Abstract
The Subarnarekha River is a critical hydro-ecological corridor of eastern India, supporting diverse ecological functions while supplying water for domestic, agricultural, and industrial use. Rapid urbanization, industrial expansion, and rising anthropogenic pressure have raised concerns over its deteriorating water quality, particularly within Ranchi district. This study evaluated the spatial variation in physicochemical characteristics of the river at eight strategically selected locations, representing upstream agricultural reaches, urban settlements, industrial zones, reservoir and waterfall segments, and downstream recovery reaches, during the pre-monsoon season (April–May 2026). Fourteen physicochemical parameters were monitored as indicators of river health. pH, temperature, total dissolved solids, salt percentage, salinity, and electrical conductivity were measured in situ, while dissolved oxygen, biochemical oxygen demand, free carbon dioxide, total alkalinity, total hardness, calcium and magnesium hardness, and chloride were determined in the laboratory, following standard APHA and IS 3025 protocols. Spatial variability was assessed using descriptive statistics, and measured values were compared against Bureau of Indian Standards (IS 10500:2012) and Central Pollution Control Board criteria to determine ecological condition and pollution status.
Results revealed wide spatial variation across stations and marked water quality deterioration in reaches influenced by industrial, urban, and suburban growth. Upstream stations at Nagri and Dhurwa showed comparatively good water quality, with low dissolved solids, higher dissolved oxygen, and lower biochemical oxygen demand. Stations within urban and industrial stretches, particularly Chutia, Namkum, and Tatisilwai, recorded elevated electrical conductivity, dissolved solids, alkalinity, hardness, free carbon dioxide, and biochemical oxygen demand alongside reduced dissolved oxygen, indicating substantial anthropogenic influence. Downstream stations at Getalsud, Hundru, and Muri showed partial recovery, suggesting natural self-purification. Ecological threat assessment classified Nagri and Dhurwa as low-risk, Getalsud, Hundru, and Muri as moderately threatened, Namkum and Tatisilwai as high-risk, and Chutia as the principal pollution hotspot exhibiting critical degradation. By characterizing the physicochemical profile of each site individually, the study identifies the principal stressors driving water quality decline in specific reaches and pinpoints where remedial action is needed. The findings underscore the value of site-specific monitoring and support targeted, localized intervention and effluent treatment strategies for the conservation and management of the Subarnarekha River basin.