Variation in ecosystem sensitivity and response to anthropogenic atmospheric inputs, Upper Great Lakes Region

Stottlemyer, J

Variation in ecosystem response to present inputs of atmospheric contaminants, especially acid precipitation in the Upper Great lakes region, is discussed. The value of applying an ecosystem approach in such an assessment is emphasized. The results summarize pertinent parts of the first three years of Lake Superior basin baseline watershed ecosystem studies conducted in Isle Royale National Park, Keweenaw Peninsula, MI and in Pictured Rocks National Lakeshore, MI. Precipitation throughout the Upper Great Lakes region is considered to be acidic. Average annual pH values range from 4.4 in lower Michigan to 5.2 in western Minnesota. In the central portion of the region the comparative values for average annual pH has fallen from 6 to 4.6 since 1955. It appears the regional loading of acidity and associated contaminants is increasing. Isle Royale and basin ecosystem studies show that Lake Superior significantly modifies precipitation inputs temporally and spatially. Since half the annual precipitation is snow, this results in the heaviest load of atmospheric contaminants in the more sensitive low order watersheds. Hardwood canopies seasonally neutralize acid precipitation while boreal canopies have little effect. Glacial till appears to be more important than bedrock composition in determining whether acid precipitation is neutralized by carbonates or basic aluminum salts. The latter case can result in the release of soluble aluminum. The vulnerability of lakes and streams is known to be dependent on the nature and degree of watershed buffering. Watersheds with northern hardwoods generally have extensive glacial till, and this vegetation/soil interaction suggests that such ecosystems are much more resistant to the direct impacs of acid precipitation than are boreal ecosystems.

Variation in ecosystem sensitivity and response to anthropogenic atmospheric inputs, Upper Great Lakes Region

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