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Lakes And Streams Taking Time To Recover From Acid Rain

ORONO, Maine – Lakes and streams in Maine and other parts of North America are taking more time than expected to recover from the effects of acid rain, according to reports published this week in the journal Nature and issued by the Water Research Institute (WRI) at the University of Maine. Nevertheless, according to Steve Kahl, director of the WRI, some signs already point to a modest recovery.

Kahl is a co-author of the paper in Nature, "Regional trends in aquatic recovery from acidification in North America and Europe 1980-95." He is a primary author of the WRI draft report to the EPA, "Recent trends and aquatic effects related to acidic deposition in Maine."

Scientists define recovery of a lake as the return to pre-industrial levels of acidity and other chemicals which counteract acidity. So-called "acid neutralizing capacity" is an indicator of a lake’s chemical health. It results from the natural weathering of rocks and soils.

The paper in Nature compares recovery in 205 lakes and streams in five regions of North America and three in Europe. The authors conclude that while recovery is occurring in Europe, four of the five North American regions have not yet shown strong signs of returning to pre-industrial conditions. It is possible, they add, that the supply of acid neutralizing chemicals in rocks and soils has been depleted by decades of acids in precipitation.

Kahl concludes that some Maine surface waters have actually continued to acidify in the past decade despite a decline in sulfuric acid in precipitation. The sulfuric acid trend is an intended goal of the Clean Air Act amendments of 1990 passed under the leadership of then Senate majority leader George Mitchell of Maine. Nevertheless, several factors have so far prevented the expected recovery in lake acidity.

Those factors include variations in climate; continuing elevated levels of nitrogen compounds, such as nitric acid, in precipitation; declines in acid neutralizing capacity in watersheds; increases in naturally occurring dissolved organic acids; the short duration of data collection relative to the watershed processes that influence acidity.

Some signs in Maine point to a modest recovery, says Kahl. They include reduced levels of aluminum in lakes that are sensitive to acid rain and slight increases in acid neutralizing capacity in sensitive lakes.

Elevated acidity has been shown in laboratory and field experiments to have negative biological effects such as reduced fish spawning and toxicity to aquatic organisms from increases in dissolved aluminum.

University Of Maine. October 1999.

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