Seasonal variation, spatial patterns, and environmental correlates of fecal coliform in two urban drainage channels in Sylhet, Bangladesh

Graphical abstract summarizing a study of fecal coliform (FC) contamination in the Malni Chara Drainage System (MDS) and Goali Chara Drainage System (GDS) in Sylhet City Corporation. The study included 31 sampling sites in each drainage system during pre-monsoon February and post-monsoon October, with FC analyzed using Compact Dry CF kits. Key findings show significantly higher FC concentrations in the pre-monsoon season than in the post-monsoon season in both systems, and higher FC levels in MDS than GDS during both seasons. FC showed a negative correlation with pH, a positive correlation with turbidity, and mostly positive correlations with electrical conductivity. The abstract highlights the need for improved sewage management, regular water-quality monitoring before the monsoon, and evidence-based actions to protect public health. Urban drainage systems in rapidly growing South Asian cities often convey untreated wastewater, posing environmental and public-health risks. We assessed seasonal, spatial, and physicochemical controls on fecal coliform (FC) contamination in two urban channels – the Malni Chara Drainage System (MDS) and Goali Chara Drainage System (GDS)—in Sylhet City, Bangladesh. Water was sampled at 62 stations in pre- and post-monsoon periods; FC, turbidity, pH, and electrical conductivity (EC) were measured. Descriptive statistics, non-parametric tests, spatial interpolation, and Spearman's rank correlations were used. FC showed strong seasonality, with significantly higher pre-monsoon concentrations in both systems (p < 0.001). Microbial loads were consistently higher in MDS than GDS. Interpolation maps revealed marked heterogeneity, with persistent midstream and downstream hotspots in MDS, whereas GDS had lower FC and stronger post-monsoon attenuation. log10 FC correlated positively with turbidity (ρ = 0.661–0.819, p < 0.01) and EC (ρ = 0.495–0.634, p < 0.01), and negatively with pH (ρ = −0.567 to −0.770, p < 0.01). Overall, the findings highlight seasonal modulation, drainage-specific contrasts, and environmental correlates of fecal contamination, supporting integrated spatial–statistical hotspot identification and targeted monitoring in data-scarce, monsoon-dominated urban environments.