Soil acidification from acid rain that is harmful to plant and aquatic life has now begun to reverse in forests of the northeastern United States and eastern Canada, according to an American-Canadian collaboration of five institutions led by the U.S. Geological Survey.
The new research shows that these changes are strongly linked to acid rain decreases, although some results differ from expected responses.
"Reduced acid rain levels resulting from American and Canadian air-pollution control measures have begun to reverse soil acidification across this broad region," said Gregory Lawrence, a USGS soil and water chemist and lead author. "Prior to this study, published research on soils indicated that soil acidification was worsening in most areas despite several decades of declining acid rain. However, those studies relied on data that only extended up to 2004, whereas the data in this study extended up to 2014. "
As acid rain acidifies soils, it depletes soil calcium reserves, which are important in preventing the formation of aluminum that is toxic to plants and aquatic life. Calcium is also a nutrient essential for healthy ecosystems. Results of this study show that soils are no longer being depleted of calcium and that toxic aluminum levels have substantially decreased.
The uppermost soil layers have shown a strong recovery response, but deeper layers are actually increasing in aluminum, which suggests further acidification. However, this may be part of the recovery process as aluminum moves downward in the soil to be stored in a non-toxic form.
"The start of widespread soil recovery is a key step to remedy the long legacy of acid rain impacts on terrestrial and aquatic ecosystems," according to Lawrence.
The results were obtained by resampling soils that had been originally sampled eight to 24 years earlier. The collaboration among the USGS, U.S. Department of Agriculture, U.S. Forest Service, University of Maine, Canadian Forest Service and the Quebec Ministry of Forests, Wildlife and Parks, was developed through the Northeast Soil Monitoring Cooperative, a group of scientists focused on how soils are responding to our rapidly changing environment.
The study is available online. Lawrence, G. B., P. W. Hazlett, I. J. Fernandez, R. Ouimet, S. W. Bailey, W. C. Shortle, K. T. Smith, and M. R. Antidormi. 2015. Declining Acidic Deposition Begins Reversal of Forest-Soil Acidification in the Northeastern U.S. and Eastern Canada.Environmental Science & Technology.