Bridget McGlynn is a Master of Sustainability candidate in the Environmental Sustainability Research Centre at Brock University interested in socialecological systems and water sustainability. Before attending Brock, she completed McMaster University’s Integrated Science program where she researched algal blooms in Lake Erie and learned the importance of interdisciplinary research and recognizing how systems are interconnected.

“The Great Lakes are an amazing resource for Canadians; they provide freshwater, wildlife habitat, economic opportunities, and recreational activities. Growing up on the shores of Lake Ontario, I was aware of some of the issues facing the lakes, such as pollution and invasive species, from a young age. However, learning about the drinking water emergency that occurred in Toledo in 2014 provided me with a clear, contextual link of how water quality in the Great Lakes impacts public health in the region. Uncontrolled algal blooms in Lake Erie pose a public health threat and climate change will exacerbate this issue. Outlining steps to mitigate algal blooms will help protect Lake Erie water quality and serve as an example of executional climate change adaptation to a broader audience.”

Lake Erie provides more than 11 million people with freshwater and generates nearly $50 million in economic activity through shipping, fisheries, and tourism [1]; however, the modern, yearly late summer blue-green algae (cyanobacteria) blooms in the Western Basin of Lake Erie present a severe risk to ecosystem services, economic outputs, and public health [2].

By the 1960s and 70s, nutrient pollution of phosphorous and nitrogen resulted in severe algal blooms dominated by green algae. The implementation of the action plan outlined in the 1972 Great Lakes Water Quality Agreement (GLWQA) resulted in the significant decline of phosphorous pollution from point sources, such as wastewater treatment plants [3]. The guidelines of the GLWQA primarily focused on phosphorous as the limiting nutrient for algal growth and thereby the main target for mitigation strategies. This reduction in phosphorous led to a reduction of algal blooms by the early 1990s [4,5]. However, by the mid-1990s, the algal booms returned to Lake Erie. Modern Lake Erie algal blooms consist primarily of the cyanobacteria genus Microcystis. Previous green algae blooms would alter ecological services and recreational opportunities but did not impact human health. However, Microcystis blooms create a public health hazard through the production of microcystin, a liver toxin. In 2014, 500 000 residents of Toledo, Ohio experienced a ‘do not drink, do not boil’ water advisory due to harmful microcystin levels in tap water.

While limiting phosphorous pollution was a primary means of controlling green algae blooms in the 1970s, phosphorous appears to be only one of multiple factors influencing the cyanobacteria blooms in Lake Erie since the mid-2000s, as phosphorous levels are below that of 1972 but blooms are exceeding the records set 40 years prior [6].

Research has demonstrated the modern Microcystis blooms are co-limited by phosphorous and nitrogen [2,7,8]. Experiments have additionally displayed insufficient nitrogen concentrations result in the downregulation of all microcystin toxin-producing genes in Microcystis that resulted in toxin concentrations below detectable levels in all samples [9]. This suggests further nitrogen limitations would reduce environmental nitrogen concentrations to levels that would impede not only growth but also toxin product ion. However, the understanding of the impact of nitrogen pollution is relatively recent and has not yet been reflected in policy, even though sampled Microcystis populations from other bodies of water have also displayed nitrogen limitation [10,11].

A recent assessment has forecasted that uncontrolled algal blooms could cost Canada $5.3 billion over the next 30 years [12]. As excessive microcystin concentration in lake water has already created a public health emergency in Toledo in 2014, future algal blooms may pose similar risks [13]. As climate change will likely result in larger and more severe algal blooms, immediate action is required to protect Lake Erie water quality.

The following are proposed actions to expand the scope of the nutrient removal efforts to successfully minimize the severity of modern algal blooms.

1. Recognition of Nitrogen in the GLWQA

Phosphorus was the main target for nutrient reduction strategies for decades, both in Lake Erie and around the world, as previous sentiments expressed that reducing nitrogen pollution would be an ineffective method of mitigation [14]. A focus on reducing phosphorous pollution worked as a mitigation strategy in the 1970s and 1980s, and while this same focus was transferred to the proposed mitigation strategies for modern blooms, they have proved insufficient in controlling bloom size and toxicity. Despite phosphorous levels below that of the 1970s, blooms are significantly larger [6]. As nitrogen influences microcystin production and Lake Erie bloom extent, the recognition of nitrogen as a limiting nutrient is essential for future successful mitigation policies. The role of nitrogen needs to be cited in Annex 4 of the GLWQA by the International Joint Commission (IJC). Without this preliminary step, the following mitigation measures may not be as effective for securing funds for implementation.

2. Urea reduction through fertilizer best practices

Microcystis’ preferences for specific nitrogen species suggest pollution reduction strategies should be targeted. Microcystis’ ability to selectively use urea as a sole nitrogen source suggests a reduction of environmental urea concentrations may impede the development of cyanobacteria blooms in Lake Erie [9]. Therefore, reduction of urea concentrations should be a target in algal bloom mitigation strategies. Reduction of urea pollution can occur via the implementation of best practices in urea fertilizer usage in the Maumee watershed. The Maumee watershed passes through northeastern Indiana into northwestern Ohio and is a major contributor of nutrient pollution as it passes through well-fertilized farmland and urban centres [8]. Since urea now represents over 50% of nitrogen sources in fertilizer and about 15% of bioavailable nitrogen in surface waters, urea represents a significant species in nitrogen enrichment [15,16]. The implementation of best management practices could reduce the fertilizer carried away in runoff. Best management practices for fertilizer usage needs to follow the four Rs: Right product, right rate, right time, and right place [2]. Ideally, the best management practices would optimize fertilizer uptake and minimize environmental losses [17]. The implementation of best practices would decrease the concentration of urea entering local waterways due to run off.

3. Wetland Restoration

The restoration of wetlands would reduce the urea load that eventually enters the Western Basin of Lake Erie. Approximately 95% of wetlands around the Western Basin of Lake Erie have been lost [18]. Wetlands have been demonstrated to absorb and transform various nitrogen and phosphorus species thereby removing it from the water column [19]. Marshes can remove suspended solids, particulate bound nutrients, and excessive algal growth from the connected lake [20]. Approximately 2-7% of the Maumee watershed would need to be converted to a form of wetland to make a significant reduction in nutrient loading [21]. Wetland restoration has been completed in other eutrophic basins to reduce nutrient loadings and subsequently algal bloom severity. The Kis (small)-Balaton Water Protection System (KBWPS) was constructed at the mouth of the main nutrient loading tributary of Lake Balaton, Hungary. The KBWPS, a wetland reconstruction, retains two-thirds of the phosphate and over half of the nitrate in the incoming water [22]. The overall result was an increase in the water quality of Lake Balaton’s previously hypereutrophic basin [22]. Partial restoration of the Great Black Swamp, the wetland region that previously encompassed the western shore of Lake Erie, could produce comparable results.