Cyanobacterial harmful algal blooms are one of the most prominent threats to water quality in freshwater ecosystems and are expected to become more common as the climate continues to change. While traditional strategies to manage algal blooms have focused on controlling nutrients, manipulating light as a way to reduce cyanobacteria is less frequently explored. Here, we propose the addition of glacial rock flour (GRF), a fine particulate that floats on the water’s surface and remains suspended in the water column, to reduce light availability and in turn, phytoplankton biomass dominated by cyanobacteria. To determine if a sustained reduction in light could lower cyanobacteria biomass and microcystin concentrations, we applied GRF to large-scale (11 kL) mesocosm tanks for 9 consecutive days. Mesocosm tanks were amended by adding nitrogen and phosphorus to generate chlorophyte- and cyanophyte- dominated experimental tanks. To assess how the phytoplankton community was impacted in each tank, we measured photosynthetic irradiance parameters, the maximum quantum yield of photosystem II, gross primary productivity (GPP), phytoplankton biovolume, and phytoplankton community composition before and after the addition of GRF. GRF effectively reduced cyanophyte biovolume by 78% in the cyanophyte-dominated tanks, despite no significant change in total phytoplankton community biovolume. Cyanophytes were replaced by cryptophytes, which increased by 106% in the chlorophyte-dominated tanks and by 240% in the cyanophyte-dominated tanks. The change in photosynthetic irradiance parameters and GPP after the addition of GRF was not significantly different between any of the treatment or control groups, suggesting that either the cyanophytes will likely recover if light availability increases, or that the new cryptophyte-dominated community was well suited to a reduced light environment. Cyanobacterial blooms are expected to increase in frequency and magnitude as climate change progresses, but our study suggests that light manipulation may be a useful in-lake management strategy for controlling these blooms and warrants further investigation.

中文翻译：

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浮游植物群落对光照变化的反应：冰川岩粉可以用来控制蓝藻开花吗？

蓝藻有害藻华是淡水生态系统水质最突出的威胁之一，随着气候的持续变化，预计会变得更加普遍。虽然管理藻华的传统策略侧重于控制养分，但很少有人探索将光作为减少蓝藻的方法。在这里，我们建议添加冰川岩粉 (GRF)，这是一种漂浮在水面上并保持悬浮在水柱中的细颗粒，以减少光照，进而减少以蓝藻为主的浮游植物生物量。为了确定持续减少光照是否会降低蓝藻生物量和微囊藻毒素浓度，我们连续 9 天将 GRF 应用于大型（11 kL）中胚层水箱。通过添加氮和磷来修改中观水箱，以生成以叶绿素和蓝藻为主的实验水箱。为了评估每个水池中浮游植物群落如何受到影响，我们测量了光合辐照度参数、光系统 II 的最大量子产量、总初级生产力 (GPP)、浮游植物生物量和添加 GRF 前后的浮游植物群落组成。尽管总浮游植物群落生物量没有显着变化，但 GRF 在以蓝藻为主的水池中有效地减少了 78% 的蓝藻生物量。蓝藻被隐生植物所取代，在以叶绿素为主的缸中增加了 106%，在以蓝藻为主的缸中增加了 240%。添加 GRF 后光合辐照度参数和 GPP 的变化在任何处理组或对照组之间都没有显着差异，这表明如果光照增加，蓝藻可能会恢复，或者新的隐生植物占优势的群落非常适合到弱光环境。随着气候变化的进展，蓝藻水华的频率和规模预计会增加，但我们的研究表明，光操纵可能是控制这些水华的有用的湖内管理策略，值得进一步调查。