W. Keller

Effects of emission reductions from the Sudbury smelters on the recovery of acid- and metal-damaged lakes

Aquatic ecosystems in a 17,000 km2 area around Sudbury, Ontario, Canada, have been affected by the atmospheric deposition of pollutants from nearly a century of operations at the Sudbury area metal smelters. Effects were most severe in the lakes closest to the smelters which historically received very high deposition of both acid and metal particulates. After smelter emissions were greatly reduced in the 1970‘s, evidence began to emerge of improvements in lake water quality, and some recovery of biological communities, and the emphasis of Sudbury area monitoring programs changed from the assessment of damage to the tracking of recovery patterns. Further reductions in smelter emissions during the1990‘s have been accompanied by continuing improvements in aquatic habitat quality, but the evaluation of lake responses to emission controls is complicated by the interaction of lake acidity and metal concentrations with other factors. Weather-related variations in storage and release of sulphur from lake catchments appear to greatly influence chemical recovery. Despite the general water quality improvements observed to date, some lakes are still highly acidic and elevated levels of copper and nickel persist in the water and sediments of many lakes. Severely damaged biological communities have been slow to recover, probably reflecting a combination of continuing habitat quality limitations and restricted opportunities for dispersal.

Acid rain - perspectives on lake recovery

During the 1970‘s and 1980‘s, the acidification of surface waters by atmospherically deposited sulphur became a major international concern. Large sulphur emission control programs were implemented in Europe and North America with the expectation that many affected aquatic ecosystems would recover. Because of a variety of factors, these positive expectations have been slow to be realized. Only limited evidence of the chemical recovery of acid lakes has emerged from areas other than the Sudbury, Canada region, where sulphur emission reductions were particularly large. Lake response models indicate that when current sulphur emission control strategies in Europe and North America are fully implemented, many lakes will still be acid-damaged even though substantial overall improvements in lake chemistry are expected. An increasing body of evidence indicates that substantial biological recovery, among many groups of organisms,can be expected when chemical conditions improve in lakes. Not all species, however, are capable of unassisted recovery and some lakes can pose biological or physical barriers to colonizers. Thus, stocking may be an important element in management strategies for the restoration of some recovering lakes. Communities in recovered lakes may not achieve pre disturbance conditions, but establishment of typical communities appears to be a reasonable recovery target.

Lake Water Quality Improvements and Recovering Aquatic Communities

In the remote areas to the northeast and southwest of Sudbury, the environmental damage is less visible than in the denuded landscapes near the smelters but is no less severe. These hilly forested areas, underlain by granitic bedrock (Fig. 5.1), contain most of the more than 7000 lakes estimated to have been damaged by smelter emissions (see Fig. 3.2).

Reading the Records Stored in the Lake Sediments: A Method of Examining the History and Extent of Industrial Damage to Lakes

In this chapter, the effects of air pollutants from the roasting beds and smelters on Sudbury area lakes are examined. A rather novel approach has been used to track the lake water quality changes that occurred in the past century. This approach uses the rapidly expanding science of paleolimnology, the study of the fossil record in the lake sediments. In the absence of long-term data, paleolimnological techniques using biological remains in lake sediment cores are being used extensively to provide quantitative assessments of past water quality in North America (Charles et al. 1990; Dixit et al. 1987, 1992c) and Europe (Battarbee et al. 1990).

Liming of Sudbury Lakes: Lessons for Recovery of Aquatic Biota from Acidification

When the pH of lakes falls to less than 6.0, many plant and animal species suffer appreciable damage (see Fig. 5.2). Many species disappear (Schindler et al. 1989). In the 1980s, there were about 19,000 lakes in Ontario with a pH less than 6 (Neary et al. 1990). Roughly one-third of these lakes are near Sudbury. They were acidified by long-term emissions of sulfur dioxide from local smelters (see Chapter 3).

Urban Lakes: Integrators of Environmental Damage and Recovery

Most of the world’s human populations now live in rapidly expanding urban areas (Richardson 1991). These cities and towns vary widely in size and appearance, but they share a common feature: They are near water. Urban waters, in the form of lakes, streams, groundwater aquifers, and the nearshore areas of oceans, satisfy a wide variety of human needs (drinking water, transportation, industrial use, agricultural use, etc.). However, with few exceptions, urban waters have been and are being badly degraded by human activities (NRC 1992). To many, it may therefore be surprising that urban waters, particularly lakes, have received very little study by ecologists in North America (Gilbert 1989; McDonnell and Pickett 1990).

Preservation of Biodiversity: Aurora Trout

The habitat alteration and destruction caused by Sudbury’s metal extraction and smelting industries have contributed to the global depletion of biological resources (Box 11.1). Damage to local terrestrial vegetation and soils, described in Chapter 2, was striking. Less apparent but more widespread was the damage to aquatic ecosystems. Acidification of lakes from atmospheric deposition of smelter emissions occurred over an area of 17,000 km2 and affected lakes as far as 120 km from the city (Neary et al. 1990). An estimated 134 gamefish populations, as well as many populations of less well-studied fish species were extirpated (Matuszek et al. 1992). The loss of these populations did not endanger entire species, but it did contribute to the loss of unique genetic strains The losses are part of an alarming global trend to decreasing fish diversity. By region, the percentages of fish species classified as endangered, threatened, or in need of special protection are as follows: South Africa, 63%; Europe, 42%; Sri Lanka, 28%; North America, 31%; Australia, 26%; Iran, 22%; Latin America, 9% (Moyle and Leidy 1992). Within-species genetic diversity is also declining as fish are extirpated from individual lakes and rivers that comprise portions of their native range (Nehlson et al. 1991; Kaufman 1992).