Iowa Department of Natural Resources, 502 E 9th Street, Des Moines, IA 50319, USA.
Department of Agriculture and Biosystems Engineering, Iowa State University, 3358 Elings Hall, Bissell Rd, Ames, IA 50011, USA.
Sci Total Environ. 2020 Jun 20;722:137846. doi: 10.1016/j.scitotenv.2020.137846. Epub 2020 Mar 10.
Swimming advisories are commonly posted at public beaches across the United States every year. In Iowa, weekly monitoring of public swimming areas at state and county beaches have resulted in the impairment of numerous lakes for fecal indicator bacteria (FIB) contamination, as detected by E. coli. An extensive study was established to assess the relationships between E. coli contamination of nearshore beach water environments, open lake conditions and beach sands in three recreational beach/lake systems currently impaired for FIB contamination across Iowa. A transect/grab sample based sampling design was implemented across the systems with collections spanning from April through October of 2015 and 2016. Collections of E. coli along water transects identified strong near to far shore gradients of decreasing concentrations in all systems. Results indicate that concentrations of E. coli observed in swimming waters consistently disassociate with concentrations in the broader lake environment. Swimming water E. coli concentrations correlated with elevated beach sand E. coli, samples collected from beach sands uncovered concentrations up to 86,500 times higher than adjacent swimming waters. Results from this study indicate that foreshore beach sands and other beach proximate FIB sources serve as the major contributing source for swimming zone advisories. The current methodology used by state and federal officials includes impairing entire lake waterbodies for FIB contamination of the swimming area. These impairment listings do not accurately reflect the condition(s) of the larger lake environment outside the swimming area and fail to account for beach proximate conditions in the assessment process. Further, this approach provides potentially misleading information to the public and may undermine implementation strategies deployed by resource managers aimed at addressing FIB contamination at recreational swimming areas. Views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the Iowa Department of Natural Resources.
美国各地的公共海滩每年都会发布游泳建议。在爱荷华州，对州和县海滩的公共游泳区进行每周监测，结果发现由于粪大肠菌群（FIB）污染，许多湖泊的水质受到损害。为了评估爱荷华州三个娱乐海滩/湖泊系统中近海海滩水环境污染、开阔湖泊条件和海滩砂之间的关系，进行了一项广泛的研究。在这些系统中实施了基于横切/抓样的采样设计，收集时间从 2015 年 4 月到 10 月和 2016 年。在所有系统中，沿水横切的 E. coli 采集结果表明，近岸到远岸的浓度梯度呈明显下降趋势。结果表明，游泳水中观察到的 E. coli 浓度与更广泛的湖泊环境中的浓度一致。游泳水 E. coli 浓度与海滩砂 E. coli 浓度相关，从海滩砂中采集的样本中，E. coli 浓度高达游泳水的 86500 倍。本研究结果表明，前滨海滩砂和其他海滩近岸 FIB 源是游泳区建议的主要来源。州和联邦官员目前使用的方法包括因 FIB 污染整个湖泊水体而损害游泳区。这些受损清单不能准确反映游泳区以外的大湖环境状况，也没有在评估过程中考虑到海滩近岸条件。此外，这种方法向公众提供了可能产生误导的信息，并且可能破坏资源管理者为解决娱乐游泳区 FIB 污染而部署的实施策略。本文表达的观点是作者的观点，不一定反映爱荷华州自然资源部的观点或政策。
