Determining Seasonal Pattern in Stream Water Quality: A Case Study of River Mahananda at Siliguri, West Bengal, India

Abstract

The objective of the present study is to recognize the seasonal pattern in water quality status of the stretch of river Mahananda at Siliguri Municipal Corporation of West Bengal. Monthly observations on 21 water quality parameters for the period between January, 20 IO and May, 2022 were used for resolving the present problem. The whole database was generated by West Bengal Pollution Control Board following the guideline of Central Pollution Control Board, Govt. of India. The Hierarchical Cluster Analysis was applied to determine the seasonality while Spearman's Rank correlation was used for determining the association of water quality parameters with seasonal and monthly normal rainfall total in view to capture the role of rainfall in controlling such seasonality. The result demonstrates that the temporal change in water quality status forms three specific hydrogeochemical seasons, January to May, June to August, and September to December which are governed by local rainfall pattern. Further observed that geogenic parameters e.g., Turbidity, TFS, TSS etc. completely follow seasonality of rainfall but this straight forward relation is not found for anthropogenic contaminants. Many anthropogenic parameters (e.g., Na+, EC, TA etc.) show significant negative relationship with rainfall while many of them (e.g., BOD, DO, etc.) do show any pattern at all. Since rainfall cannot fully explain the whole complexity, the role of other factors like discharge associated with hydrogeochemical seasons, needs to be evaluated in this context.