Acid rain - perspectives on lake recovery

Abstract

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.