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

我的研究项目主要集中在过量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形成。我确定了一个关键的驱动因素，解释了如何添加一个关键的营养素，磷（P），淡水导致密集的水华形成。这使加拿大在解决世界各地淡水系统面临的最棘手的环境问题之一方面走在了前列。这一新的信息对于改善防止水华的管理方案至关重要，特别是因为蓝藻水华正变得越来越普遍，即使一些湖泊的营养水平已经下降。 蓝藻水华形成的关键驱动因素是沉积物/水边界缺氧（定义为溶解氧和硝酸盐的完全丧失），导致亚铁释放到上覆水中。这一顺序（沉积物缺氧->亚铁释放->水华）的发现具有重要的管理意义，因为我们现在知道，水华可以通过防止沉积物/水边界溶解氧的完全丧失来防止。这使得管理人员能够设定保护氧气水平的P目标。 支持这一新概念的证据已经从七个深湖中获得，但还需要更多的证据。第一，要求提供资金，在全湖规模进行控制良好的实验，即，概念验证测试，其中沉积物将在遭受蓝藻水华的富营养化湖泊中被氧化，以确定沉积物的氧化是否阻止水华的形成。 第二，我们不知道这种顺序（沉积物缺氧->亚铁释放->水华）是否发生在浅水、混合良好的系统中，如伊利湖的西部盆地，该盆地每年都会发生大规模水华，尽管有理由相信，在浅水、富营养化的湖泊中会发生暂时的沉积物缺氧。我假设气候变化增加了水华的发生频率，这可以解释为什么伊利在20世纪90年代中期，即使营养物质下降，水华也开始再次形成。我建议安装传感器长达6个月，以监测溶解氧和温度沿着湖底在两个大的浅水湖，西部伊利和湖的森林。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泊中缺氧是否会导致水华形成。 第三个项目将继续调查加拿大各地湖泊中的代谢必需微量金属，以填补知识空白，特别是富营养化湖泊。初步证据表明，当氮供应短缺时，某些区域某些富营养湖泊中某些微量金属（钼、铁，可能还有钴）的浓度极低，会限制蓝细菌的生长。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，使它们不适合用于除氮项目。

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.