The Diurnal Fluctuations and Effects of UV on Escherichia coli in Jackson, WY Recreational Streams

The concentration of Escherichia coli is used by stream monitors to gauge if a stream is safe for recreational use because an overabundance of E. coli can cause illness. The abundance of E. coli found in stream water changes throughout the day in a pattern where E. coli concentrations are highest in the morning and evening and the lowest in the afternoon. However, the reasoning for this pattern is not yet fully known. Understanding a stream's diurnal fluctuations of E. coli load and the potential causes of this pattern can be informative for stream monitoring. In this study, I observed the E. coli loads of two impaired streams, Fish Creek, and Flat Creek, located in Jackson, WY. I also, examined the role of UV radiation in determining the diurnal pattern of E. coli concentration observed in both creeks. Water samples were collected at regular intervals over 17 hours, and E. coli was enumerated using the IDEXX Colilert method. E. coli loads were found to resemble a predictable pattern. Water temperature, discharge, and UV index (UVI) values were, then, compared to E. coli loads. UVI was inversely correlated with E. coli loads and was chosen for further study. In a lab-based experiment, E. coli was exposed to no, low, and high UV. Consistent with field observations, UV intensity was found to be inversely related to E. coli concentrations. The inactivation of E. coli is caused by exposure to UV radiation, and I found the reactivation time of E. coli to be affected by UV intensity. In understanding the relationship between UV exposure and stream E. coli loads, more accurate sampling protocols to monitor streams can be created.