Spatio-temporal influence on river water chemistry of Doyang river, Nagaland, India, using multivariate techniques

The study aimed to assess the spatial and seasonal variation of water chemistry along the Doyang river. Data of sixteen physicochemical parameters of water quality collected from eight sampling stations during 2016-2017 were subjected to multivariate statistical techniques like principal component analysis (PCA) and cluster analysis (CA) to address the objectives of the study. Based on the similar characteristics of water qualities, CA differentiated the study area into three different clusters or groups. The result of PCA obtained for pre-monsoon, monsoon and post-monsoon showed three PCs each explaining 94.75%, 93.63%, and 93.91% of the total variance. In each of the seasons, PC1 produced the maximum explanatory variance with over 60%. The present study found midstream stations (S2, S3, S4, and S5) experiencing much of the seasonal influence (rainfall), and parameters like WT, CO2, pH, DO and BOD were found to accord the seasonal cycle. Anthropogenic activities were found to be the main cause of pollution along the Doyang river. Accordingly, the river is segregated into three different zones based on the nature of the pollution load, i.e., mineral loading at the upstream zone, organic loading at the midstream zone, and nutrient loading at the downstream zone. Finally, the use of PCA and CA has proven effective in evaluating the complex datasets and demonstrates its usefulness in assessing the spatio-temporal variations of surface water chemistry in the Doyang river.