Acid Rain Linked to Damaged Lakes
Peterson, Ivars, Science News
Acid rain linked to damaged lakes
Locked in sediments beneath many freshwater lakes is a fossil record of water acidity stretching back hundreds of years. These records are among the many pieces of evidence that have now led a National Academy of Sciences (NAS) panel to conclude that acid rain has damaged lakes in the northeastern United States.
Although some scientists had long suspected that such a connected exists, others had proposed alternative explations for fishless acid lakes -- from natural acidification to the effects of farming and lumbering (SN: 3/17/84, p. 164). The NAS study released last week, "Acid Deposition: Long-Term Trends," suggests that in certain cases, none of the alternative explanations accounts for lake acidity as fully as the effect of sulfur dioxide emissions from the burning of fossil fuels and the resulting acid deposition.
"The connection between acid rain and environmental damage is real," says James H. Gibson of Colorado State University in Ft. Collins, who chaired the panel, "but it is more variable and complex than many people have supposed." Individual lakes vary widely in their response to acid rain, he says. Nevertheless, the report goes a long way toward linking sulfur dioxide emissions with lake acidification. According to the Academy, this report is "the most comprehensive effort to date" to document acid rain causes and effects.
One important element in the study was the analysis of sediment cores taken from lake bottoms. The number and types of fossil microorganisms called diatoms found in different layers of these sediments provide a sensitive measure of lake acidity. "Diatom analysis is the best technique that we have available for inferring past [acidity] histories of lakes," says biologist Donald F. Charles of Indiana University in Bloomington.
The researchers discovered that natural acidification normally occurs over hundreds or thousands of years. …