September 25, 2006

Ecosystems still suffering from acid rain impacts, despite major progress in reducing SO2, NOX emissions

Acid rain-producing emissions of sulfur dioxide and nitrogen oxide (SO2 and NOX) for Canada as a whole are well below the national emission reduction target as well as caps in those jurisdictions that have established them. The 2004-2005 Progress Report on the Canada-Wide Acid Rain Strategy for Post-2000, just released by the Canadian Council of Ministers of Environment (CCME), also notes that Canada is meeting or surpassing its SO2 and NOX emission reduction obligations under various international commitments such as the 1991 Canada-U.S. Air Quality Agreement and UN protocols governing SO2 and NOX emissions.

The latest acid deposition science assessment suggests, however, that this progress, while commendable, may not be enough to enable affected ecosystems to recover from past acid rain damage. The latest scientific research findings indicate that not only is acid deposition still affecting the Canadian environment, the problem is even bigger than originally thought.

Anywhere from 21 to 75% of sampled areas in eastern Canada, including more than half a million lakes, are still receiving levels of acid deposition (in the form of sulfur and nitrogen) exceeding critical loads, says the report. The wide range in exceedance reflects the fact that while the ecosystem can absorb nitrogen as a fertilizer, beyond a certain point it may act like an acid if the ecosystem becomes nitrogen-saturated.

The report notes that lakes and rivers in eastern Canada are still too acidic or have not recovered to the point of being able to support sensitive fish and other aquatic biota. Still, some notable improvements have been made in this region. Lakes near smelters whose emissions have been greatly reduced (e.g. at Sudbury and Rouyn Noranda) have provided the most definitive evidence of recovery.

Because eastern Canada in particular had made significant progress in reducing acid rain-causing emissions, scientists expected that affected ecosystems would recover and aquatic life once abundant in lakes and streams would return. Improved understanding of how damaged ecosystems recover indicates, however, that the most severely affected of them will not return to their "pre-acidification" state once emissions have declined. Some ecosystems, in fact, may require long-term measures such as liming to assist their recovery from acid rain damage, says the report.

Current acid rain research has also begun to focus on its impact on soils, documenting the depletion of nutrients and consequent impacts on the health and productivity of forests, and evaluating the implications of both of these on associated lake ecosystems. The latest information indicates that over 50% of Canada's eastern boreal forests are suffering negative impacts on their growth and productivity linked to acid rain.

This, says the report, could have major socio-economic impacts: preliminary estimates of the market value of lost wood production due to the adverse impacts of acid rain are in the hundreds of millions of dollars in Nova Scotia and New Brunswick alone. Commercial and recreational fishing would suffer as well, and the corrosive effects of acid deposition can be significant, particularly for electrical transmission towers, whose life expectancy could be cut by as much as 50%. As well, notes the report, the effects of acid rain on these structures can greatly increase repair frequency, at an annual cost of thousands of dollars per tower.

The CCME progress report summarizes, in chart form, total SO2 and total NOX emissions by province/territory and by sector. It provides updates on emission reduction initiatives undertaken by the various jurisdictions and outlines next steps to be taken by the CCME's Acid Rain Task Group. Among the main activities being pursued by the group are: supporting the development of a national, multi-year science and monitoring program; further discussing the latest acid rain science assessment to determine what further work needs to be done to ensure successful implementation of the Post-2000 Strategy; and initiating an assessment of possible further policy measures. This could include predicting the magnitude and extent of further emission reductions and the need for management actions to stimulate aquatic recovery and forest sustainability.

Over the next several years, the Task Group intends to determine what short-term and long-term actions are needed by governments, industry, the scientific community and other stakeholders-working individually and/or together-to implement the Post-2000 Strategy, to ensure that Canada is meeting critical loading limits and to promote the recovery of ecosystems from acidification.

The Progress Report may be viewed on the CCME Web site,

Table of Contents  | Top of Page

  Ecolog Network