Seasonal upwelling and rainfall events influence estuarine communities, but their interaction is not well understood, particularly in estuaries impacted by coastal eutrophication. Here we evaluated the responses of the plankton community to multiple drivers in Guanabara Bay, a eutrophic estuary in the western Atlantic influenced by coastal upwelling. Plankton taxonomy and biomass were determined through weekly sampling over 1-year. The presence of the South Atlantic Central Water (SACW) signature was detected in the bay in half of our samples during the wet season. Importantly, SACW intrusions derived from coastal upwelling had a significant impact on plankton community composition. For microplankton, taxonomic shifts reflected in different cell sizes, with larger mixotrophic and heterotrophic taxa characterizing SACW intrusions. Larger species of copepods, including indicators of SACW, were also associated to the upwelling intrusion. Overall, plankton biomass was not explained by the SACW presence or absence alone; instead, the interaction between rainfall and upwelling was key to determine temporal variations in biomass. Our findings suggest that SACW intrusions can impact food web functioning through shifts in community composition and size depending on the relative intensity and frequency of upwelling events and rainfall. Frequent SACW intrusions might also dilute the highly eutrophic waters, with the potential to shift the metabolism of an estuary heavily impacted by eutrophication.

季节性上升流和降雨事件影响河口群落，但人们对它们的相互作用尚不甚了解，尤其是在受到沿海富营养化影响的河口中。在这里，我们评估了浮游生物对瓜纳巴拉湾的多个驱动器的反应，瓜纳巴拉湾是受沿海上升影响而在西大西洋富营养化的河口。浮游生物的分类学和生物量是通过一年以上的每周采样确定的。在潮湿季节，在海湾中的一半样本中检测到了南大西洋中央水域（SACW）签名。重要的是，源自沿海上升流的SACW入侵对浮游生物群落组成有重大影响。对于微浮游生物，分类学变化反映在不同的细胞大小中，SACW入侵具有较大的混合营养和异养分类单元。pe足类的较大种类，包括SACW的指标，也与上升流侵入有关。总体而言，SACW不能单独解释浮游生物的生物量。相反，降雨与上升流之间的相互作用是确定生物量随时间变化的关键。我们的研究结果表明，SACW入侵可能会根据上升事件和降雨的相对强度和频率，通过改变社区组成和规模来影响食物网的功能。SACW的频繁入侵也可能稀释高度富营养化的水，从而可能改变受富营养化严重影响的河口新陈代谢。降雨与上升流之间的相互作用是确定生物量随时间变化的关键。我们的研究结果表明，SACW入侵可能会根据上升事件和降雨的相对强度和频率，通过改变社区组成和规模来影响食物网的功能。SACW的频繁入侵也可能稀释高度富营养化的水，从而可能改变受富营养化严重影响的河口新陈代谢。降雨与上升流之间的相互作用是确定生物量随时间变化的关键。我们的研究结果表明，SACW入侵可能会根据上升事件和降雨的相对强度和频率，通过改变社区组成和规模来影响食物网的功能。SACW的频繁入侵也可能稀释高度富营养化的水，从而可能改变受富营养化严重影响的河口新陈代谢。