In this study, a tracer bacteria was used to investigate the resuspension and persistence of sediment-associated bacteria in a small alluvial stream. The study was conducted in Swan Creek, located within the Grand River watershed of Ontario, Canada. A 1.1-m2 section of the bed was seeded with a strain of Escherichia coli resistant to nalidixic acid (E. coli NAR). The survival, transport, and redistribution of the tracer bacteria within a 1.7-km river section downstream of the source cell was assessed for a 2-mo period following the introduction of the tracer bacteria. This study has illustrated that enteric bacteria can survive in bed sediments for up 6 wk and that inactivation of the tracer bacteria resembled typical first-order decay. Critical conditions for resuspension, as well as resuspension rates, of sediment-associated bacteria were determined for several storm events. The critical shear stress for E. coli NAR resuspension in Swan Creek ranged from 1.5 to 1.7 N m(-2), which is comparable with literature values for critical shear stresses for erosion of cohesive sediments. Bacteria resuspension was primarily limited to the rising limb of storm hydrographs implying that a finite supply of sediment-associated bacteria are available for resuspension during individual storm events. The information presented in this paper will further the development of representative microbial water quality models.

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A tracer-bacteria was used to study the persistence of enteric bacteria in three alluvial streams (Carroll Creek, Lutteral Creek, Eramosa River) located in Southern Ontario, Canada. Within each stream, a 1.1 m2 section of the bed was seeded with a strain of Escherichia coli resistant to nalidixic acid (E. coli NAR). The survival of the tracer-bacteria within the stream bed and the release of the tracer-bacteria to the water column were monitored for approximately 3 weeks. Survival dynamics were also studied in each stream using dialysis tubes. In Carroll Creek, where water temperatures were typically lower than 16 °C, the inactivation of the tracer-bacteria did not follow a first order decay. The number of tracer-bacteria within the stream bed did not decrease for the first 5 d of the experiment. Inactivation of the tracer-bacteria within bed sediments of Lutteral Creek and the Eramosa River resembled typical first order decay, preceded by a 24-h lag phase. Water temperatures in Lutteral Creek and the Eramosa River were generally 10 °C higher than in Carroll Creek. Downstream water quality monitoring indicated that the tracer-bacteria was being released from the seeded bed sediments during both baseflow and stormflow periods in Carroll and Lutteral Creeks. However, in the Eramosa River, where bed sediments possessed an organic matter content of 9.5%, the tracer-bacteria was rarely recovered in downstream water samples. Survival dynamics observed in dialysis tubes resembled those observed in bed seeding experiments. The experimental approach employed in this study could be used to further investigate the survival and transport characteristics of sediment-associated bacteria. Key words: E. coli, sediments, survival, streams, tracer-bacteria.

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