Limnological dynamics in groundwater resources of Bhadra River Basin, Central Western Ghats, India: Geospatial approach

Groundwater from accessible aquifers constitutes a primary source of drinking and irrigation water in many tropical river basins; however, increasing anthropogenic pressures and geogenic controls are progressively altering its hydrochemical and microbiological integrity. In the Western Ghats region of India, systematic information on the coupled hydrogeochemical and bacteriological characteristics of accessible aquifers remains limited, particularly in highly stressed basins such as the Bhadra River Basin. In this study, the hydrobiogeochemical status of groundwater in the central Western Ghats segment of the Bhadra River Basin was evaluated during the dry season. 23 groundwater samples were collected across the basin (excluding forested zones) and analyzed for physicochemical parameters, major ions, nutrients, irrigation indices, and bacteriological indicators. Hydrogeochemical processes were interpreted using Pearson correlation analysis, Gibbs plots, and Piper diagrams, while water suitability was assessed using drinking-water standards and conventional irrigation indices. The results indicate that groundwater is predominantly fresh, low-mineralized, and recharge-controlled, with major-ion chemistry governed primarily by rock–water interaction. Most samples fall within excellent to good drinking-water categories, although localized enrichment of nutrients and dissolved ions was observed in urban and intensively cultivated zones. Irrigation indices (SAR, PI, KR, Wilcox, and USSL) show that most groundwater is suitable for irrigation; however, elevated sodium, bicarbonate, and magnesium hazards at a few locations indicate emerging risks of soil permeability loss and salinization. In contrast to generally favorable hydrochemistry, bacteriological analyses revealed widespread microbial contamination, with total coliforms and Escherichia coli detected in 19 samples and localized occurrence of Salmonella spp. (10 CFU/100 mL) and Shigella spp. (4 CFU/100 mL), indicating serious public-health concern. The findings demonstrate that although groundwater in the Bhadra River Basin is largely geogenically regulated and chemically suitable, shallow accessible aquifers are highly vulnerable to surface-derived microbial contamination driven by inadequate sanitation and land-use pressures. The study emphasizes the urgent need for integrated hydrogeochemical–microbiological monitoring, protection of recharge zones, and improved wastewater management to safeguard groundwater resources and public health in the basin. • Limnological dynamics in accessible aquifer systems in Bhadra River Basin evaluated. • Geogenic and anthropogenic activities determine the Groundwater chemistry. • The Pearson Correlation Matrix clearly pointed out correlation of dissolved solids with EC, which in turn influencing the ionic dynamics of water. • WQI and IWQI indices including multivariate statistical techniques were used for assessing sustainable ecosystem health. • Widespread E. Coli contamination observed in most of the groundwater resources.