Assessment of water quality and apportionment of pollution sources of an urban lake using multivariate statistical analysis

The Lake Gulshan has gained special attention to restore its water quality for public health safety, congenial lake bund, and aquatic lives as the lake is a popular recreational place and neighbourhood of critical residential and diplomatic zones. Therefore, this study assessed water quality and pollution sources of Lake Gulshan, located in the city of Dhaka in Bangladesh during dry and wet seasons, using the water quality index (WQI) rating system, Principal Component Analysis (PCA), and Positive Matrix Factorization (PMF) model. Extremely low levels of dissolved oxygen (as low as 0.2 mg/L in the dry season and 0.8 mg/L in the wet season) in the lake water suggest that it is almost impossible for any living organisms to survive. Consequently, high levels of biochemical oxygen demand (BOD, a measure of biodegradable organic matter up to 80 mg/L), Phosphate, and Nitrate (indicators of eutrophication potential as far as 5.06 mg-P/L and 228 mg-N/L) were detected in the lake water, indicating severe anthropogenic pollution. A strong correlation (Pearson with 2-tailed t-test, r = 0.85 in the dry season, r = 0.76 in the wet season, p < 0.05) between color and chemical oxygen demand (COD) demonstrates the pollution of lake water due to mixing effluent resulted from surrounding garments and dying industries. The WQI rating systems proposed by the National sanitation foundation (NSF) and the Canadian Council of Ministers of the Environment (CCME) show that the lake's water quality is in poor or bad condition and has become a growing concern for a looming ecological severe danger. Both PCA and PMF models have apportioned four factors as pollution sources in the lake water during dry and wet seasons. PCA's four factors explain 86.41% and 80.97% variances of the dataset during dry and wet seasons, respectively. PMF receptor model estimates that the point source of nutrients contributes to 42.94% of the total pollution generated by municipal wastewater discharge during the dry season. Hence, municipal waste discharges through the point sources are the leading causes of lake water pollution in the dry season. However, a non-point source of surface runoff shares 41.80% of the total pollution in the wet season generated by soil leaching runoff. This study could help the concerned authorities for the policymaking with strict regulations to protect water quality, proper management, and control pollution of the lake water.