ABSTRACT: Understanding the influence of biotic and abiotic factors on riverine phytoplankton dynamics is challenging, particularly as anthropogenic stressors such as eutrophication, invasive species, and climate change alter these relationships. We examined a 14 yr (January 2005 to December 2018) dataset of phytoplankton and water quality variables, along with zooplankton and nutrient concentrations, from the Columbia River (the largest river in the US Pacific Northwest) to identify seasonal and interannual patterns of phytoplankton assemblage structure and their environmental associations. Non-metric multidimensional scaling, cluster, and indicator species analyses revealed: (1) a diatom/flagellate cluster in spring/summer, associated with chlorophyll a, discharge, ciliates, and Sarcodina; (2) a cyanobacteria/chlorophyte cluster in late summer/early fall, associated with higher water temperatures, increased clarity, the invasive copepod Pseudodiaptomus forbesi, and veligers of the invasive Asian clam Corbicula fluminea; and (3) a mixed-taxa winter cluster of minimal abundance and biomass. Nutrients were not strongly associated with the observed structural patterns. Phytoplankton bloom duration varied interannually, between years with short springtime blooms vs. years when blooms extended across multiple months. Springtime blooms of the diatom Asterionella formosa decreased in recent years, giving way to blooms of a mixed diatom assemblage. Further, high temperature, low discharge, and more invasive zooplankton were associated with cyanobacterial blooms, suggesting that increased temperature and reduced river flows predicted due to climate change in the Pacific Northwest may lead to further impacts on the late summer/early fall Columbia River plankton community.

中文翻译：

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哥伦比亚河下游浮游植物的季节性和年际变化（2005-2018）：环境变化和形成大型水华的硅藻减少

摘要：了解生物和非生物因素对河流浮游植物动力学的影响具有挑战性，特别是当富营养化、入侵物种和气候变化等人为压力因素改变了这些关系时。我们检查了来自哥伦比亚河（美国太平洋西北部最大的河流）的 14 年（2005 年 1 月至 2018 年 12 月）浮游植物和水质变量的数据集，以及浮游动物和养分浓度，以确定浮游植物组合的季节性和年际模式结构及其环境关联。非度量多维标度、集群和指示物种分析揭示：(1) 春季/夏季的硅藻/鞭毛藻集群，与叶绿素a 相关、放电、纤毛虫和肉蚧；(2) 夏末/初秋的蓝藻/叶绿体集群，与较高的水温、增加的透明度、入侵的桡足类Pseudodiaptomus forbesi和入侵的亚洲蛤蜊Corbicula fluminea 的 veligers 相关；(3) 具有最小丰度和生物量的混合类群冬季集群。营养素与观察到的结构模式没有很强的相关性。浮游植物开花持续时间每年都不同，春季开花时间短的年份与开花时间跨度多的年份之间。硅藻Asterionella formosa 的春天绽放近年来减少，让位于混合硅藻组合的绽放。此外，高温、低排放和更具侵入性的浮游动物与蓝藻大量繁殖有关，这表明由于太平洋西北部气候变化而预测的温度升高和河流流量减少可能会进一步影响夏末/初秋哥伦比亚河浮游生物社区。