The impact of anthropogenic and environmental factors on the variability of Escherichia coli in rivers in southwest Bangladesh

摘要

Abstract Faecal contamination of surface water sources is an important water quality issue worldwide. Although quite a few studies exist on surface water faecal contamination and variability of indicator bacteria, most of the studies have been based on larger river basins and in temperate region. The variability is relatively unknown in local scale and in tropical developing countries. In this study, we assess how anthropogenic and environmental factors affect faecal contamination and physicochemical parameters in Rupsha and Bhairab rivers around Khulna city, Bangladesh. Water samples were collected from six locations of the rivers during a wet and dry period in 2018 to measure Escherichia coli (E. coli) concentrations applying membrane filtration method. Of the physicochemical parameters examined, turbidity, biochemical oxygen demand, and chemical oxygen demand showed higher levels of spatial variability (variation over 30). Higher concentrations of E. coli were found in the sampling sites located near the densely populated urban area compared to the downstream site, which receives fewer amounts of discharges from sewer drains. After rainfall events E. coli concentrations were increased by about one order of magnitude compared to dry weather conditions, this is in line with expectations that runoff from urban and agricultural areas brings pathogens into the rivers. All the E. coli samples violated bathing water quality standards. E. coli concentrations were found to be correlated positively with precipitation and turbidity. A linear regression model was applied, that explains large part of the variation in E. coli concentration (R2?=?0.42). Water quality index assessment also ranked the water quality as ‘poor’ category indicating high health risks involved with the water use. Therefore, the river water should not be used for domestic, recreational or bathing purposes. The study findings highlight the problem of untreated sewage discharge into the rivers. Implementation of sewage treatment plant with adequate capacity is highly recommended.