The presence and abundance of Escherichia coli in beach sediment following a coastal renourishment project

Erosion poses a major threat to oceanic beaches worldwide. To combat this threat, management agencies often utilize renourishment, which supplements eroded beaches with offsite sand. This process alters the physical characteristics of the beach and can subsequently influence the presence and abundance of microbes. In this study, we examined how a renourishment project impacted sand grain size and the presence and abundance of Escherichia coli (E. coli), a common bacteria species. Using an observational field approach, we compared abundances of E. coli and sand grain sizes between non-renourished and renourished sections of Folly Beach, South Carolina, USA in 2014 and 2015. We found that E. coli was prevalent in every zone of the beach in both years of sampling. Additionally, we found that in comparison to non-renourished areas, renourished areas had significantly higher abundances of E. coli and coarser sand grains in the intertidal zone. However, these differences were temporary and only present following the initial renourishment event. Collectively, our findings raise concerns about how physical changes in sand grain size, and the introduction of offsite sand to a beach, could alter bacterial presence and growth. However, more work is needed to fully understand the timescales these effects operate upon.

Methods
The raw data was collected by methods outlined in the materials and methods section of the manuscript. Data was recorded into an Excel spreadsheet, cleaned, then uploaded into JMP Pro 14 for statistical analysis and figure creation.