Dependence of cyanobacteria bloom formation and maintenance on anoxia and trace metals in eutrophic lakes

富营养化湖泊中蓝藻水华的形成和维持对缺氧和微量金属的依赖性

• 批准号: RGPIN-2019-06333
• 负责人: Molot, Lewis
• 金额: $ 2.04万
• 依托单位: York University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=753380
• 关键词: Dependence; cyanobacteria; bloom; formation; maintenance

My research program has focused on the impacts of excessive plant nutrients on freshwaters, specifically on the formation of dense blooms of toxic, algae-like cyanobacteria. I identified a key driver that explains how adding a key nutrient, phosphorus (P), to freshwaters causes dense blooms to form. This has put Canada in the forefront of solving one of the most vexing environmental problems facing freshwater systems around the world. This new information is critical to improving management programs that prevent blooms, especially since cyanobacteria blooms are becoming more common even as nutrient levels have declined in some lakes.      The key driver of cyanobacteria bloom formation is the onset of anoxia (defined as complete loss of dissolved oxygen and nitrate) at the sediment/water boundary which results in release of ferrous iron into overlying water. The discovery of this sequence (sediment anoxia ->ferrous Fe release -> bloom) has important management implications because we now know that blooms can be prevented by preventing complete loss of dissolved oxygen at the sediment/water boundary. This allows managers to set P targets that protect oxygen levels.      Evidence in support of this new concept has been obtained from seven deep lakes but additional evidence is needed. First, funds are requested to conduct a well-controlled experiment at the whole-lake scale, i.e., `proof of concept' testing, in which sediments will be oxidized throughout a eutrophic lake that suffers from cyanobacteria blooms to determine if oxidation of sediments prevents blooms from forming.      Second, we do not know if this sequence (sediment anoxia ->ferrous Fe release -> bloom) occurs in shallow, well mixed systems like the western basin of Lake Erie which suffers massive blooms every year although there is reason to believe that temporary episodes of sediment anoxia occur in shallow, eutrophic lakes. I hypothesize that climate change has increased the frequency which would explain why blooms started forming again in Erie in the mid-1990s even as nutrients declined. I propose installing sensors for up to 6 months to monitor dissolved oxygen and temperature along lake bottoms in two large shallow lakes, western Erie and Lake of the Woods. These data will be coupled to data collected from other programs to see if anoxia precedes bloom formation in well mixed, shallow lakes.      A third project will continue a survey of metabolically essential trace metals in lakes across Canada to fill in knowledge gaps, especially eutrophic lakes. Preliminary evidence indicates that very low concentrations of certain trace metals (molybdenum, iron and possibly cobalt) can limit growth of cyanobacteria in some eutrophic lakes in some regions when nitrogen is in short supply. However, I suspect that metal levels are never low enough for this to happen in lakes in high urbanized, industrialized watersheds like Erie, making them unsuitable candidates for N removal programs.

我的研究计划集中在过量的植物营养对淡水的影响，特别是对有毒、藻类蓝藻密集繁殖的影响。我确定了一个关键驱动因素，它解释了向淡水中添加关键营养物质磷(P)是如何导致密集水华的形成的。这使加拿大走在了解决世界各地淡水系统面临的最令人烦恼的环境问题的前列。这些新信息对于改善防止水华的管理计划至关重要，特别是在蓝藻水华变得越来越常见的情况下，尽管一些湖泊的营养水平有所下降。他说，蓝藻水华形成的关键驱动因素是沉积物/水边界的缺氧(定义为完全丧失溶解氧和硝酸盐)，导致亚铁释放到上覆水中。这一序列(沉积物缺氧--亚铁的释放--水华)的发现具有重要的管理意义，因为我们现在知道，可以通过防止沉积物/水边界的溶解氧完全丧失来防止水华的发生。这使得管理者可以设定保护氧气水平的P目标。目前已经从七个深湖中获得了支持这一新概念的最新证据，但还需要更多的证据。首先，需要资金在全湖范围内进行一项受控良好的实验，即“概念验证”测试，在整个经历蓝藻水华的富营养化湖泊中，沉积物将被氧化，以确定沉积物的氧化是否能防止水华的形成。第二，我们不知道这种序列(沉积物缺氧-&gt；亚铁释放-&gt；水华)是否发生在浅层、混合良好的系统中，如每年遭受大规模水华的伊利湖西部盆地，尽管有理由相信，沉积物缺氧的暂时性事件可能发生在浅层、富营养化的湖泊中。我假设，气候变化增加了频率，这可以解释为什么在20世纪90年代中期，即使营养物质减少，伊利也开始再次开花。我建议在伊利湖西部和伍兹湖两个大型浅水湖的湖底安装长达6个月的传感器，监测湖底的溶解氧和温度。这些数据将与从其他项目收集的数据相结合，以确定在混合良好的浅水湖中，缺氧是否先于水华的形成。他说，第三个项目将继续对加拿大各地湖泊中代谢必需的痕量金属进行调查，以填补知识空白，特别是富营养化湖泊。初步证据表明，在氮供应不足的情况下，某些微量金属(钼、铁，可能还有钴)的浓度非常低，会限制某些地区一些富营养化湖泊中蓝藻的生长。然而，我怀疑，在像伊利这样高度城市化、工业化的流域的湖泊中，金属含量永远不会低到足以发生这种情况，这使得它们不适合进行氮去除计划。