The Maumee River is the primary source for nutrients fueling seasonal Microcystis-dominated blooms in western Lake Erie’s open waters though such blooms in the river are infrequent. The river also serves as source water for multiple public water systems and a large food services facility in northwest Ohio. On 20 September 2017, an unprecedented bloom was reported in the Maumee River estuary within the Toledo metropolitan area, which triggered a recreational water advisory. Here we (1) explore physical drivers likely contributing to the bloom’s occurrence, and (2) describe the toxin concentration and bacterioplankton taxonomic composition. A historical analysis using 10-years of seasonal river discharge, water level, and local wind data identified two instances when high-retention conditions occurred over ≥ 10 d in the Maumee River estuary: in 2016 and during the 2017 bloom. Observation by remote sensing imagery supported the advection of cyanobacterial cells into the estuary from the lake during 2017 and the lack of an estuary bloom in 2016 due to a weak cyanobacterial bloom in the lake. A rapid-response survey during the 2017 bloom determined levels of the cyanotoxins, specifically microcystins, in excess of recreational contact limits at sites within the lower 20 km of the river while amplicon sequencing found these sites were dominated by Microcystis. These results highlight the need to broaden our understanding of physical drivers of cyanobacterial blooms within the interface between riverine and lacustrine systems, particularly as such blooms are expected to become more prominent in response to a changing climate. Cyanobacterial harmful algal blooms (CHABs) have become a common seasonal occurrence in the western basin of Lake Erie and its embayments (Bullerjahn et al. 2016). Whereas the Maumee River and its watershed serve as an important source for the nutrients that fuel these blooms (Baker et al. 2014; Kane et al. 2014), CHABs in the river are sparsely documented (Bridgeman et al. 2012; Conroy et al. 2014; McKay et al. 2018). Further, when cyanobacterial blooms have been documented in the river, they have occurred in spring or early summer with late summer blooms being less common (Bridgeman et al. 2012; Conroy et al. 2014; McKay et al. 2018). The Maumee River drains into Lake Erie, forming a freshwater estuary that is influenced by riverine and lacustrine processes within the Toledo (OH) metropolitan area (Herdendorf 1970). On 20 September 2017, reports emerged of a CHAB developing within the Maumee River estuary, prompting the Toledo-Lucas County Health Department to issue a recreational public health advisory to avoid contact. The Maumee River serves as source water for multiple Ohio public water systems including the communities of Napoleon, Bowling Green, and Defiance as well as *Correspondence: timdavi@bgsu.edu This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Additional Supporting Information may be found in the online version of this article. Present address: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Present address: Biology and Environmental Sciences Department and National Center for Water Quality Research, Heidelberg University, Tiffin, Ohio, USA Present address: College of Food, Agriculture, and Environmental Sciences, The Ohio State University, Columbus, Ohio, USA

中文翻译：

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促进五大湖主要支流产毒蓝藻大量繁殖的物理驱动因素

莫米河是伊利湖西部开放水域中以微囊藻为主的季节性水华的主要养分来源，尽管这种水华在河中并不常见。这条河还是俄亥俄州西北部多个公共供水系统和大型食品服务设施的源水。2017 年 9 月 20 日，据报道托莱多市区内的莫米河河口出现前所未有的水华，引发了休闲用水咨询。在这里，我们 (1) 探索可能导致水华发生的物理驱动因素，以及 (2) 描述毒素浓度和浮游细菌分类组成。使用 10 年季节性河流流量、水位和当地风数据的历史分析确定了两个实例，其中高滞留条件发生在 Maumee 河口 ≥ 10 天：在 2016 年和 2017 年开花期间。遥感图像观测支持 2017 年蓝藻细胞从湖泊平流进入河口，2016 年由于湖中蓝藻水华较弱，河口没有水华。2017 年水华期间的一项快速响应调查确定，在河流下游 20 公里范围内的地点，蓝藻毒素（特别是微囊藻毒素）的水平超过了休闲接触限制，而扩增子测序发现这些地点以微囊藻为主。这些结果突出表明需要扩大我们对河流和湖泊系统之间界面内蓝藻水华的物理驱动因素的理解，特别是因为随着气候变化，这种水华预计会变得更加突出。蓝藻有害藻华 (CHAB) 已成为伊利湖西部盆地及其海湾地区常见的季节性事件（Bullerjahn 等人，2016 年）。尽管 Maumee 河及其流域是促进这些水华爆发的营养物质的重要来源（Baker 等人，2014 年；Kane 等人，2014 年），但该河中的 CHAB 的记录却很少（Bridgeman 等人，2012 年；Conroy 等人） . 2014 年；麦凯等人，2018 年）。此外，当记录到河流中出现蓝藻水华时，它们发生在春季或初夏，而夏末水华较少见（Bridgeman 等人，2012 年；Conroy 等人，2014 年；McKay 等人，2018 年）。莫米河汇入伊利湖，形成一个淡水河口，受托莱多 (OH) 大都市区内河流和湖泊过程的影响（Herdendorf 1970）。2017 年 9 月 20 日，有报道称，莫米河河口内出现了 CHAB，促使托莱多-卢卡斯县卫生局发布休闲公共卫生建议，以避免接触。Maumee 河是多个俄亥俄州公共供水系统的源水，包括 Napoleon、Bowling Green 和 Defiance 社区以及*通讯录：timdavi@bgsu.edu 这是一篇基于知识共享署名许可条款的开放获取文章，允许在任何媒体中使用、分发和复制，前提是原始作品被正确引用。可以在本文的在线版本中找到其他支持信息。现地址：美国田纳西州橡树岭橡树岭国家实验室环境科学部现地址：