Indicator Bacteria-Sediment Relationships: Implications for Water Quality Modeling and Monitoring.
The sanitary quality of water is routinely monitored by testing for fecal coliforms and fecal streptococci (indicator bacteria). Indicator bacteria may not be pathogenic, but high levels in water suggest a greater probability for the presence of pathogenic bacteria and human health risks (Geldreich, 1990). Many bathing areas throughout the Great Lakes Basin commonly are closed due to elevated fecal coliform levels. Concern over beach closings and degraded water quality has resulted in the initiation of various remedial programs such as the Metropolitan Toronto and Region Conservation Authority's (MTRCA) Rural Beaches Project. The long term goals of the MTRCA project are to improve water quality at identified problem beaches and provide technical assistance towards improving surface water quality in all of the Authority's rural waterways (Mar, 1991).
Indicator bacteria may be concentrated in river or lake-bed sediment through deposition of bacteria-bound particles. These sediments may act as a source of nutrients, provide protection from the destructive action of sunlight and protect against predation by other microorganisms. As a result, the sediment may serve as a reservoir for enteric bacteria. Bacteria-colonized bed sediment may become resuspended by perturbations, including storm events, ship/boat passages and swimmers, thereby negatively affecting water quality.
Bacteria may colonize suspended sediment within various environments, including freshwater and combined sewer systems, and this may serve as one mechanism that generates flocculation (i.e. the joining of several discrete particles that move as a single unit). Flocculation modifies the hydrodynamic properties of the particles and this will affect the transport of particle-bound contaminants. Data collected for the Buffalo River, NY and tributaries are used to illustrate the interactions between bacteria and sediment and the implications for water quality modelling and monitoring are discussed. Specifically, the levels of indicator bacteria in riverbed sediment are examined on a seasonal and annual basis and the probability of resuspension is evaluated. The relationships between total suspended solids and bacteria levels at several sites within the Buffalo River watershed are examined through simple correlation analysis. Finally, sediment floc characteristics are examined for freshwater and sanitary sewage samples collected within the Buffalo River watershed and the role of bacteria in the flocculation of these samples is discussed.
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