Cooperative Institute for Great Lakes Research, School for Environment and Sustainability, University of Michigan.
Cooperative Institute for Great Lakes Research, School for Environment and Sustainability, University of Michigan.
Harmful Algae. 2023 Mar;123:102382. doi: 10.1016/j.hal.2023.102382. Epub 2023 Jan 17.
The primary management strategy for minimizing harmful algal blooms (HABs) in Lake Erie has been to reduce springtime loading of phosphorus (P) to the lake. However, some studies have shown that the growth rate and toxin content for the HABs-causing cyanobacterium Microcystis also respond to the availability of dissolved inorganic nitrogen (N). This evidence is based on both observational studies that correlate bloom development with changes in N forms and concentrations in the lake, and experiments in which P and/or N are added at concentrations in excess of those present in the lake. The goal of this study was to determine whether a combined decrease in N and P concentrations from ambient levels in Lake Erie could limit the development of HABs more than a reduction in P concentration only. To directly test the impact of P-only versus dual N and P concentration decreases on phytoplankton in the western basin of Lake Erie, we evaluated changes in growth rate, community composition, and microcystin (MC) concentration through eight bioassay experiments performed from June through October 2018, which encompassed the normal Lake Erie Microcystis-dominated HAB season. Our results showed that during the first five experiments covering June 25 to August 13, the P-only and the dual N and P decrease treatments had similar effects. However, when ambient N became scarce later in the season, the N and P decrease treatments resulted in negative growth rates for cyanobacteria, whereas -P only decreases did not. During low ambient N conditions, dual nutrient decreases lowered the prevalence of cyanobacteria among the total phytoplankton community and decreased microcystin concentrations. The results presented here complement previous experimental work on Lake Erie and suggest that dual nutrient control could be an effective management strategy to decrease microcystin production during the bloom and even possibly diminish or shorten the duration of the bloom based on creating nutrient limiting conditions sooner in the HAB growing season.
减轻伊利湖有害藻类水华（HAB）的主要管理策略一直是减少春季向湖中输入磷（P）。然而，一些研究表明，引起 HAB 的蓝藻微囊藻的生长速度和毒素含量也受到可溶解无机氮（N）的可用性的影响。这一证据基于以下两个方面：一是观察性研究表明，在湖中 N 形态和浓度发生变化时，水华的发展与之相关；二是在实验中，以超过湖中实际存在的浓度添加 P 和/或 N。本研究的目的是确定与仅减少 P 浓度相比，从伊利湖环境水平降低 N 和 P 浓度是否可以更有效地限制 HAB 的发展。为了直接测试 P 单一组分和 N 和 P 双组分浓度降低对伊利湖西部水域浮游植物的影响，我们评估了通过 2018 年 6 月至 10 月进行的 8 项生物测定实验，浮游植物生长率、群落组成和微囊藻毒素（MC）浓度的变化，这些实验涵盖了伊利湖微囊藻为主的 HAB 季节。结果表明，在前五个实验中，6 月 25 日至 8 月 13 日期间，P 单一组分和 N 和 P 双组分降低处理具有相似的效果。然而，当季节后期环境 N 变得稀缺时，N 和 P 降低处理导致蓝藻出现负生长率，而仅 -P 降低处理则不会。在低环境 N 条件下，双营养物降低处理降低了总浮游植物群落中蓝藻的丰度，并降低了微囊藻毒素浓度。本研究结果补充了之前关于伊利湖的实验工作，并表明双营养物控制可能是一种有效的管理策略，可以减少水华期间的微囊藻毒素产生，甚至可能根据在 HAB 生长季节更早地创造营养限制条件来缩短或缩短水华持续时间。
