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

我的研究项目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形成密集繁殖的影响。我发现了一个关键的驱动因素，解释了向淡水中添加一种关键的营养物质——磷(P)是如何导致密集藻华形成的。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。这一新信息对于改善防止藻华的管理程序至关重要，尤其是在一些湖泊的营养水平下降的情况下，蓝藻华正变得越来越普遍。蓝藻华形成的关键驱动因素是在沉积物/水边界缺氧（定义为溶解氧和硝酸盐的完全损失）的开始，导致亚铁铁释放到上覆的水中。这个序列的发现（沉积物缺氧->亚铁铁释放->水华）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/水边界溶解氧的完全损失来防止水华。这使得管理人员可以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。首先，要求资金在全湖范围内进行控制良好的实验，即“概念验证”测试，在该测试中，沉积物将在整个遭受蓝藻繁殖的富营养化湖泊中被氧化，以确定沉积物的氧化是否会阻止藻华的形成。其次，我们不知道这个序列（沉积物缺氧->亚铁铁释放->水华）是否发生在浅层混合良好的系统中，比如伊利湖西部盆地，每年都会发生大规模的水华，尽管有理由相信，沉积物缺氧的临时发作发生在浅层富营养化湖泊中。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，伊利也开始再次形成水华。我建议在伊利湖西部和伍兹湖这两个大浅湖的湖底安装传感器，监测溶解氧和温度，时间长达6个月。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湖中，缺氧是否先于水华形成。第三个项目将继续调查加拿大各地湖泊中代谢必需的微量金属，以填补知识空白，特别是富营养化湖泊。初步证据表明，当氮供应不足时，某些微量金属（钼、铁和可能的钴）的极低浓度会限制某些富营养化湖泊中蓝藻的生长。然而，我怀疑，在伊利湖这样高度城市化、工业化的流域，金属含量从来没有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。

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.