Partitioning and fate of particle-associated E. coli in river waters.

Attachment of fecal bacteria to suspended matter in the water column has important implications for its fate in rivers. We examined the part of Escherichia coli (E. coli) associated with suspended matter in natural river water samples, using a combination of 5-microm filtration and beta-D-glucuronidase (GLUase) assay to estimate the E. coli abundance and attachment. We observed that the fraction of particle-associated E. coli was positively correlated with suspended matter concentration. The settling rate of particle-associated E. coli was found to be positively correlated with suspended matter concentration for samples with suspended matter content lower than 50 mg/L. For samples with higher suspended matter concentration, the settling rate was quite constant (0.066 m/h, on average). In batch experiments using river waters, we observed that free E. coli had a decay rate approximately 2 times higher than particle-associated E. coli. This information can be used to improve the models on the fate of E. coli in rivers.