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

Aquatic ecosystems in a 17,000 km super(2) 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 the 1990'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.