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. "