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

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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.