Assessment of Seasonality of Stream Water Quality: a Case Study of River Kaljani in Alipurduar Municipality, West Bengal, India

In this study an attempt was made to determine the seasonality of stream water quality: A case study of river Kaljani in Alipurduar Municipality, West Bengal, India. Monthly observations of 21 water quality parameters for the periods between January 2010 and December 2022 were used as the database which was generated by West Bengal Pollution Control Board in accordance with the guideline established by the Central Pollution Control Board, Govt. of India. The Hierarchical Cluster Analysis (HCA) was applied to assess the seasonal pattern in water quality status while Spearman’s Rank Correlation was used for determining the association between water quality parameters with seasonal and monthly normal rainfall to determine the impact of rainfall in controlling such seasonality. The result of HCA shows that stream water quality changes following two distinct hydrogeochemical seasons, November to April and May to October which are governed by local rainfall. The result of Spearman’s rho displays that geogenic parameters (e.g., TSS, TFS, Turbidity etc.) follow rainfall-based seasonality while anthropogenic parameters (e.g., BOD, COD, Na ⁺ etc.) do not follow rainfall-based seasonality. Since rainfall cannot fully explain the whole complexity of hydrogeochemical season, the role of other factors like discharge needs to be incorporated in this context.