Laboratory of Ecology and Physiology of Phytoplankton, Department of Plant Biology, University of Rio de Janeiro State, Rio de Janeiro, RJ, Brazil.
Laboratory of Ecology and Physiology of Phytoplankton, Department of Plant Biology, University of Rio de Janeiro State, Rio de Janeiro, RJ, Brazil.
Harmful Algae. 2022 Aug;117:102262. doi: 10.1016/j.hal.2022.102262. Epub 2022 Jun 6.
One of the main symptoms of eutrophication is the proliferation of phytoplankton biomass, including nuisance cyanobacteria. Reduction of the external nutrient load is essential to control eutrophication, and in-lake interventions are suggested for mitigating cyanobacterial blooms to accelerate ecosystem recovery. Floc & Sink (F&S) is one such intervention technique that consists of applying a low dose of coagulants in combination with ballasts for removing cyanobacteria biomass. It is especially suitable for deep lakes with an external nutrient load that is higher than the internal load and suffers from perennial cyanobacterial bloom events. Studies showing the efficacy of the F&S technique have been published, but those testing its variation in efficacy with changes in the environmental conditions are still scarce. Therefore, we evaluated the efficiency of the F&S technique to remove cyanobacteria from water samples collected monthly from two different sites in a deep tropical reservoir (Funil Reservoir, Brazil) in the laboratory. We tested the efficacy of two coagulants, chitosan (CHI) and poly-aluminum chloride (PAC), alone and in combination with lanthanum-modified bentonite (LMB) in settling phytoplankton biomass. We hypothesized that: ⅰ) the combined treatments are more effective in removing the algal biomass and ⅱ) the efficiency of F&S treatments varies spatially and monthly due to changes in environmental conditions. The combined treatments (PAC + LMB or CHI + LMB) removed up to seven times more biomass than single treatments (PAC, CHI, or LMB). Only the treatments CHI and LMB + CHI differed in efficiency between the sites, although all treatments showed significant variation in efficiency over the months at both the sampling sites. The combined treatments exhibited lower removal efficacy during the warm-rainy months (October-March) than during the mild-cold dry months (April-September). At high pH (pH > 10), the efficiency of the CHI and LMB + CHI treatments decreased. CHI had lower removal efficiency when single-cell cyanobacteria were abundant, while the combined treatments were equally efficient regardless of the morphology of the cyanobacteria. Hence, the combination of PAC as a coagulant with a ballast LMB is the most effective technique to precipitate cyanobacteria under the conditions that are encountered around the year in this tropical reservoir.
富营养化的一个主要症状是浮游植物生物量的增殖，包括有害的蓝藻。减少外部营养负荷对于控制富营养化至关重要，并且建议在湖泊内进行干预以减轻蓝藻水华，从而加速生态系统恢复。絮凝沉降（F&S）就是这样一种干预技术，它包括投加低剂量的混凝剂并结合加重剂来去除蓝藻生物量。该技术特别适用于外部营养负荷高于内部负荷且常年发生蓝藻水华的深湖。已经发表了表明 F&S 技术有效性的研究，但仍缺乏测试其在环境条件变化时功效变化的研究。因此，我们在实验室中评估了 F&S 技术从巴西深热带水库（芬尼尔水库）两个不同地点每月采集的水样中去除蓝藻的效率。我们测试了两种混凝剂壳聚糖（CHI）和聚合氯化铝（PAC）单独以及与镧改性膨润土（LMB）结合使用对浮游植物生物量的沉降效果。我们假设：i）联合处理在去除藻类生物量方面更有效，ii）由于环境条件的变化，F&S 处理的效率在空间和每月上有所不同。联合处理（PAC + LMB 或 CHI + LMB）去除的生物量比单独处理（PAC、CHI 或 LMB）多七倍。只有 CHI 和 LMB + CHI 处理在两个地点之间的效率上有所不同，尽管所有处理在两个采样地点的各个月份都表现出显著的效率变化。在温暖多雨的月份（10 月至 3 月），联合处理的去除效率低于温和寒冷干燥的月份（4 月至 9 月）。在高 pH 值（pH > 10）时，CHI 和 LMB + CHI 处理的效率降低。当单细胞蓝藻丰富时，CHI 的去除效率较低，而联合处理无论蓝藻的形态如何都具有相同的效率。因此，在该热带水库全年遇到的条件下，PAC 作为混凝剂与加重剂 LMB 的组合是沉淀蓝藻最有效的技术。
