Escherichia coli and fecal coliforms in freshwater and estuarine sediments

Authors: Pachepsky, Yakov; Shelton, Daniel

Submitted to: Critical Reviews in Environmental Science Technology
Publication Type: Review Article
Publication Acceptance Date: 9/3/2009
Publication Date: 5/4/2011
Citation: Pachepsky, Y.A., Shelton, D.R. 2011. Escherichia coli and fecal coliforms in freshwater and estuarine sediments. Critical Reviews in Environmental Science Technology. 41(12):1067-1110.

Interpretive Summary: Microbial water quality of surface waters is evaluated by measuring the concentrations of the indicator bacteria such as fecal coliform bacteria (FC), or more recently E. coli. Elevated FC or E. coli concentrations indicate possible fecal contamination that are commonly attributed to the influx of fecal material to water with runoff or groundwater, or from direct contamination of water with feces from mammals, birds, or humans. The fact that streambed or bottom sediments can harbor substantial E. coli populations is well known but almost universally ignored when it comes to the interpretation of high E. coli concentrations in water and to the development of management strategies to alleviate the microbial impairment of water sources. This manuscript is the first comprehensive single-source review of existing information about E. coli concentrations in sediments and adjacent soils. This review demonstrates both the importance of E. coli reservoirs in bottom sediments and the massive knowledge gap that requires serious attention. Sediments can contain and support very large and genetically diverse populations of E. coli that may include pathogenic strains. The release of these bacteria with resuspended sediments can create elevated concentrations in water far above regulatory thresholds. Environmental parameters that can affect survival of E. coli in sediment are listed and their effect is documented. Current microbial water quality models, used to support management decisions, ignore the sediment E. coli input. The implications for monitoring and management of microbiological water quality are discussed. Results of this work are essential for regulators as well as scientists and practitioners involved in the design, evaluation and implementation of conservation and best management practices nationwide in that the work has identified and characterized important sources of water quality indicator bacteria in surface waters.

Technical Abstract: It has been known for some time that substantial populations of fecal coliforms and E. coli are harbored in freshwater bottom sediments, bank soils, and beach sands. However, the relative importance of sediments as bacterial habitats and as a source of water-borne fecal coliforms and E. coli has not been recognized until recently when a large number of publications have shown that in many cases the resuspension of sediment, rather then runoff from surrounding lands, can create elevated E. coli concentrations in water. This review is an attempt to develop the first comprehensive single source of existing information about fecal coliforms and E. coli in sediments and adjacent soils and to outline the knowledge gaps and research needs. The review summarizes available information on variability and environmental correlations of E. coli and FC concentrations in sediments, genetic diversity of E.coli in sediments, survival of E. coli and FC in sediments, release with resuspended sediment and settling of E. coli and FC, modeling of sediment effects on fate and transport of E. coli in surface waters, and implications for monitoring and management of microbiological water quality. The demonstrated role of pathogenic E. coli strains in food and water quality challenges reinforces the need in better understanding ecological and hydrological factors that affect functioning of sediments as E. coli reservoirs.