The state of knowledge about harmful algal blooms of cyanobacteria in the Great Lakes

Cyanobacteria bloom in July 2020 on Wenona Beach on Saginaw Bay, Lake Huron.(As part of Lakes Appreciation Month, MI Environment features a story about harmful algal blooms by Michelle Selzer, lake coordinator at the Great Lakes State’s Michigan Department of Environment, Great Lakes and Energy’s Water Resource Division. report

Harmful algal blooms (HABs) of cyanobacteria in freshwater systems such as the Great Lakes pose a growing threat to human and environmental health. The term HAB generally describes accumulations of cyanobacteria in amounts that are aesthetically unappealing and capable of producing algal toxins. While not all cyanobacteria produce toxins, significant blooms can still pose risks to human and ecosystem health.

Cyanobacteria, which live in both freshwater and saltwater environments, are among the oldest life forms on Earth. Since the mid-1990s, some water bodies in the Great Lakes basin have experienced an increase in the size, duration, and frequency of toxic cyanobacterial HABs. In the case of the western basins of Lake Erie and Green Bay in Lake Michigan, these flowers can last all summer. Outside of these well-known locations, HABs occur in other areas, including Saginaw Bay and Georgian Bay (Canada) in Lake Huron; Sodus Bay (New York) and Quinte Bay (Canada) in Lake Ontario; the Canadian side of Lake St. Clair in the St. Clair Detroit River System; and in Thunder Bay (Canada) and near the Apostle Islands (Wisconsin) in Lake Superior. HABs are unfortunately also common phenomena in many inland lakes and ponds, especially those with developed shorelines and watersheds.

The presence of cyanobacterial blooms in Lake Superior in recent years has been a surprising development because the lake is a cold, nutrient-poor Great Lake, compared to the other lakes where HABs are common. These conditions are considered limiting for cyanobacteria. Research at Lake Superior points to the role of severe storms in causing flooded rivers to deliver unusually high pulses of nutrients to the lake. Rivers can also play a vital role in “strewn” areas of the lake with cyanobacteria that can bloom under the right conditions. Research is underway to better understand the conditions that may facilitate the development of these unusual flowers in Lake Superior, including changes in light penetration, temperature variations, shifts in nutrient concentrations, and dynamic internal and external sources of nutrient loading to the lake.

The causes of HAB events in the Great Lakes basin are complex and may or may not be synergistic, depending on factors such as the trophic state (ie amount of biological productivity) of the lake. Known causes of cyanobacterial HABs in the Great Lakes include changes in agricultural management practices in the watersheds, extreme weather events in spring, and drought in summer. Increased air temperatures warm the lakes, especially in the shallow coastal areas, and can cause reduced ice cover in the winter months. The invasion of zebra and quagga mussels has led to the capture of nutrients closer to shore. These nearshore areas are also often prone to significant wave action and sediment build-up, which can release accumulated nutrients from the sediment and further encourage algae growth.

The Great Lakes scientific community expects climate change to increase air and water temperatures and alter precipitation patterns, leading to more frequent extreme weather events in the Great Lakes region. This can lead to more intense and widespread cyanobacterial HABs, although warmer winters can also produce less snow and reduce the amount of nutrients carried by rivers during spring snow melt. The interaction of these complex environmental factors and the importance of increased nutrient availability remain areas of valuable research, especially under increasingly unpredictable future climate scenarios. In addition to climate change factors, Great Lakes fisheries managers are also beginning to investigate the long-term biological effects of mussels on coastal eutrophication and the supply of nutrients at sea that support the food web and primary fishery productivity in the Great Lakes .

While the understanding of cyanobacterial HABs has increased significantly in recent years, additional ecological research and comprehensive environmental monitoring technologies are needed at various spatial and temporal scales to further enhance the understanding of the impacts of climate change and the role of internal and external nutrient sources fueling HAB events. improve in the Great Lakes. Expanding ecological forecasting, monitoring and modeling for HABs across the lakes will also be critical to improve predictions of when and where HABs may occur, including their duration, severity and toxicity.

As our knowledge improves, this information can be used to inform binational, federal, state, and local resource management decision-making to address controllable nutrient resources and better inform the public about risks associated with HABs. Managers take a more holistic and adaptive approach designed to integrate new research and lessons learned about the effects of previous management actions. This will be key in our Great Lakes community’s ability to restore both the short- and long-term ecosystem health of the Great Lakes region and protect it from future HAB events in places like Lake Superior.

caption: Cyanobacteria bloom in July 2020 on Wenona Beach on Saginaw Bay, Lake Huron.

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