Acid rain forms when various polluting gases are incorporated into rainwater. This can affect buildings and crops. It can also make trees thirstier. In a long-running experiment by the U.S. Forest Service, it was found that the effect of an acid rain equivalent was to decrease the capacity of trees to retain water.
Studying the Effects of Acid Rain
The study has been running in the Appalachian Mountains since 1989. A forest area extending for 34 hectares has had an ammonium sulfate fertilizer applied to it three times every year since then. This fertilizer is acidifying and therefore approximates acid rain. Normally, acid rain forms when industrial air and other forms of exhausts release sulfur and nitrogen gaseous compounds into the atmosphere.
The U.S. Forest Service set out to study the effect of acid rain on forestry. It found that the acid treatment resulted in around five percent more water uptake between 1989 and 2012. This was in comparison to a nearby, similar forest area that was not treated with the acidic fertilizer. The water uptake increased by as much as 10 percent in a couple of the years looked at. The results of this decades-long study have been published in Science Advances.
Another measure of interest from the study is the calcium level in the soil. Plants require this mineral to help them retain water. The treated forest patch had less and less of it in the soil as the study progressed. The acid affects the level of calcium that is retained in the soil.
The study is significant for a number of reasons. It is the first time that the effects of acid rain have been studied on such a large scale of forest area. Previous investigations worked on much smaller plots. Another important takeaway is the role of soil minerals in water retention and how difficult these are to recover once they are leached out.