Acid Precipitation

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In the Adirondack Mountain region of New York (which has been the hardest-hit area of the U.S.), over 200 lakes are now considered acidified, with an average pH of less than 4.5. (Remember, that's 500 times more acid than a normal lake.) To the north—in Ontario, Canada-400—lakes have been lost to acid precipitation, and 48,000 more are threatened. (And despite the prodigious emissions of the nickel plant in Sudbury, it's estimated that two-thirds of Canada's acid precipitation results from airborne contaminants produced in the U.S.A.)

In order to appreciate the potential damage we're talking about, it's important to understand what happens when a body of water goes acid. More than 50% of the lakes with pH readings of less than 5 have no fish at all. Even at pH6.5 the reproductive capacity of most trout species begins to drop ... and the fry that do survive are increasingly prone to genetic defects. Often, the first hint that a lake is going acid comes from people who fish there, when they report a limited catch of large fish (which grow rapidly as a result of not having to compete with new generations for food) and few, if any, smaller ones.

However, scientists believe that the eventual death of the fish population in an acid lake isn't caused directly by the low pH. Rather, it's thought that toxic metals which are mobilized by the acid precipitation—aluminum and mercury are the two most prominent offenders—do most of the damage.

Other forms of aquatic life are also severely affected by low pH. The bacteria that are normally present in freshwater lakes tend to die back as pH drops, while fungi are more likely to thrive. Consequently, organic matter (such as falling leaves) accumulates on the lake's bottom instead of being consumed. In fact, so many bacterial organisms, which are normally suspended in the water, die off that acid lakes are often very clear. (A sure sign of a lake with low pH is the growth of sphagnum moss on the bottom . . . since that plant can adapt to an aquatic life only in acid water.)

Because it's been less than ten years since scientists began to study the effects of acid rain, our understanding of the problems it causes is by no means complete. While we are beginning to catalog the effects of low pH on freshwater lakes, research into the actions of acid precipitation upon complex land-based ecosystems has barely started.

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