Tempo-spatial controls of total coliform and E. coli contamination in a subtropical hilly agricultural catchment

Waterborne microbial pollution remains poorly understood in developing countries, especially in rural areas. The transport of point (e.g. untreated domestic wastewater) and non-point sources of fecal bacteria such as Total coliform (TC) and Escherichia coli (E. coli) and their spatial and temporal patterns were identified in a typical small agricultural catchment in a hilly area of subtropical China. Over the sampling area, 460 water samples from 24 sites were collected during a period of 12 months, and a remediation option using an existing ecological ditch was evaluated. The results showed that 70% surface water samples exceeded the guideline of 1000 TC MPN 100 ml−1 in the catchment. Also, 90% of groundwater samples exceeded the guideline of 10 MPN E. coli 100 ml−1 for safe drinking water. Higher concentrations of TC and E. coli occurred both in the warm and rainy season in surface water and groundwater. TC and E. coli concentrations in surface water tributaries and groundwater near residential areas were greater than those in downstream water bodies. A 300 m long vegetated ecological ditch greatly reduced average concentrations TC of 97.7% and E.coli of 99.5%. TC and E. coli concentrations were significantly correlated with electrical conductivity and turbidity, both in surface water and groundwater, indicating that mixtures of organic colloids and sediment were the most important transport vector for pathogens. However, temperature only showed a controlling effect on bacteria concentration in groundwater in this particular catchment. The current research could help predict microbial risks and establish integrated management strategy to improve water quality in the hilly agricultural catchments in the subtropical region.