Soil health improving in US and Canada, due to acid rain decline

Thanks to pollution regulations, acid rain levels in the northeastern US and eastern Canada are significantly lower today than they were a few decades ago. 

A group of scientists from the United States and Canada have found that the acidity of soils in some parts of the continent has declined, abating years of harm to plants and aquatic life by reversing the depletion of a critical nutrient in soil: calcium.

Scientists have determined this by testing soil samples collected in 27 locations between 2009 and 2014, in the forests of Maine, New Hampshire, Vermont, Ontario and elsewhere in the northeastern US and eastern Canada. They compared their results to those compiled by the same group of scientists working at the same locations between eight and 24 years ago.

"The start of widespread soil recovery is a key step to remedy the long legacy of acid rain impacts on terrestrial and aquatic ecosystems," Gregory Lawrence, a US Geological Survey (USGS) soil and water chemist, said in a statement.

Dr. Lawrence is a lead author of a paper published on October 23 in the journal Environment Science and Technology with researchers from the USGS, Canadian Forest Service, University of Maine, US Forest Service, and Quebec’s parks ministry.

Thanks to pollution regulations in the US (like the Clean Air Act) and in Canada that have curtailed emissions of sulfur dioxide and nitrogen oxide into the atmosphere, acid rain levels today are significantly lower. This is very good news, since acid rain depletes nutritious calcium, a mineral that prevents toxic aluminum from forming in the upper level of soil. This level of soil is dense with nutrients that sustain plant and aquatic life.

Aluminum is naturally found a couple of feet below ground, Lawrence tells The Christian Science Monitor, but it’s not harmful there.

“Acid rain mobilized it and changed it from benign to something harmful,” Lawrence explained. Acid rain forced the aluminum to move from its home deep in the soil to the nutritious upper levels.

This phenomenon caused environmental havoc – poisoning fish, trees, and plants – during peak acid rain levels dating back to the 1970s.

Interestingly, the researchers found that there was actually more aluminum than expected deeper underground, “but that’s probably not because of rain,” Lawrence says. The researchers say that they believe the aluminum is actually moving back to where it came from, says Dr. Lawrence.

“We think this is part of the recovery response,” he says.

The team hopes to next study the calcium levels in the soil, which aren’t declining anymore, but also are not growing. “The most uncertain is the recovery of calcium in the soil,” explains Lawrence. “It seems to be a very slow process and we’re not sure how slow.”