As sentinels of climate change and other anthropogenic forces, freshwater lakes are experiencing ecosystem disruptions at every level of the food web, beginning with the phytoplankton, a highly responsive group of organisms. Most studies regarding the effects of climate change on phytoplankton focus on a potential scenario in which temperatures continuously increase and droughts intersperse heavy precipitation events. Like much of the conterminous United States in 2019, the Muskegon River watershed (Michigan, USA) experienced record-breaking rainfall accompanied by unusually cool temperatures, affording an opportunity to explore how an alternate potential climate scenario may affect phytoplankton. We conducted biweekly sampling of environmental variables and phytoplankton in Muskegon Lake, a Great Lakes Area of Concern that connects to Lake Michigan. We compared environmental variables in 2019 to the previous eight years using long-term data from the Muskegon Lake Observatory buoy, and annual monitoring excursions provided historical phytoplankton data. Under cold and wet conditions, diatoms were the single dominant division throughout the entire growth season – an unprecedented scenario in Muskegon Lake. In 10 of the 13 biweekly sampling days in 2019, diatoms comprised over 75% of the phytoplankton community in the lake by count, indicating that the spring diatom bloom persisted through the fall. Additionally, phytoplankton seasonal succession and abundance patterns typically seen in this lake were absent. In a world experiencing reduced predictability, increased variability, and regional climate anomalies, studying periods of extreme weather events may offer insight into how natural systems will be affected and respond under future climate scenarios.

作为气候变化和其他人为力量的哨兵，淡水湖在食物网的各个层面都在经历生态系统破坏，从浮游植物开始，浮游植物是一种高度敏感的生物群。大多数关于气候变化对浮游植物影响的研究都集中在温度持续升高和干旱穿插强降水事件的潜在情景上。与 2019 年美国本土的大部分地区一样，马斯基根河流域（美国密歇根州）经历了破纪录的降雨，伴随着异常凉爽的气温，为探索替代性潜在气候情景如何影响浮游植物提供了机会。我们每两周对马斯基根湖的环境变量和浮游植物进行采样，与密歇根湖相连的五大湖区。我们使用来自马斯基根湖天文台浮标的长期数据将 2019 年与前八年的环境变量进行了比较，年度监测远足提供了历史浮游植物数据。在寒冷和潮湿的条件下，硅藻是整个生长季节中的单一优势区 - 这是马斯基根湖前所未有的情况。在 2019 年的 13 个双周采样日中，有 10 天硅藻占湖中浮游植物群落的 75% 以上，表明春季硅藻水华持续到秋季。此外，该湖中常见的浮游植物季节性演替和丰度模式不存在。在一个可预测性降低、可变性增加和区域气候异常的世界中，