Bappa Biswas, Deepra Ghosh, Debu Mukherjee, Surajit Dutta and Sajalendu Ghosh
Abstract
The Sankh River, a major river of the Chota Nagpur Plateau, plays a vital ecological role in eastern India, yet comprehensive limnological assessments remain limited. This study reports the seasonal and spatial variations in physicochemical parameters during 2023-2024, along with water quality assessment using the Water Quality Index (WQI) and multivariate statistical analysis. Water samples were collected from five zones (Z1-Z5) during three seasons (summer, monsoon, and winter), resulting in a total of 45 samples. The seasonal variation showed that temperature, turbidity, BOD, and TDS were at their peak during the monsoon season because runoff and sediment loads increased. In winter, however, the prevailing conditions were more favourable with higher dissolved oxygen concentrations. Most parameters remained within the WHO, BIS, and CPCB permissible limits. Dissolved oxygen (>7 mg/L) and low BOD (<2 mg/ L) indicated favourable oxygen conditions and low organic pollution. Two-way ANOVA demonstrated significant seasonal variation in temperature, BOD, total alkalinity, and turbidity (p < 0.05~0.01), while spatial variation was significant for chloride, sulphate, nitrate, alkalinity, and BOD. Pearson correlation analysis showed strong positive relationships among BOD, turbidity, and nitrate, indicating organic-nutrient coupling. Hierarchical clustering identified site similarities and highlighted seasonal shifts in nutrient pollution and mineralization. During summer, monsoon, and winter, WQI values varied between 9.42~17.96, 18.74~36.92, and 11.32~18.91, respectively, classifying the river as âExcellentâ throughout except for a slight deterioration in Z5 during monsoon. These results suggest that seasonal hydrology has a stronger influence than spatial variability and that the river shows low anthropogenic stress. The findings provide baseline information on the water quality of the entire stretch of the River Sankh, which will assist river management, water quality monitoring, and freshwater ecosystem conservation.