Analysis of seasonal spatio-temporal variations in the quality of river waters and its influencing factors in the Periyar River Basin, southern Western Ghats, India

In this study, an extensive and methodical investigation was carried out to comprehend the different geochemical processes, factors governing the hydrochemical composition and water suitability for drinking, irrigation and industrial usage in the Periyar River Basin (PRB). A total of 300 samples were collected from the mainstream, tributaries and dams of the river during PREM (Pre-Monsoon), POM (Post Monsoon), NEM (North-East Monsoon) and SWM (South-West Monsoon). The results suggested that the cationic composition is chiefly characterized by the predominant presence of Ca2+ and Mg2+ while Cl− dominates the anionic composition followed by HCO3-. The results identified transitional waters. Gibb's diagram revealed that the ionic composition dominance in the study area is influenced by the chemistry of the host rock rather than precipitation and evaporation. A comparatively greater pCO2 (>10−3.5 atm) shows an atmospheric disequilibrium in natural waterbodies due to both anthropogenic activities and input of baseflow to stream discharge. The Water Quality Index showed excellent (0–25) to unsuitable (>300) category during NEM, POM and PREM with significant spatial variation along the river. Integrated irrigational suitability indices illustrated the suitability of the samples for agricultural use, except for a few samples in the lowland region.