23 and exceeds the NPI limit of 1 indicating the potential water pollution, and the NPI for P indicates no pollution. However, the combined NPI also indicates the nutrient pollution in Lower reaches. Further, Agricultural Non-Point Source (AGNPS) model was employed to simulate nutrient losses under different management scenarios, including existing farmer practices, 25% and 50% reductions in fertilizer application, and a land-use change scenario involving partial conversion to tea plantations. Based on this result, ready reckoner for fertilizer recommendation was developed for potato and carrot with the STCR equations. This can be readily utilized by the Sillahalla watershed farmers. The study underscores the need for integrated approaches involving farmers, researchers, and policymakers to prioritise soil erosion control and sustainable land management practices. Adoption of site-specific, cost-effective, and climate-resilient soil and water conservation measures, supported by appropriate incentives, can significantly enhance on-field implementation. Overall, the research advocates for a participatory and sustainable watershed management framework to minimise nutrient losses, protect water resources, and ensure long-term agricultural sustainability in hilly regions.