Issue 61
January 19, 2006

EnviroZine: Environmnent Canada's On-line Newsmagazine

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Great Lakes – St. Lawrence Basin:
A Freshwater Giant

Ontario Lake near the Niagara River. Photo: Magella Pelletier.

From the heartland of North America, freshwater travels 3000 kilometres through the Great Lakes, the St. Lawrence River, and into the Gulf of St. Lawrence. Taken all together as a single unit, this is the Great Lakes – St. Lawrence basin, a unified ecosystem and a true marvel of nature. Its complexity of functions creates a delicate balance which scientists are only just beginning to understand.

The Great Lakes – St. Lawrence water system is one of the world's largest. Approximately 15 million Canadians and 30 million Americans call the basin home. With so many people and so much economic activity in the basin it is little wonder that it has come under threat from industrial, municipal, and agricultural pollution, invasive species, toxic contaminants and loss of biodiversity.

Although our footprint is often local, the impacts can reverberate throughout the ecosystem. The loss of a species, a farm's contaminated run-off, a city's untreated sewage, the introduction of an invasive species, or a stretch of eroded shoreline are all serious problems individually. Taken together, their cumulative environmental impact on the basin represents a considerable threat to the ecosystem's health.

Going with the Flow

Map of the Great Lakes and St. Lawrence River. Click to enlarge.

The Great Lakes – St. Lawrence basin contains about a quarter of the Earth's freshwater reserves. What happens here impacts the environmental processes of the entire North American continent. Still, pollution concerns are too often focussed on local activities, with each part of the ecosystem managed in isolation. Historically there has been little consideration of how activities in one part of the ecosystem may impact another. This separation obscures the full picture of the basin's health, especially since roughly 40 per cent of pollution in the St. Lawrence originates upstream in the Great Lakes.

The Great Lakes and its connecting channels are like steps descending from Lake Superior at 183 metres above sea level to the Atlantic Ocean. Lake Ontario, the last stage before the St. Lawrence River, sits at about 74.7 metres.

Water from Lake Superior flows into Lake Huron via St. Marys River. The broad and deep Straits of Mackinac link Lakes Michigan and Huron, which flow through the St. Clair River, Lake St. Clair and the Detroit River before emptying into Lake Erie. The water travels from here through the Niagara River and the Welland Canal into Lake Ontario before flowing to the Atlantic Ocean through the St. Lawrence River.

The Great Lakes and the St. Lawrence River form a single hydrological system and any changes will also be felt downstream. The water levels and flows are influenced by many factors and variations are normal. However, extreme and prolonged shifts, such as climate change and human interventions like dam building and man-made islands, cause dramatic and permanent changes to level and flow in the entire ecosystem, upsetting the delicate equilibrium in the process.

The Ecosystem Approach

Fast Facts:

The Great Lakes – St. Lawrence basin contains about a quarter of the Earth's freshwater reserves.

The Great Lakes and its connecting channels are like steps descending from Lake Superior at 183 metres above sea level to the Atlantic Ocean.

Mercury concentrations in sediments of the Great Lakes – St. Lawrence system have declined by approximately 50 per cent in the past 30 years.

Studies show a tremendous increase in the number of breeding cormorants in the last 30 years.

Approximately two-thirds of the Lower Great Lakes and St. Lawrence River wetlands have been lost over the past four centuries.

Related Sites

Great Lakes – St. Lawrence Ecosystem

St. Lawrence Centre

Freshwater Web Site

Related EnviroZine Articles

Protecting and Restoring the Great Lakes

Double-crested Cormorant distribution map. Click to enlarge.

Efforts are now being taken to study this ecosystem as a whole. The ecosystem approach is generating new insights into the environmental integrity of the basin and recognizes the importance of monitoring the state of health in the Great Lakes – St. Lawrence basin, as well as trends, causes and effects. Some of these efforts are reflected in a set of recently released facts sheets from Environment Canada, which look at the health of aquatic birds, water quality and toxic contamination, mercury contamination of sediment and area wetlands.

Double-crested Cormorant - Photo: John Mitchell

Bird monitoring is now taking into consideration both Great Lakes and St. Lawrence populations. For instance, studies show a tremendous increase in the number of breeding cormorants in the last 30 years. In the early 1970s, there were fewer than 150 nesting pairs in the entire Great Lakes; by 2000, an estimated 115 000 pairs were nesting on approximately 250 colonies in the Great Lakes region. In the St. Lawrence River the Double-crested Cormorant lives mainly in the estuary and the Gulf, where its population is presently estimated at 24 000 nesting pairs distributed in approximately 80 colonies.

Monitoring of water quality has shown that pesticides often originate upstream from where they are found. Similar concentrations of pesticides have been discovered at the inlet and outlet of Lake Ontario as well as the St. Lawrence River. These pesticides likely came from farmlands near Lake Ontario. That said, monitoring has shown that the water quality has significantly improved, with the most serious contaminants staying within water quality guidelines.

Mercury concentrations in sediments of the Great Lakes – St. Lawrence system have declined by approximately 50 per cent in the past 30 years. Regulatory measures both in the US and Canada have successfully improved industrial processes and water cleanup. Nonetheless, challenges like the long distance travel of airborne mercury remain.

Wetland - Photo: Martin Jean. Click to enlarge.

The wetlands along the Great Lakes – St. Lawrence help to control erosion and regulate floods. They are wildlife nurseries and nesting sites, feeding grounds and resting places, water filters and reservoirs. They help protect shoreline areas from storm damage and attract fish, birds, amphibians, reptiles and mammals. Unfortunately, with approximately two-thirds of the Lower Great Lakes and St. Lawrence River wetlands lost over the past four centuries, the functions and values of wetlands are still not widely recognized. In some areas of the basin, this destruction has reached 80 per cent. Wetlands located along urban shoreline areas are especially at risk due to high development pressure and stresses such as regulation of water levels.

By recognizing the interconnectedness within the Great Lakes – St. Lawrence ecosystem and jointly monitoring changes in several indicators at once, scientists are starting to understand the evolution of the ecosystem as a whole. Already, in the past few years, scientists have learned how to characterize the sources of pollutants, estimate their concentrations, and examine how they change over time. And their use of the ecosystem approach is making it easier to develop effective strategies for restoring and protecting the basin.

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Issue 61 January 19, 2006

Great Lakes – St. Lawrence Basin: A Freshwater Giant

Going with the Flow

The Ecosystem Approach

Issue 61
January 19, 2006

Great Lakes – St. Lawrence Basin:
A Freshwater Giant