Understanding the diversity of bacteria and E.coli levels at beaches is important for managing health risks. This study compared temporal changes of the bacterial communities of Belle Isle Beach (Detroit, MI) and Sand Point Beach (Windsor, ONT), both located near the Lake St. Clair origin of the Detroit River. Water samples collected 4 days/week for 12 weeks in summer, were subjected to 16S rRNA analysis of amplicon sequencing and E. coli enumeration. Bacterial communities changed over time, as determined by cluster dendrogram analysis, exhibiting different communities in July and August than in June and different communities at the two beaches. After June, alpha diversity decreased and relative abundance of Enterobacter (Gammaproteobacteria) increased at Sand Point; whereas, Belle Isle maintained its alpha diversity and dominance by Betaproteobacteria and Actinobacteria. Contamination at both beaches is dominated by birds (23% to 50% of samples), while only ∼10% had evidence of human-associated bacteria. High E. coli at both beaches was often associated with precipitation. Nearshore sampling counts were higher than waist-deep sampling counts. Despite the dynamic changes in bacterial communities between the two beaches, this analysis based on 16S rRNA amplicon sequencing is able to provide information about bacterial types associated with high E. coli levels and to use bacterial sequences to more precisely determine sources and health relevance of contaminants.

了解海滩细菌和大肠杆菌水平的多样性对于管理健康风险很重要。这项研究比较了位于底特律河圣克莱尔湖源头附近的贝尔岛海滩（密歇根州底特律）和沙点海滩（温莎，安大略省）细菌群落的时间变化。夏季每周 4 天收集水样，持续 12 周，对扩增子测序和大肠杆菌计数进行 16S rRNA 分析。通过聚类树状图分析确定，细菌群落随时间发生变化，显示出 7 月和 8 月与 6 月不同的群落以及两个海滩的不同群落。6 月后，α 多样性下降，肠杆菌属相对丰度（Gammaproteobacteria）在沙点增加；而 Belle Isle 通过 Betaproteobacteria 和 Actinobacteria 保持其 alpha 多样性和优势。两个海滩的污染主要是鸟类（样本的 23% 到 50%），而只有 10% 的人有与人类相关的细菌的证据。两个海滩的高大肠杆菌通常与降水有关。近岸采样计数高于腰深采样计数。尽管两个海滩之间的细菌群落发生动态变化，但这种基于 16S rRNA 扩增子测序的分析能够提供与高大肠杆菌水平相关的细菌类型的信息，并使用细菌序列更准确地确定污染物的来源和健康相关性.