Science / Medicine : ACID LAKE : Research on Wisconsin Lake May Provide Glimpse of Long-Range Effects of Acid Rain
Except for a few scientific instruments strewn along the shore and a black vinyl curtain stretched across a narrows, Little Rock Lake resembles many others in a section of northern Wisconsin that has one of the world’s thickest concentrations of lakes.
But the lake’s snowy blanket, and its surrounding evergreen forests, disguise a sour truth: Pollution from fossil fuels is responsible for a tenfold increase in the acidity of rainfall in this area.
While all 1,300 lakes in Vilas County get a steady dose of acid rain, only Little Rock receives extra splashes of acid--from the scientists who have transformed it into a vast test tube for acid rain research.
In an effort to understand the biological and chemical effects of acidification on a lake, these researchers are deliberately hastening the pace and watching the results.
Vulnerable to Acid
Lakes vary in their ability to neutralize acid--the wet and dry forms of sulfuric and nitric acid commonly called acid rain. Little Rock Lake is similar to about 1,200 lakes in Wisconsin that are extremely vulnerable to acid rain and the attendant loss of fish and other species it can cause. Not only does the lake’s water carry little alkalinity, but it receives little runoff and ground water. Essentially, one scientist said, Little Rock is a “basin for rainfall.”
After selecting Little Lake and obtaining permission from the state Legislature, about 30 scientists began the study in 1984. At that time, the lake was slightly acidic, with a pH level of 6.1. (Acidity and alkalinity are measured in pH units: 7.0 is neutral; numbers above that are alkaline, and those below are acidic. Each whole number difference marks a tenfold change in acidity, so pH 4.6 is 10 times as acidic as pH 5.6.)
The scientists divided the 45-acre lake with the vinyl curtain and monitored it for a year before beginning acid treatments. In 1985, they started pouring sulfuric acid into the side they call the “treatment” basin, reducing the pH to 5.6.
Last year, they increased the acidity to pH 5.1, all the while comparing the chemistry and biology of the treatment basin to that of the untreated or “reference” basin. And next year, when the treatment basin reaches pH 4.6--as acidic as the rain it receives--the scientists will send their data to Washington, where it will probably become ammunition in a continuing congressional wrangle over regulating acid pollution.
Findings Emerging
With the project about half completed, findings are beginning to emerge. Only half as much acid as expected has been used to reach acidity targets, indicating that the lake is more susceptible to acid than predicted.
One species of plankton--the free-floating organisms that underlie the food chain--is declining and another increasing, both due to changes in reproduction. University of Wisconsin-Madison limnologist Thomas Frost reports “some indications” that bass reproduction is abnormally slow.
A more prominent change is a “bloom” of long, stringy algae that has begun carpeting the treatment basin. Carl Watras, director of field work, explains how an increase in this one species could affect many aspects of the lake. For example, the algae offers good cover for minnows, so “a meal could cost more energy to a predator,” Watras said.
In addition, the algae could be “an enormous food source” for animals living on the bottom, so they can be expected to increase. Finally, it appears to be crowding out plants whose roots help stabilize the lake bottom. The scientists say these are the kinds of changes that can only be investigated by manipulating an ecosystem.
The experiment bridges a gap between observation of lakes--which is slow and cannot prove cause-and-effect relationships between acid rain and lake damage--and laboratory experiments, where the complexities of real lakes don’t always intrude.
By manipulating the lake and confirming results with lab tests, the scientists hope to reduce the uncertainty that has forestalled actions to control sulfur and nitrogen oxide pollution.
Information from the project could influence whether eastern North America continues receiving about 15 pounds per acre of sulfuric acid each year, or whether the United States follows the lead of Canada and states such as Wisconsin that already regulate sulfur oxide emissions.
While rain has been unnaturally acidic since the widespread burning of coal during the 1800s, the problem began affecting wider areas during the 1960s and ‘70s, when tall smokestacks were built to abate pollution near power plants.
Acid emitted from today’s stacks, which are as tall as 1,000 feet, can drift hundreds of miles before returning to the surface. Thus, Wisconsin’s controls on acid emissions will have only a limited effect on the rain around Little Rock Lake, which also contains acid from other states and Canada.
Sulfur oxides, which are emitted by electric generators and industrial boilers, are transformed into sulfuric acid in the atmosphere. They are the primary reason that rain in the 31 states bordering on or east of the Mississippi River is as acid as pH 4.0, about 25 times as acid as “natural” rain. (Unpolluted rain, pH 5.4, is weakly acidic because carbon dioxide combines with water to form carbonic acid.)
In the West, the acid rain problem is mainly due to nitric acid from vehicle exhaust.
The experiment is part of a federally funded National Acid Precipitation Assessment Program. The program, a cooperative effort of various U.S. government agencies, also sponsors research into production and airborne circulation of acid pollutants, as well as how acid rain affects human health, forests, crops and buildings.
The Little Rock project, being directed by the U.S. Environmental Protection Agency, is the only such experiment under way in the United States. But plans are being made to acidify a stream watershed and a lake, both in Maine.
Delegated Responsibilities
The research plan gives University of Wisconsin-Madison responsibility for studying plankton; University of Wisconsin-Superior for fish; the U.S. Geological Survey for ground water; the University of Minnesota for water chemistry, and the Wisconsin Department of Natural Resources for the lake bottom.
The National Acid Precipitation Assessment Program grew out of a dispute among Eastern legislators, environmentalists and the Canadian government, all favoring emission controls, and the Reagan Administration and legislators from the Midwest states that produce and burn high-sulfur coal, which have pushed instead for research.
In working for a research project that the Reagan Administration offered instead of acid rain regulations, the Little Rock scientists are in a peculiar position. While they know better than most that acid rain destroys some lakes, they are hard-pressed to complain because the political stalemate has made research money available to a field that normally doesn’t get much.
Limnologist Frost, a project leader, acknowledges that some people saw the assessment program as a “smoke screen” for the Administration’s refusal to control emissions.
“We clearly know enough about acid emissions to realize they’re harmful,” he responds, “but we don’t know enough to stop research.”
While damage to lakes in New York, Ontario and Scandinavia is irrefutable, the mechanism is unclear to scientists: Is acid directly toxic to fish, or does it interfere with the food chain? What pH is damaging each of the major categories of lakes?
The Little Rock group hopes to nail down answers to some of these questions. “You can always postulate several different mechanisms for changes in lakes hit by acid rain,” Frost explains. “Not until you do the experiment to eliminate alternative explanations can you conclude what’s happening.”
Fish Disappearance
Modern concern about acid rain dates to the 1960s when scientists traced the disappearance of fish from some Scandinavian lakes to rainfall.
In 1976 limnologist David Schindler began the first ecosystem-scale experiment on acid rain by gradually increasing the acidity of a lake in Western Ontario. As the pH fell, he found problems with fish reproduction sooner than expected.
Schindler, at the Freshwater Institute in Winnipeg, Manitoba, has since manipulated other lakes and found, for example, that nitric acid is less damaging than sulfuric acid.
Aside from its susceptibility to acid rain, Little Rock Lake had the additional advantage of being near the University of Wisconsin’s Trout Lake Research Station. The foundations of limnology--the study of fresh waters--were laid here in the 1920s by University of Wisconsin scientists Edward Birge, who discovered the basic thermal mechanism of lakes, and Chancey Juday.
While Birge and Juday described lakes, other University of Wisconsin scientists manipulated them. During the early 1950s, Arthur Hasler, a student of Juday, tried to boost fish production by neutralizing a naturally acidic lake. He did raise its pH, but never created the trout haven he sought.
The ability of lake manipulation research to settle environmental disputes was proven during the 1970s when it was found that phosphorous from detergents was fertilizing algae that clogged lakes. Limnologist John Shearer worked with Schindler on an experiment that demonstrated the relationship.
“There had been quite a bit of opposition from detergent manufacturers,” Shearer said of proposals to ban phosphorous. “After that, the opposition pretty well died out.”
THE pH SCALE Measuring Acidity Acidity and alkalinity are measured in pH units 7.0 is neutral; numbers above that are alkaline, and those below are acidic. Each whole number difference marks a tenfold change in acidity, so pH 4.6 is 10 times as acidic as pH 5.6
pH level Ratio Scale Battery Acid 1 1 million Lemon Juice 2 100,000 Vinegar 3 10,000 Acid Rain 6 10 Pure Water 7 0
How Pollutants Become Acid Rain
Eastern North America now receives 15 pounds of sulfuric acid each year--falling to the earth through polluted rain and snow.
While rain has been unnaturally acidic since the widespread burning of coal during the 1800s, the problem began affecting wider areas during the 1960s and ‘70s, when tall smokestacks were built to abate pollution near power plants.
The effects of acid rain on human health, fish, forests, crops and buildings are becoming a more significant national concern.
Acid emitted from the towering smokestacks can drift hundreds of miles before returning to the surface.
Sulfur oxides are created by the burning of coal, oil and gas by heavy industry and electrical utilities. They escape through smokestacks to the atmosphere, along with oxides of nitrogen from automobiles.
Through complex processes, the sulfur and nitrogen oxides are converted into acids by sunlight and catalysts.
The acids become waterborne in raindrops or snowflakes and fall to earth.
