Human-caused climate change is THE environmental issue of our times.

Alarming reports point out that we’re already seeing the effects of a warming planet and predict dire consequences if we don’t get a handle on our fossil fuel addiction — and soon.

But before climate change, there was acid rain. Back in the 1980s and 1990s it was the THE environmental issue of the time.

Bear Brook Watershed StudyThe good news is, we took action to curb acid rain and saw substantial improvements. The problem hasn’t gone away, by any means. In some parts of the world, like Russia and China, it is severe. It’s still bad in some areas of the U.S. But acidification of soils and lakes in the northeastern U.S. has dropped. And in that way it perhaps can serve as a lesson about how we can solve our latest major environmental problem of climate change. After all, they both derive from the same source — burning fossil fuels.

Here’s a primer on acid rain:  vehicles and coal and oil-burning power plants emit air pollution — particulates, carbon dioxide, but also sulfur dioxide and nitrogen oxides. Once in the atmosphere, the last two pollutants react with water molecules to form sulfuric acid and nitric acid, which, when they fall from the sky as rain or snow can acidify lakes and ponds, killing fish and other aquatic organisms, damaging forests, accelerating the weathering of steel bridges and harming human health.

Acid rain has been around since the beginning of the industrial revolution. As early as the 1600s peopleAcid Collector on Bear Brook with Catwalk noticed how polluted city air was corroding marble buildings and statues. In 1852 a Scottish chemist named Robert Angus Smith linked air pollution to acid rain and in so doing earned the not-so-glorious nickname of “Father of Acid Rain.”

In the U.S. acid rain vaulted into the news after scientific studies showed serious effects from acid rain in the White Mountains of New Hampshire. Specifically the Hubbard Brook Valley. The thing about acid rain is that it’s a long distance pollutant. The acid rain that fell on the White Mountains and Maine and the Adirondack Park in New York State mostly originated in the car-clogged big cities to the south and the stacks of the big coal-fired power plants of the Midwest. The pollution rode the prevailing winds to more remote parts of the Northeast. The effects were felt far downwind.

In 1980 Congress authorized a long-term research program on acid rain. Ten years later it passed amendments to the Clean Air Act, championed by Maine Sen. George J. Mitchell, that directly tackled the acid rain issue primarily by limiting sulfur emissions from power plants by almost 50 percent and creating a cap-and-trade system designed to control sulfur dioxide and nitrogen oxide emissions.

It worked.

“Acid rain is still out there, but we have made huge gains,” said Ivan Fernandez, a professor at the University of Maine’s Climate Change Institute and the School of Forest Resources who has done extensive research on air pollution and forest ecosystems. One of his projects is a nearly 30-year study of two watersheds in eastern Maine that looks at what happens when you add extra nitrogen to forest soils.

Hubbard Brook WatershedFernandez said there is “about 75 percent less sulfur deposition and about 50 percent less nitrogen deposition here in Maine, with important improvements evident particularly in surface waters.”

Maine still has “way more acid rain than Oregon, for example, but we are far better off than we were,” Fernandez added.

Acid rain is still a serious problem farther south, though. In the Great Smoky Mountains National Park on the Tennessee-North Carolina border, the average acidity of rainfall is 4.5. That’s 5 to 10 times more acidic than normal rainfall, which has a pH of 5.0-5.6, according to the Great Smoky Mountains National Park’s website, last updated in 2015. “Clouds with acidity as low as 2.0 pH bathe the high elevation forests during part of the growing season” the Park’s website adds.

The Smokies, among the highest mountains in the east, tend to trap pollution flowing from the west, according to the Park’s website. In addition to acid fog and rain, average visibility in the mountains is only 25 miles, compared to nearly four times that under natural conditions. And ground-level ozone, a throat irritant, is two times higher on the ridgetops than in nearby cities.

In the Smokies, according to the Park, high elevation soils get so much airborne nitrogen they are become saturated with the element, something that limits the availability of forest nutrients, especially calcium, to plants and causes the release of toxic aluminum that can hurt vegetation and streamlife.

Nitrogen is something of a double-edged sword. It’s an essential nutrient for plants, but you can have too much of a good thing. Fernandez’ Bear Brook project, which began in 1989, looked at what happens when nitrogen increases. Two nearly identical drainages were used. One was regularly seeded with ammonium sulfate fertilizer to simulate increased nitrogen and sulfur from acid rain, the other was used as a control. One thing the researchers discovered: more nitrogen accelerates loss of calcium and magnesium in the soils.

“It’s in the remote regions like a lot of Maine where there’s not intensive human activity that the atmospheric deposition plays a dominant role in acidification of surface waters,” Fernandez said. In fact, many northeastern forest soils tend to be naturally acid. “The forest floor in a conifer stand might be in the range of 3.0 pH,” he said. But the sulfates and nitrates in acid rain strip calcium — another essential nutrient for plants — from the soil and dissolve aluminum that’s naturally present in the granite rocks of the northeast. When that aluminum washed into lakes it proves toxic to fish and other aquatic organisms, killing them.

But sulfate levels dropped and aluminum mobilization decreased and lakes recovered after Congress took action, Fernandez said.

Environmental Trees damaged by Acid RainInterestingly, as the pH of forest soils has gone up, it seems to have led to an increase in dissolved organic carbon, also known as DOC, that colors lakes and streams brown. That doesn’t seem to have any effects on forest health, though when it leaches into a lake, a little more dissolved organic carbon might lead to less light penetration that alters lake temperatures and biology, he said.

While there have clearly been benefits to surface waters from acid rain reduction, the effects on forest growth in Maine are a little less clear, he said. “It’s a complex and variable ecosystem,” he said. There are too many variables to get a handle on without a huge — and expensive — research program.

Over the last couple of decades research on acid rain has dried up. Pun intended. These days everything is climate change and greenhouse gas pollution.

Unfortunately, very little research in Maine is looking at how still-existing acid rain and climate change work together to affect forest ecosystems, Fernandez said.

Forests in the 21st century in Maine so far likely benefit from longer growing seasons, more rain, less acidity from sulfur deposition and rising carbon dioxide concentrations, Fernandez said. “However, we also are getting less nitrogen from air pollution, and nitrogen is the most limiting nutrient in forests, and we are uncertain how this mix of changes affects insects and disease as well as forest composition in the future.”Ecology damaged by Acid Rain

Forecasts for increased precipitation in the northeast might, say, mean more water washing through soils and leaching out pollutants, which could speed up recovery, but could also wash away essential nutrients faster, slowing recovery. But no one knows.

We learned a few things from our experience with acid rain, not all of them associated with the chemistry of the problem.

For instance, we learned that legislation informed by science can craft a solution that works. And, we’ve learned that predictions of economic catastrophe associated with those solutions sometimes don’t occur:  the Environmental Protection Agency posited in 2007 that the costs of dealing with acid rain by 2010 would be $1 to $2 billion a year, about a fourth of what had been predicted.

And efforts to rein in sulfur and nitrogen pollution had other benefits beyond revitalizing trout streams in remote areas of the northeast. They also helped reduce particulates and ozone and curbing those pollutants led to substantial human health benefits.

And that raises the question of what would happen if we worked aggressively to reduce CO2 emissions toAcid Rain Damage head off climate change. That would undoubtedly help further reduce sulfates and nitrates in air pollution, further reducing acid rain. An effort on one front would bear benefits on others.

These are referred to as co-benefits, Fernandez explains, and they can add a lot to the benefits for society. In 2011, the Environmental Protection Agency issued a report stating that the benefits of the Clean Air Act between 1990 and 2020 paid back over $30 for every $1 invested in reducing pollutants.

Right now the big question is not whether some new initiative to further combat acid rain will be undertaken. It won’t. The question is whether the successes in a decades-long battle will be undermined, or reversed, by a White House administration that has touted the benefits of burning coal and has worked aggressively to roll back environmental regulations on a variety of fronts.

A major new report by 13 federal agencies was released on the day after Thanksgiving. It said the U.S. is already feeling the effects of climate change and warned that by the end of the century the annual costs in the U.S. could approach $500 billion: in lost labor, damaged crops and extreme weather events.

The White House downplayed the report’s conclusions and President Donald Trump said he didn’t believe it.

The U.S. used science to “put good policies in place to reduce acid rain and 30 years later . . . the improvements are detectable,” said Fernandez. A move to do away with the regulations that made those improvements possible would be shortsighted, he said, especially given that there’s no scientific basis for it.



Joe Rankin writes about forests, nature and sustainability for websites and magazines. He lives in New Sharon. 

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