The Persistence of Riverbed Bacterial Stores and Their Disruption by Human Recreation
Orear, Ryan W.
Dalman, Nancy Eufemia
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Disturbance to riverbed sediments from human recreation allows for Escherichia coli (E. coli) to become elevated in the water column. To illustrate the role that sediment bacterial stores have in water-borne contamination, three experiments were performed. The first test was a field based bacterial sediment and water comparison designed to confirm that sediments harbor higher bacterial loads than water. Water and sediment samples were collected mid – stream during July, August, and September at five distinct locations. At recreational sites sediment displayed significantly higher E. coli levels than water; this trend did not exist at non - recreational sites with minimal sediment disturbance. The second field experiment observed the water – borne concentration of E. coli after an induced disturbance to riverbed sediment. A rake was used to disturb a plot of 2m2 riverbed and then water samples were collected over a span of 130 seconds, 10 meters downstream of the disturbance. E. coli concentrations increased 7.5 - fold and particulates increased 60 - fold in the water column 50-60 seconds after disturbance, then returned to basal levels over the next 70 seconds. The last test was a laboratory based microcosm persistence experiment. Twelve samples received ten grams of sterile sediment plus 100 ml of sterile water. The other twelve samples only received 100 ml of sterile water. All samples were inoculated with 1x106 colony forming units (CFU) of E. coli. E. coli persisted on average 5 days longer and at population densities 10 fold higher in water overlaying sediment than in water alone. E. coli in all experiments were quantified using the Colilert ® Quanti – tray 2000 system (IDEXX). These results demonstrate that sediments store bacteria for extended periods and as human recreation disturbs sediment, the risk of humans contracting a water-borne infection increases.