ECOSYSTEM RECOVERY AFTER EMISSION REDUCTIONS - SUDBURY, CANADA

A case history is presented describing the ecosystem changes that acco mpanied the nearly 90% reduction of SO2 and metal particulate emission s from Sudbury smelters during the past 25 years. The instances of sev ere ground-level fumigations that caused acute damage to vegetation in an area of approximately 1,000 km(2) have been nearly completely elim inated. Significant improvements in water quality have also occurred i n many of the estimated 7,000 acid-damaged lakes. Several species of a cid-sensitive phytoplankton, zooplankton and insects have invaded lake s where improvements have occurred. Epiphytic lichens have reinvaded t he former ''lichen desert'' that once extended out 7 lan from the smel ters. Sensitive species such as Evernia mesomorpha and Usnea hirta now exist throughout the area. The vascular plant communities have been r elatively slow to recover in the most severely damaged terrestrial are as. Metal-tolerant grasses (e.g. Agrostis scabra, Deschampsia caespito sa) were the first species to invade the barrens. Acid- and metal-cont amination of soil, severe microclimate conditions, and the damaging ef fects of insect pests appear to delay recovery of terrestrial ecosyste ms. Recovery rates of aquatic ecosystems are also affected by a suite of physical, chemical and biotic interactions and many lakes remain se verely damaged.