A highly resolved, 3D model of hydrodynamics and Alexandrium fundyense in an estuarine embayment has been developed to investigate the physical and biological controls on a recurrent harmful algal bloom. Nauset estuary on Cape Cod (MA, USA) consists of three salt ponds connected to the ocean through a shallow marsh and network of tidal channels. The model is evaluated using quantitative skill metrics against observations of physical and biological conditions during three spring blooms. The A. fundyense model is based on prior model applications for the nearby Gulf of Maine, but notable modifications were made to be consistent with the Nauset observations. The dominant factors controlling the A. fundyense bloom in Nauset were the water temperature, which regulates organism growth rates, and the efficient retention of cells due to bathymetric constraints, stratification, and cell behavior (diel vertical migration). Spring-neap variability in exchange altered residence times, but for cell retention to be substantially longer than the cell doubling time, it required both active vertical migration and stratification that inhibited mixing of cells into the surface layer by wind and tidal currents. Unlike in the Gulf of Maine, the model results were relatively insensitive to cyst distributions or germination rates. Instead, in Nauset, high apparent rates of vegetative cell division by retained populations dictated bloom development. Cyst germination occurred earlier in the year than in the Gulf of Maine, suggesting that Nauset cysts have different controls on germination timing. The model results were relatively insensitive to nutrient concentrations, due to eutrophic conditions in the highly impacted estuary or due to limitations in the spatial and temporal resolution of nutrient sampling. Cell loss rates were inferred to be extremely low during the growth phase of the bloom but increased rapidly during the final phase due to processes that remain uncertain. The validated model allows a quantitative assessment of the factors that contribute to the development of a recurrent harmful algal bloom and provides a framework for assessing similarly impacted coastal systems.

中文翻译：

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河口有害藻华的温度和停留时间控制：在Nauset河口模拟水动力和亚历山大藻。

已开发出高度解析的3D模型，用于在河口内进行水动力和亚历山大藻的研究，以研究对有害藻类反复繁殖的物理和生物控制。鳕鱼角（美国马萨诸塞州）的纳瑟河口包括三个盐池，这些盐池通过浅水沼泽和潮汐网络与海洋相连。该模型使用定量技能指标针对三个春季开花期间的物理和生物学状况进行评估。在芬迪湾亚历山大藻模型是基于缅因州海湾附近先验模型的应用，但值得注意的改动做了要与瑙塞特的意见是一致的。控制A. Fundyense的主要因素水温调节着生物的生长速度，水深限制了水面温度的限制，分层和细胞行为（垂直迁移），从而调节了细菌的生长。交换中的春季小憩改变了停留时间，但要使细胞滞留时间明显长于细胞倍增时间，就需要活跃的垂直迁移和分层作用，以抑制细胞因风和潮气而混入表层。与缅因湾不同，模型结果对囊肿分布或发芽率相对不敏感。取而代之的是，在瑙塞特（Nauset），由滞留种群导致的营养细胞分裂的高表观率决定了绽放的发展。囊肿发芽的时间比缅因湾早，提示恶心囊肿对发芽时间的控制不同。该模型结果对营养物浓度相对不敏感，这是由于受到严重影响的河口处于富营养化条件，或者由于营养物采样的时空分辨率受到限制。据推断，在开花的生长阶段，细胞损失率极低，但由于过程仍不确定，在最终阶段细胞损失率迅速增加。经过验证的模型可以定量评估造成有害藻类反复繁殖的因素，并为评估受到类似影响的沿海系统提供框架。由于受到严重影响的河口处于富营养状态，或者由于养分采样的时空分辨率受到限制。据推断，在开花的生长阶段，细胞损失率极低，但由于过程仍不确定，在最终阶段细胞损失率迅速增加。经过验证的模型可以定量评估造成有害藻类反复繁殖的因素，并为评估受到类似影响的沿海系统提供框架。由于受到严重影响的河口处于富营养状态，或者由于养分采样的时空分辨率受到限制。据推测，在开花的生长阶段，细胞损失率极低，但由于过程仍不确定，在最终阶段细胞损失率迅速增加。经过验证的模型可以定量评估造成有害藻类反复繁殖的因素，并为评估受到类似影响的沿海系统提供框架。