Physicochemical characterization and ecological risk evaluation of surface water in a Himalayan foothill river system: A case study of the Charju River, India

Abstract

The Charju River is an important freshwater resource for communities in Deomali, Arunachal Pradesh, yet its hydrochemical characteristics and environmental status remain poorly documented. This study presents an integrated assessment of physicochemical characteristics, hydrochemical controls, drinking-water suitability, and screening-level ecological risk across five representative river locations. Water samples were analyzed for physicochemical parameters and major ionic constituents and evaluated using BIS standards, the Water Quality Index (WQI), Risk Quotient (RQ), Gibbs diagram, Pearson correlation, one-way ANOVA, and GIS-based spatial analysis. Considerable spatial heterogeneity was observed, with S4 emerging as a major water-quality hotspot due to elevated pH, fluoride, sulfate, sodium, suspended solids, and reduced dissolved oxygen, while S3 exhibited pronounced nutrient and bromide enrichment. WQI values ranged from 377.38 to 481.62, classifying all locations as unsuitable for direct drinking, with S3 recording the highest deterioration. Screening-level RQ analysis identified ammoniacal nitrogen, sodium, bromide, dissolved oxygen deficit, chloride, suspended solids, and fluoride as the principal contributors to moderate ecological stress, whereas BOD and COD indicated limited organic pollution. Gibbs analysis demonstrated predominant rock-weathering control, while correlation, ANOVA, and spatial patterns supported hydrogeochemical control modified by localized domestic activities, agricultural runoff, and catchment disturbances. The findings establish an important baseline for this understudied Himalayan Foothill River and emphasize the need for seasonal monitoring, source-specific pollution control, protection of riparian zones, and appropriate treatment before potable use. The integrated framework supports SDG 6 (Clean Water and Sanitation), SDG 3 (Good Health and Well-being), and SDG 15 (Life on Land) through evidence-based freshwater protection and watershed management.