Spatial–Temporal Assessment of Urban River Contamination Dynamics: Water Quality Index and Pollution Index of Pune Metropolitan Region, India

Abstract

Aims: To evaluate Water Quality Index (WQI) and Comprehensive Pollution Index (CPI) across 13 sites of the Mula-Mutha river systems flowing through Pune Metropolitan Region, identify spatiotemporal pollution hotspots, and recommend sewage treatment plant (STP) interventions for policymakers. Study Design: A five-year observational study analysed water quality using basic statistics and advanced methods like PCA, factor analysis, correlation, and cluster analysis on physical, chemical, and biological parameters. Place and Duration of Study: The investigation was carried out along the Mula-Mutha river systems within the Pune Metropolitan Region, Maharashtra, India, spanning from January 2020 to December 2024. Methodology: 390 water samples collected from 13 sites were analysed for pH, EC, TDS, BOD, COD, DO, Cl⁻, SO₄²⁻, Mg²⁺ and other parameters using standard methods. BIS-WQI and CPI were calculated; multivariate techniques were used to identify pollution sources and spatial patterns. Results: Physicochemical parameters showed moderate alkalinity with frequent BIS limit exceedances: pH 7.36–8.06, TDS 57–633 mg/L, BOD 8.9–298 mg/L, low DO 2.8–5.2 mg/L (r=-0.44 with BOD). Mula River sites exhibited greater deterioration than Mutha. PCA explained 65.71% anthropogenic pollution variance; strong correlations included TDS-hardness (r=0.984), EC-BOD (r=0.842). Cluster analysis identified clean upstream sites (S-9, S-1) vs. downstream hotspots (S-3, S-7, S-10); WQI-CPI classified most sites as poor at urban confluences. Conclusion: The findings highlight progressive urban-induced degradation of the Mula-Mutha river system, needing prioritised installation and upgrading of STPs at identified pollution hotspots to mitigate ecological risks and safeguard public health. Study methodology applicable to global urban river systems for contamination mapping and policy intervention.