Great Lakes Literacy, Principle One – bodies of fresh water connected to each other and to the world
Great Lakes Literacy is an understanding of the Great Lakes’ influence on you and your influence on the Great Lakes. Principle One focuses on Great Lakes connections.
February 20, 2012 - Author: Steve Stewart, Michigan State University Extension
This article is the second in a series of articles discussing what Great Lakes literacy means for residents of the state of Michigan and the Great Lakes region.
The Great Lakes are a dominant physical feature of North American and form part of the political boundary between the United States and Canada. The Great Lakes system includes five Great Lakes – Superior, Michigan, Huron, Erie and Ontario (easily remembered using the HOMES acronym) – and the connecting channels that include the St. Marys, St. Clair and Detroit Rivers, Straits of Macinac and Lake St. Clair. Each lake has distinctive basin features, circulation and ecology.
The Great Lakes contain approximately 20% of the world’s surface fresh water and have a coastline longer than the nation’s East Coast. Approximately 95% of North Americas’ surface fresh water is in the Great Lakes.
The Great Lakes, their watershed and waterways, and the ocean are all connected. Within the Great Lakes system, water flows from the upper lakes – Superior is approximately 600 feet above sea level, with Michigan and Huron hydrologically linked at the Straits of Mackinac and sharing an elevation of approximately 578 feet – down through Lake St. Clair into Lake Erie, over Niagara Falls, into Lake Ontario, and through the St. Lawrence River into the ocean. Lake level is the height of the Great Lakes relative to sea level. Lake level changes are caused by variations in precipitation, evaporation, runoff, wind and waves. While tides are typically not discernible in the Great Lakes, seiches – a type of standing wave – are common.
The Great Lakes are an integral part of the water cycle and are connected to the region’s watersheds. Changes in water systems affect the quality, quantity and movement of water, including retention time. Rivers and streams transport nutrients, dissolved gasses, salts and minerals, sediment and pollutants from watersheds into the Great Lakes.
Water currents circulate within the Great Lakes and are powered by wind, waves, energy from the sun and water density differences. The shape of a lakebed and its geographic orientation, the direction of the prevailing winds, the shore and the structures along the shore influence the path of water circulation. Circulation between lakes is driven by gravity.
Regions of the Great Lakes stratify in the summer and winter, forming distinct layers based on water temperature differences. Turnover can occur in the spring and fall when cooler weather minimizes temperature differences and the layers mix. Turnover is the main way that oxygen and nutrient-poor water in the deeper areas of the lakes can be mixed with oxygen and nutrient-rich surface water.
Although the Great Lakes are very large, all who live within the Great Lakes basin need to remember that they are finite, their resources are limited and we share a common responsibility for being good stewards of these Freshwater Seas. MSU Extension offers many opportunities to learn more about the Great Lakes, such as the Great Lakes Education Program, Summer Discovery Cruises, and 4-H Great Lakes & Natural Resources Camp. Get involved today!
This article was adapted from Great Lakes Literacy: Essential Principles and Fundamental Concepts for Great Lakes Learning (Ohio Sea Grant, 2010).