Water Quality Assessment of an Urban River System: Temporal and Spatial Water Quality Trends in the Mula-Mutha River,...

River pollution is a significant global concern, as rivers have served as the foundation for the expansion of civilizations since time immemorial. The drastic increase in population, rapid industrialization, and urban expansion have caused deterioration of river ecosystems, adversely impacting agriculture, human health, and biodiversity. The Mula-Mutha River is an important river in Pune as it supplies water for irrigation and drinking purposes. This study aims to assess the physicochemical parameters of river water to determine its water quality (WQ) and examine how it has changed spatially over the years. Sampling was conducted at eight sites along the river, spanning from Khadakwasla to Daund, during the period 2019-2021. Key parameters analyzed included physicochemical parameters and the concentrations of various cations and anions. This paper discusses how spatial variations influence WQ, highlighting the contributing factors. The results show that WQ deteriorates downstream as the river enters the city where sewage discharge and effluents from various industries contribute to increasing pollution level. There was a variation in physicochemical parameters and ionic concentrations, with most parameters showing an increasing trend during the period 2019-2021. However, a significant reduction in pollution was observed at certain locations in 2021. Results indicate considerable deterioration in WQ, particularly at downstream sites. In 2019, WQI values exceeding 300 at Vitthalwadi, Bundgarden, and Kharadi classified the water as unsuitable for drinking. WQI values indicated an improvement in WQ during 2020 and 2021, reflecting the positive impact of reduced anthropogenic activities during the pandemic. Iron concentrations exceeded permissible limits at all locations except Khadakwasla, suggesting downstream iron enrichment influenced by anthropogenic processes. Chloride concentrations ranged from 15.6 to 536.57 mg/L, with most sites remaining within IS 10500 limits, except Daund (2019) and Bundgarden and Daund (2021), indicating localized salinity stress. Phosphate concentrations varied from 0.33 to 43.14 mg/L, with all sites except Khadakwasla exceeding the WHO permissible limit, posing a high risk of eutrophication. Elevated chloride and phosphate levels are attributed to anthropogenic inputs such as industrial effluents, sewage discharge, and agricultural runoff. Water quality index, sodium adsorption ratio, and residual sodium carbonate values were also calculated to determine the suitability of the river water for drinking and irrigation purposes. In 2019, Vitthalwadi, Bundgarden, and Kharadi recorded WQI values exceeding 300, indicating that the water was unsuitable for drinking. The water was found to be fit for irrigation except at Pargaon and Daund, which also showed noncompliance in other physicochemical parameters as well. WQI showed improvement in WQ during 2020 and 2021, indicating a positive impact of restrictions on anthropogenic activities during the pandemic. Overall, the findings highlight significant human-induced impacts on WQ and emphasize the need for continuous monitoring and effective management strategies to safeguard water resources for drinking and irrigation purposes.