Changing water quality of a major rainfed river system of western India: insights from the Bhima river using water quality index

Abstract The Bhima River originating from the Western Ghats of India, a global biodiversity hotspot, is one of the most dammed rivers, used intensively for multifaceted purposes including agriculture and domestic usage. The present study was undertaken from early pre-monsoon to start of monsoon of 2023 encompassing 68 sampling points across Bhima River and its tributaries to develop the water quality index (WQI). Environmental parameters including SWT, pH, DO, TDS and EC were measured in situ during the time of sampling. Surface water samples (1 L) was collected for estimation of dissolved nutrients. The concentration of dissolved oxygen was found to be below 2 mg l −1 in several sampling points representing hypoxic conditions of the riverine system. TDS and EC ranged from 55.12 ppm to 2983 ppm and 108.3 μS cm −1 to 5939 μS cm −1 respectively, indicating significant spatial and temporal variations. The concentration of dissolved ammonia (0.05 mg l −1 –14.09 mg l −1 ), nitrate (5.88 mg l −1 to 1596.16 mg l −1 ), o- phosphate (0.21 mg l −1 –35.47 mg l −1 ) and reactive silicate (36.70 mg l −1 to 1455.15 mg l −1 ) indicates possible influx of agricultural run-off and untreated municipal discharges. Calculations of water quality index (WQI) using the measured parameters showed ‘bad to very bad’ and ‘medium to good’ water quality along the Bhima River and its tributaries. In-depth analyses of WQI indicates pollution ‘hot-spots’ and hints toward urgent implementation of basin-level mitigation strategies for improvement of the ecological health of Upper Bhima basin.