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Phosphorus and Excess Algal Growth


Like people, a lake requires many nutrients in proper amounts to stay healthy. In the Great Lakes, phosphorus is the nutrient that has the most influence on the health of lake ecosystems.

Phosphorus is found throughout the lake ecosystem in the open lake, in nearshore areas, in rivers and streams, and on land. It is also found in various other media, such as soils and sediments, plants, and animals.

Phosphorus is contained in common items like detergents, fertilizer, manure, human waste and decaying plants. These can come from many sources, including runoff from agricultural and urban land, airborne particles, septic systems and industrial discharges, and fertilizer. There are also naturally-occurring sources of phosphorus in lakes, such as decaying organic matter, and eroding rocks and soils.

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History of the Phosphorus Issue in the Great Lakes

A closer view of an algal bloom. Photo: Dr. J.M. Reutter, Ohio Sea Grant and Stone Laboratory.

A closer view of a recent algal bloom. Photo: Dr. J.M. Reutter, Ohio Sea Grant and Stone Laboratory.

During the 1960s, water quality issues in the Great Lakes became a public concern. In particular, Lake Erie was perceived to be ‘dying’ because of extensive algal growth that occurred throughout the lake as a result of excessive inputs of phosphorus. This process is called cultural eutrophication.

By the late 1960s, Canada and the United States were in agreement that limiting phosphorus inputs to the Great Lakes, particularly Lake Erie, was key to controlling excessive algal growth, and that a coordinated approach to phosphorus reduction was required.  This understanding and call for action was a primary focus of the 1972 Great Lakes Water Quality Agreement. Because of the coordinated action by Canada and the United States, phosphorus levels in Lake Erie and the other Great Lakes declined during the 1970s and 1980s. This was an unprecedented success in achieving environmental results through binational cooperation.

In the mid-1990s, excessive algal growth began to re-emerge as a problem in the Great Lakes. Phosphorus remains the primary factor influencing excessive algal growth, but the reasons for the resurgence of excessive algal growth are more complex than in past decades.

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When the Phosphorus Balance is Lost

Some areas of the Great Lakes have more phosphorus than they need to be healthy, and intervention is required to reduce phosphorus back to appropriate levels.  When the balance is lost and phosphorus levels are too high, the excess phosphorus contributes to excess algal growth. Certain types of blue-green algae like Microcystis and other species may produce toxins that are harmful to both humans and wildlife. Excess phosphorus also leads to the development of mats of floating or attached algae that form unattractive green tints, slimes or threads and are often quite odorous. When the algae die, the mats sink to the lake bottom and decay, creating low-oxygen conditions that are fatal to fish and some other aquatic organisms.

Dresseinid mussels also contribute to nutrient imbalances in open waters. These include zebra and quagga mussel species, which are aquatic invasive species that are constantly capturing and excreting nutrients in the areas close to the shores of the Great Lakes. This promotes the growth of harmful algae in nearshore areas.

Excess algal growth can impair fish and wildlife habitats, and can interfere with human activities such as swimming, boating and fishing.  For example, some algal toxins have the potential to produce serious human health issues and are therefore of concern for drinking water systems. Industrial, municipal or private infrastructure may also incur additional operating costs to minimize the risks associated with algal toxins. These impacts of algal growth can have serious environmental, economic and social consequences for various industries, including recreational tourism, cottaging, boating, fishing and hunting. Priority attention and action is required to address excessive algal growth due to the serious effects they can have to human health, the environment, the economy and society.

Recently, excess algal blooms have been observed regularly in large areas of Lake Erie, and they have also been observed less often in localized nearshore areas in the other Great Lakes. Lake Erie is the shallowest and most biologically productive of all the Great Lakes, meaning that it is highly sensitive to changes in nutrient levels and changes in the food web. 

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Restoring the Phosphorus Balance

Managing phosphorus levels in lakes is complex, and inputs are only one part of the problem. Once in the lake, phosphorus and nutrients move throughout the system via the food web. The food web includes plants, animals and people as well as the habitats that support them. Along with nutrient sources, the structure of the food web and the organisms within it significantly influence the amount of nutrients available to contribute to excessive algal blooms.

In recent years, the food web has been altered with the arrival of non-native invasive species. Over 180 aquatic non-native species have been either intentionally or accidently introduced into the Great Lakes since 1840. In some cases, these non-native invasive species have contributed to the increase in excessive algal growth in the Great Lakes, despite nutrient source reductions that were achieved in the 1970s. Non-native invasive organisms can take phosphorus and nutrients away from organisms that are native to the Great Lakes, altering the food web and ultimately changing the availability and forms of phosphorus in the ecosystem.

As a result of these ecosystem changes and changes in phosphorus sources, the nutrient management approaches used in the 1970s are no longer adequate.

To keep up with the ever-changing Great Lakes ecosystem of today, nutrient management must constantly adapt.  New nutrient management approaches require research, monitoring and assessment, goal-setting, project implementation, and reporting that are reviewed and revised on a regular basis. By using this cyclical adaptive management model, changes related to phosphorus sources, and the effectiveness of our management actions can be better understood. Nutrient management plans can be more targeted and more effective restoration actions can be identified and implemented.

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Solutions and Actions

What is Environment and Climate Change Canada Doing to Address Phosphorus and Excess Algal Blooms?

Within the Great Lakes basin, Environment and Climate Change Canada recognizes the interconnectedness of these issues and has worked with its partners to address phosphorus and excess algal blooms by using a combination of science, governance and action. Setting objectives for phosphorus loadings to the Great Lakes is key to the success of phosphorus reduction efforts. This work is being done in collaboration with partners at the binational, domestic, provincial and local levels.

Establishing Reduction Targets

In February 2016, Canada and the United States announced new joint phosphorus targets which call for a reduction in the amount of phosphorus entering Lake Erie by forty per cent.  As targets are set, the focus shifts to achieving them, which includes developing a domestic action plan, monitoring and reporting on progress.

Great Lakes Nutrient Initiative

The Great Lakes Nutrient Initiative provides funding to address the complex problems of recurrent toxic and nuisance algae in the Great Lakes, with a focus on Lake Erie.

The Great Lakes Nutrient Initiative advances the science to understand, and policies to address, the complex problem of recurrent toxic and nuisance algae in the Great Lakes. The Initiative focuses on Lake Erie, the smallest and shallowest of the Great Lakes and most susceptible to nearshore water quality issues. The science and policy approaches developed through the Initiative are transferable to the other Great Lakes and bodies of water in Canada.

The Initiative currently focuses on:

  • Conducting scientific monitoring and modeling to measure and report Canadian phosphorus loadings to Lake Erie;
  • Establishing targets for the Eastern Basin of Lake Erie;
  • Identifying key phosphorus hotspots to inform phosphorus load reduction actions in the Thames River watershed;
  • Developing tools and approaches for assessing landscapes and land use practices, including determining the effectiveness of agricultural best management practices;
  • Engaging key stakeholders and the public in the development of the domestic action plan which will include policy options and strategies to meet phosphorous reduction targets;
  • Piloting a binational nearshore assessment and management framework.

The Initiative helps Canada to deliver on key commitments under the recently amended Canada – United States Great Lakes Water Quality Agreement.

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Binational and Federal-Provincial Collaboration

Canada and the United States are working together to address many issues, including phosphorus management, through the Great Lakes Water Quality Agreement (GLWQA), which includes a specific Annex and time-bounded commitments for action on this issue. The GLWQA was first signed in 1972, revised in 1978 and amended by protocol in 1987 and renewed in 2012. It expresses the commitment of Canada and the United States to restore and maintain the chemical, physical and biological integrity of the Great Lakes basin ecosystem, and includes a number of objectives and guidelines to achieve these goals.

The Canada-Ontario Agreement on Great Lakes Water Quality and Ecosystem Health (COA) establishes clear responsibilities between federal and provincial ministries and helps Canada meet its commitments under the GLWQA. The 2014 COA also includes a specific annex and time-bounded commitments for domestic actions on this issue. Canada and Ontario continue their important work to protect and restore the Great Lakes.

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What Can You Do to Help?

Everyone can practice phosphorus reduction activities. Here are some ideas:

  • Compost your food waste instead of using a kitchen food waste disposal garburator. Keeping food out of wastewater treatment plants helps to reduce nutrient loadings into the lakes.
  • Use phosphorus-free and slow release organic fertilizers on your lawn and garden, and use them only when it’s not raining or when rain is not being forecasted.
  • Have your septic system inspected regularly and ensure it is properly used and maintained.

Here are ways that other community leaders and organizations can help:

  • Academics and schools can lead research programs, conduct restoration projects and provide educational programs to improve understanding and appreciation of lake ecosystems.
  • Conservation authorities and watershed-based organizations can design and implement watershed-based phosphorus reduction programs in consultation with local communities. They can provide leadership and guidance for watershed and sub-watershed based projects.
  • Non-government organizations can be environmental leaders by encouraging others through environmental and communication programs, research and monitoring, restoration projects and the preservation of environmentally-sensitive areas such as streams, rivers and coastal wetlands.
  • Community groups can take on-the-ground action and raise local awareness about the importance of living sustainably in the Great Lakes basin.
  • Industry, business, farmers, developers and landowners can lead their peers by demonstrating strong environmental values and adopting beneficial (best) management practices that lessen their impacts on lake ecosystems.

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Remaining Challenges

Even after excess algal blooms have been addressed, continuous monitoring and adaptive management of phosphorus inputs will be vital to the future health of the ever-changing Great Lakes ecosystem. Climate change is lengthening the algal growing season, while decreased snowfall and increased rainfall are increasing the size and frequency of phosphorus inputs that run off into the lakes. In Southern Ontario, especially in the Lake Erie and Lake Ontario watersheds, a growing population coupled with intense urban and rural development is likely to increase phosphorus inputs to the lakes.

Taking action to reduce excess algal blooms and adaptively manage phosphorus in the Great Lakes is a key step towards improving and sustaining better water quality for all Canadians for generations to come.

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