Factors governing the removal of faecal indicator bacteria in the ecosystem of Lake Timsah, Egypt

Persistence of faecal coliforms, presumptive Vibrio cholerae and Vibrio parahaemolyticus at three stations in Lake Timsah were investigated in 2010. Samples were collected by day and at night. Bacterial counts were highest at the outlet of wastewater discharged into the lake (Station 1). As wastewater mixed with the lake water, bacterial counts decreased at Station 2 and were reduced by up to 90% at Station 3, approximately 1 km from Station 1. Counts of both faecal coliforms and V. cholerae were higher at night than by day. The reduction in the counts of faecal coliform bacteria in three microcosms showed that reduction of faecal coliforms was not only due to the effect of UV, but was a combined effect of both UV and predation. The microcosm experiment confirmed the importance of solar radiation over predation in reducing faecal coliform counts in aquatic environments.