Forests can bounce back after acid rain

acid rain forests bounce back, sweet woman in the forest

Even though 70s and 80s suffered through Acid Rain, new research shows that forest soils can bounce back. You see, there is still hope that we can solve climate change.

If you grew up in the 70s or 80s no one was talking about climate change: they were talking about nuclear war and acid rain. Acid rain made Kimberly’s hair turn green in the TV show Different Strokes; Canada’s environmental minister called it the “malaria of the biosphere” and it kept me away at night worrying.  Acid rain was the fallout of industrial chemicals and pollution into forests and lakes. As it rained toxins were picked up by the water and the toxins were rained down in close and faraway parts of the world. 

Canada suffered a massive amount of acid rain from the United States as it blew northward. The Ukraine and the rest of Europe experienced more than acid, but nuclear rain, after the Chernobyl meltdown.

So in the 60s and even into the 70s, before the American Clean Air Act of 1970 came into full effect, rainfall over the United States and Canada was full of acid. It killed lakes all over Canada and I remember canoeing in beautiful, but dead, lakes when I was a kid. We talked about it all the time. Acid rain was a thing. 

Acid rain is precipitation that mixes with gases from industrial plants, emissions from cars, and especially coal and fossil fuel pollution. That caused the water to become acidic – also called “acid rain.” Coal plants can also actually cause rain. Read this article about it

Besides the air pollution hurting plants and humans and lakes, this acid rain also hurt our soil. Even dry deposits of these acidic emissions could be hurtful to humans, plants, soil and water. Acidic soil can bind nutrients so that plants can’t get them. It can hurt the microbes in soil, as well as plants. But new research suggests that soils can bounce back. 

One odd “helpful” thing acid rain did, though, researchers had found, was to provide a few nutrients to the soil. The sulfur in the acid rain – in the form of sulfates – actually provided nutrition to plants.

However, the benefit was negligible, and the overall effects of pollution required regulation. Occasionally, cities like Los Angeles will still experience “smog.” The incidents are even more common in China and India, where little regulation is in effect. (Read this good BBC article on the bittersweet story of solving acid rain).

Jennifer Knoepp, with the US Forest Service, has been studying how the reduction of air pollution and acid rain is affecting forests in the southern Appalachian Mountains. Her interest is to see how soils are recovering as our air gets cleaner.

acid rain soils recovering, sampling of forest soil

How does soil fare after the Clean Air Act?

Both the 1970 Clean Air Act and 1990 Amendment regulated emissions across the United States, resulted in improved air and water quality. But what about the soil – the “skin” of the earth – that provides for food and shelter and is home to the world’s largest biodiversity?

“We have found significant movement of sulfate from the soils over time,” says Knoepp. “Sulfate is moving out of the surface soils and into the subsoil. In addition, the streams in our study site show improved water quality. However, soils and streams still exhibit chemical imbalances. This suggests recovery from decades of acid rain is a long-term process.”

forest bathing, woman hipster contemplating nature in dark green forest

To evaluate the soils and water, researchers sampled 24 high elevation spruce-fir forest sites and two watersheds in the southern Appalachians. The sites represent a region in the southeastern U.S. with high gradients in elevation and precipitation, as well as high biodiversity.

The research area includes sites within the Great Smoky Mountain National Park and the southern end of the Blue Ridge Parkway. Both are major tourist and outdoor recreation destinations. 

Recent soil collections were compared to archived soil samples from the 80s and 90s. Sample archives are essential to long-term research. They provide the ability to conduct tests not planned during an original experimental design. 

testing forest soil for acid rain

The research team analyzed both the newly collected and archived samples for “extractable sulfate.” All data were used to determine the long-term response of southern Appalachian forests to changes in sulfate deposition that occurred after the implementation of the Clean Air Act Amendment in 1990.

Data show that sulfate in precipitation and streams declined after implementation of the Clean Air Act Amendment. They also show that completely reversible sulfate has declined in surface soils. Sub-surface soils show either no change or an increase in partially reversible sulfate.

Knoepp presented her work at the November International Annual Meeting of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America in San Antonio as the Sergei A. Wilde Distinguished Lectureship on Forest Soils. 

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