Effects of Extreme Flooding on Water Quality in Areas of Dense Food Animal Production

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WRRI Project;20-09-W

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Storm events are expected to increase with climate change, with the potential to adversely impact environmental quality and public health. This study assessed impacts of Hurricane Florence on water quality in areas of dense food animal production. Twelve surface water sites in rural, eastern North Carolina were sampled before and after Hurricane Florence to assess storm effects and duration of impacts. Concentrations of fecal indicator bacteria Escherichia coli were not significantly different in our first sampling event, conducted 10 days after Hurricane Florence. Instead, the longitudinal data show that first runoff events, defined as rainfall following a dry period, are associated with increased concentrations of fecal indicator bacteria in these watersheds. Additionally, watersheds with larger commercial hog operations (CHOs) and CHOs closer to sampling sites, as well as sites with larger number of households closer to sampling sites had increased E. coli concentrations. Unlike E. coli concentrations, we found that mean ranks of microbial source tracking markers associated with swine wastes (pig-2-bac) and human wastes (HF183) were higher immediately after Florence (Mann Whitney U p=0.009, p=0.0003 respectively). The swine MST marker was markedly elevated at several sites in watersheds with CHOs, while the human MST marker suggested diffuse human contamination across study sites. Antimicrobial resistance among E. coli isolated from study waters was also higher in watersheds with CHOs. Resistant E. coli was detected in 46% (n=147) of samples collected downstream of CHOs compared to 22% (n=94) of samples collected in watersheds without CHOs, resulting in a relative risk of 1.47 (95% CI: 1.21, 1.78). Bacteria with multiple antibiotic resistance was isolated in 15 of the CHO-associated samples and 1 background sample. Occurrence of AMR does not appear to be driven by precipitation, suggesting other dynamics such as spray events or antibiotic use practices may better explain contributions to resistant bacteria to surface waters. These results help clarify the effects of extreme flooding on microbial contamination of surface waters and can inform strategies for waste management, antibiotic use, and one health surveillance. Ultimately, this work contributes information to build more resilient agricultural systems and communities better prepared to weather the storms that frequent the North Carolina coast.