| dc.description.abstract | Pathogens are the leading cause of impairment for rivers and streams in the United States. Microbial contamination in recreational water bodies was the cause of 510 waterborne disease outbreaks in the United States. Water quality standards should prevent these outbreaks from occurring, however, in 93% of outbreaks, where water quality information was available, the water body was meeting water quality standards at the time of the outbreak. The probability of gastrointestinal (GI) illness from recreational exposure to human, cattle, and wildlife fecal contamination was calculated in three water bodies impaired by microbial contamination by applying Quantitative Microbial Risk Assessment (QMRA) and Microbial Source Tracking (MST). Six reference pathogens were used to estimate the probability of GI illness: Campylobacter, Cryptosporidium, E. coli O157:H7, Giardia, norovirus, and Salmonella. The largest contributor of fecal contamination within the water bodies (wildlife) had the least significant impact on human health in all three water bodies. Whereas, human fecal sources had the most significant impact on the probability of GI illness, especially through the reference pathogen norovirus. Non-point source fecal loads were spatially estimated within the Lampasas River Watershed using SELECT from three general sources: cattle, human, and non-avian wildlife. SWAT was used to simulate source specific in-stream E. coli concentrations from the fecal loads estimated by SELECT. SWAT-simulated in-stream E. coli concentrations were used to estimate reference pathogen doses which were input into a QMRA to estimate human health risk associated with exposure to fecal contamination from contact recreation in impaired waters. Across all flow conditions, the WWTP had the most significant impact on human health risk even though it was not the largest contributor to fecal contamination. The probability of GI illness associated with the WWTP exceeded the acceptable GI illness rate but the WWTP was meeting water quality regulations.
Water bodies are regulated by developing a total maximum daily load (TMDL) to determine the largest contributor of fecal contamination and make appropriate load reductions to that contributor. For regulation and remediation to have significant impacts, it should be focused on sources that are the riskiest to human health. | en |
