Assessing the Recovery of Lakes in Southeastern Canada from the Effects of Acidic Deposition

Abstract

Reductions in North American sulfur dioxide (SO2) emissions promoted expectations that aquatic ecosystems in southeastern Canada would soon recover from acidification. Only lakes located near smelters that have dramatically reduced emissions approach this expectation. Lakes in the Atlantic provinces, Quebec and Ontario affected only by long-range sources show a general decline in sulfate (SO4(2-)) concentrations, but with a relatively smaller compensating increase in pH or alkalinity. Several factors may contribute to the constrained (or most likely delayed) acidity response: declining base cation concentrations, drought-induced mobilization of SO4(2-), damaged internal alkalinity generation mechanisms, and perhaps increasing nitrate or organic anion levels. Monitoring to detect biological recovery in southeastern Canada is extremely limited, but where it occurs, there is little evidence of recovery outside of the Sudbury/Killarney area. Both the occurrence of Atlantic salmon in Nova Scotia rivers and the breeding success of Common Loons in Ontario lakes are in fact declining although factors beyond acidification also play a role. Chemical and biological models predict that much greater SO2 emission reductions than those presently required by legislation will be needed to promote widespread chemical and latterly, biological recovery. It may be unrealistic to expect that pre-industrial chemical and biological conditions can ever be reestablished in many lakes of southeastern Canada.

Long-term Trends of Organic Carbon Concentrations in Freshwaters: Strengths and Weaknesses of Existing Evidence

“…However, this would have little sense for many reasons. First, in general: (i) studies cover very different temporal periods; (ii) the number of systems included in each individual study is very different, ranging from one intermittent stream [88] to a major comparison of 705 systems [66]; 33 of the published studies cover less than 10 systems and only 9 more than 100. Curiously, if all trends were pooled together, the existence of four earlier studies [64,66,71,73] covering a huge number of lakes in Canada and Scandinavia (1324 in total), where about 90% of the systems in each study showed no statistically significant trend, would probably give an overwhelming majority for the "non trend" category.…”

Changes in the Chemistry of Small Irish lakes

“…Increases in surface water DOC has been well documented in a number of regions in Europe and North America (Evans et al 2005;Skjelkvåle et al 2001;Kopáček et al 2006;Driscoll et al 2003;Jeffries et al 2003). Although the drivers associated with this increase are speculative, suggestions include decreased acidic deposition, increased temperatures owing to global warming, changes in hydrology and changes in land use (Evans et al 2005).…”

Recovery of Acidified European Surface Waters

“…Since the mid-1980s, sulfur deposition has decreased by ~40% as a result of legislation implemented in Canada (Eastern Canada Acid Rain Programme; 36) and the United States (Clean Air Act Amendments; 37) and the 1991 Canada-U.S. Air Quality Agreement (38). Surface-water chemistry has begun to recover (11,(39)(40)(41)(42). Additional reductions in sulfur deposition may occur in the future.…”