IMCC Journal of Science

Abstract: 

Urban lakes in rapidly expanding megacities are increasingly exposed to severe organic pollution due to untreated sewage discharge and unmanaged solid waste. This study investigates seasonal variations in physicochemical water quality and associated socio-environmental responses in Dhanmondi Lake, an urban lake located in Dhaka, Bangladesh. Water samples were collected from twelve representative locations during two seasonal monitoring campaigns conducted in April 2025 (pre-monsoon) and July 2025 (monsoon), with one sampling event performed per season, and analyzed following standard methods. Key parameters included dissolved oxygen (DO), biochemical oxygen demand (BOD₅), electrical conductivity, turbidity, color, alkalinity, carbon dioxide, salinity, and iron. A structured questionnaire survey involving 200 residents was conducted to contextualize the laboratory findings. Results indicate chronic organic contamination during both monitoring periods, with mean BOD₅ concentrations of 23.33 mg/L in the pre-monsoon season and 17.0 mg/L during the monsoon season, substantially exceeding national drinking water and fisheries standards. Although monsoonal dilution reduced conductivity and alkalinity, dissolved oxygen declined to near-critical levels during the monsoon season, with a mean of 5.63 mg/L, indicating increasing oxygen stress in the lake ecosystem. Turbidity, color, and carbon dioxide concentrations consistently exceeded recommended limits, reflecting persistent organic loading. Public perception was consistent with the observed environmental degradation patterns, identifying sewage inflow and waste disposal as the dominant pollution sources. The findings indicate that Dhanmondi Lake is experiencing severe organic pollution under sustained anthropogenic pressure and provide a seasonal empirical baseline to support pollution control and restoration planning for urban lakes in rapidly urbanizing regions.

Keywords: Bangladesh; biochemical oxygen demand; dissolved oxygen; organic pollution; sewage pollution; urban lake; water quality