How Acid Rain Research at Little Rock Lake Improved Our Air Quality
Years ago Dave Daniels from Rhinelander heard of a research project that really interested him, but he never heard what came out of the project so he sent a question to WXPR’s Curious North series asking us to look into it: What ever became of the Little Rock Lake Acid Rain research project conducted by water scientists at the Trout Lake research station near Boulder Junction?
For this month’s Field Notes, Susan Knight recounts the entire story of Little Rock Lake, the site of an experiment studying acid rain, and the results that led to better air quality for everyone.
This is a story about a small lake in Vilas County, an audacious experiment, and the results that led to national improvements in air quality. Little Rock Lake is a seepage lake nestled in the Northern Highland American Legion State Forest that, for more than a decade, was the site of an elaborate experiment testing the effects of acid rain on soft-water seepage lakes. Seepage lakes such as Little Rock Lake do not have any streams coming in or going out -- making most of them very low in minerals -- and are common in northern Wisconsin.
Acid rain became a concern back in the 1970s and 80s, especially in eastern US, in places such as the Adirondack Mountains in New York. Acid rain is created when coal-fired power plants release sulfur and nitrogen compounds into the air. Those compounds react with other chemicals in the atmosphere and are converted into sulfuric and nitric acids. These acids mix with moisture in the clouds and then fall as acid rain or snow. Unfortunately, the Adirondacks were right in the crosshairs of prevailing winds coming from power plants in the Ohio River Valley and were hit hard by acid rain.
Soils and lakes have some capacity to neutralize acids, and this is known as their buffering capacity. Our stomachs also have some capacity to neutralize acids. If your stomach is overwhelmed with acid, you can take something like Alka-Selzer to neutralize it. Unfortunately, there is no Alka-Selzer you can add to a lake. Once the acid rain exhausts a lake’s buffering capacity, the lake becomes highly acidic. Because of their geology and chemistry, the Adirondack soils and lakes have a very limited buffering capacity, and the acid rain overwhelmed their ability to neutralize the acid precipitation.
The Adirondack lakes were especially hard-hit by acid rain. The greater the acidity, the fewer fish species the lakes had and in highly acidic lakes, there were no fish at all. People were worried the same thing could happen here in the Midwest.
To test the vulnerability of our Midwest lakes to acid rain, scientists decided to experimentally add acid to a lake and watch what happened to the lake’s plants, animals, and chemistry. When doing an experiment, it is critical to have a control, but doing so was tricky in this situation. The researchers decided they would conduct the experiment all in one lake, but that they would divide the lake in half. One side of the lake would be acidified, and the other side would act as a control. Little Rock Lake was chosen partly because it is vulnerable to acid rain but also because it is hour-glass-shaped and could be easily divided with a curtain at the narrows.
You may remember from high school chemistry that a low pH means that something is more acidic. In the Little Rock Lake experiment, researchers added acid to lower the pH in three steps; the pH was first lowered by a half pH unit for two years, then another half pH unit for two years and finally another half pH unit for two years. In the end, the pH of the lake matched the pH of the rain in our area, or 4.6. How did scientists acidify the lake? Technicians drizzled acid from a hose trailing out the stern of a boat, and then sped around to mix the acid evenly through the lake.
As in the Adirondack lakes, fish living on the acidified side of Little Rock Lake were hit hard. The youngest fish were most vulnerable, and some fish species were unable to successfully reproduce. Zooplankton, the microscopic shrimp-like creatures fed on by fish fry and minnows, were also affected. The acidic side of the lake was also clearer, which created billowing clots of algae near the bottom.
The study also found that mercury levels were much higher in fish when the pH was at its lowest levels. The increased acidity encouraged the growth of acid-loving bacteria. As a byproduct of their metabolism, these bacteria converted mercury into a chemical form that could enter the food web. The mercury became more concentrated as it moved up the food web and into the fish we like to eat. Mercury is toxic and high mercury levels are responsible for warnings about eating fish from many of our lakes.
So, was it worth it? The study at Little Rock Late resulted in more than 100 papers, encouraged an international dialog, and ultimately led to congressional action and a decrease in acid rain. The results showed that Wisconsin lakes are susceptible to acid rain and established clear connections between lake chemistry, acid rain, fish reproduction, and mercury contamination. Several of the scientists testified in front of Congress, supporting both the Clean Water Act of 1987 and the Clean Air Act in 1990. Since these congressional actions, the acidity of the rain has decreased, and the threat of acid rain has lessened -- quite a legacy for a quiet little Northwoods lake!
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