Persistence of enteric bacteria in alluvial streams

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 m(2) 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 degreesC, 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 degreesC 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.