CS13 Environmental Ecotoxicology
Date: Friday, June 14, 2002
Time: 10:30:00 AM
Location: Esquimalt
YanND, York University, Toronto, Canada, nyan@yorku.ca
Girard, R, , Ontario Ministry of the Environment, Dorset, Canada, Girardro@ene.gov.on.ca
Keller, B, , Laurentian University Co-op Freshwater Ecology Group, Sudbury, Canada, bkeller@vianet.on.ca
Heneberry, J, , Laurentian University Co-op Freshwater Ecology Group, Sudbury, Canada, jheneberry@nickel.laurentian.ca
Dillon, P, J, Trent University, Peterborough, Canada, dillonpj@ene.gov.on.ca
Gunn, J, , Laurentian University Co-op Freshwater Ecology Group, Sudbury, Canada, jgunn@nickel.laurentian.ca
Long-term recovery in four historically acidic Sudbury lakes: 28 years of incomplete but positive limnological change.
The acidification of lake is accompanied by many changes in water quality, and physical limnology in addition to the impoverishment of biota. It is not yet clear to what extent this damage is reversible. To determine the extent and pace of limnological recovery from extreme damage (eg. lake pH<4.5, all fish eliminated) we summarize 28 years of data from four lakes near Sudbury, Ontario lakes. The pH of two of the lakes (Clearwater and Lohi) has risen from 4.5 to >6 in response to 10-fold reductions in local S emissions. The pH of the remaining two lakes was elevated from <4.5 to >7 by lake and catchment liming in the 1970 and 1980s, and circumneutrality has now been maintained for 25 years. The recovery has been dramatic for many important limnological variables. For example, over the 28 years in Clearwater Lake, pH has increased from 4.3 to 6.4. Nitrate levels have fallen by 4-fold, while organic nitrogen levels have doubled. Dissolved organic carbon concentrations have increased from <0.3 to 2.4 mg/L. The attendant reduction in water clarity has raised the mid-summer thermocline depth from 11m to a more typical 7m, and lowered hypolimnetic heating rates so that mid-summer profundal temperatures have fallen from 15oC to 8oC. Biological recovery is lagging behind recovery in physical and chemical limnology. For example, the zooplankton community has not recovered a typical composition in any of the four lakes, but, encouragingly, several species of fish have successfully colonized the lakes.