Arnott, S. E. York University c/o Dorset Environmental Science Centre,
Yan, N. E. Ontario Ministry of Environment, Dorset Environmental Science Centre,
Keller, W. Cooperative Freshwater Ecology Unit, Biology Department,
Nicholls, K. Ontario Ministry of Environment, Laboratory Services Branch, Aquatic Sciences Section,
Gunn, J. M.. Cooperative Freshwater Ecology Unit, Biology Department,

The recovery of lakes from acidification may be interrupted by the interaction of multiple stresses, including climate change, re-acidification, and increased UV-B irradiation. We followed the recovery and re-acidification of Swan Lake, Sudbury, Canada from 1977 to 1997. In 1988, pH declined from 5.8 to 4.5 resulting from the oxidation of sulphur compounds in the watershed and littoral sediments exposed to the atmosphere during two previous years of drought. Associated with the drop in pH was a 3-fold decline in DOC concentration, a 3-fold increase in UV-B penetration, and a 10 degree C increase in summer bottom-water temperatures. Considerable biotic changes occurred. Phytoplankton richness and biomass declined. Rotifer and crustacean diversity declined, but crustacean richness increased, primarily because of rare species. The cladoceran community became dominated by littoral species such as Chydorus sphaericus and there was a 10,000-fold increase in Leptodiaptomus minutus, an acid-tolerant species. These changes likely resulted from acidification, increased UV-B penetration, changes in lake thermal structure, and changes in community interactions. Because of strong linkages among climate variability, drought, acidification, and increased UV-B penetration we must consider the influence of multiple stressors as we seek to understand regulators of recovery in aquatic ecosystems.
Day: Wednesday, Feb. 3
Time: 11:00 - 11:15am
Location: Sweeney Center
Code: SS50WE1100S