Abstract Hembre, LK. 2019. Effects of a rainbow trout stocking moratorium on the Daphnia species composition and water quality of Square Lake (Minnesota). Lake Reserv Manage. 35:127–139. Square Lake is among the clearest lakes in the Minneapolis–St. Paul (Minnesota) metropolitan area, but its water clarity has decreased over the past several decades despite levels of total phosphorus (TP) remaining relatively stable. Predation by zooplanktivorous rainbow trout annually stocked since the early 1980s was hypothesized to be the cause for this eutrophication trend. To evaluate this hypothesis, a 3-year moratorium on trout stocking was imposed by the Minnesota Department of Natural Resources (MNDNR) and water quality and zooplankton monitoring data from 2 years prior to the moratorium (2010 and 2012) were compared to data from the 3 moratorium years (2013–2015). Significant changes observed during the moratorium years that support the hypothesis include (1) an increase in biomass concentrations of the large-bodied Daphnia pulicaria, (2) a coincident decrease in biomass concentrations of the smaller bodied D. mendotae, and (3) more pronounced spring clear-water phases when D. pulicaria reached peak densities. In addition, the volume of hypoxic water (dissolved oxygen [DO] < 1 mg/L) that developed in deep water was less in moratorium years compared to the premoratorium years. Unexpectedly, surface water TP concentrations were significantly lower during the moratorium years than in premoratorium years. Greater sequestration of P in the biomass of Daphnia during the moratorium years is the likely cause for the decrease in surface water TP levels in those years. Natural resource managers from the MNDNR have extended the moratorium and are using the conclusions from this study to determine the future fisheries management plan for Square Lake.

中文翻译：

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暂停放养虹鳟鱼对方形湖（明尼苏达州）水蚤种类组成和水质的影响

摘要 Hembre，LK。2019. 暂停放养虹鳟鱼对 Square Lake（明尼苏达州）水蚤物种组成和水质的影响。湖泊保护区管理。35:127-139。Square Lake 是明尼阿波利斯-圣路易斯最清澈的湖泊之一。圣保罗（明尼苏达州）大都市区，但尽管总磷 (TP) 水平保持相对稳定，但在过去的几十年里，其水质透明度有所下降。假设自 1980 年代初以来每年放养的浮游动物虹鳟鱼捕食是造成这种富营养化趋势的原因。为了评估这个假设，明尼苏达州自然资源部 (MNDNR) 暂停了 3 年的鳟鱼放养，并将暂停前 2 年（2010 年和 2012 年）的水质和浮游动物监测数据与 3 个暂停年（2013 年）的数据进行了比较–2015）。在支持该假设的暂停年份中观察到的显着变化包括 (1) 大体羽蚤的生物量浓度增加，(2) 体型较小的门多科的生物量浓度同时下降，以及 (3) 更多当 D. pulicaria 达到峰值密度时，明显的春季清水阶段。此外，与暂停年份相比，暂停年份在深水中形成的缺氧水量（溶解氧 [DO] < 1 mg/L）较少。不料，地表水总磷浓度在暂停年明显低于暂停年。在暂停年份期间，水蚤生物量中磷的更大封存可能是这些年份地表水总磷水平下降的原因。MNDNR 的自然资源管理人员已经延长了暂停期限，并正在利用这项研究的结论来确定 Square Lake 未来的渔业管理计划。