A forest watered by acid rain may be less able to slake its thirst.
That’s one finding from a decades-long experiment in the Appalachian Mountains, where the U.S. Forest Service since 1989 has been dousing a 34-hectare patch of forest with an acidifying ammonium sulfate fertilizer three times a year. The chemical served as a proxy for acid rain, which is created when sulfur and nitrogen containing compounds released by industrial activities, agriculture and the burning of fossil fuels acidify raindrops.
In most of the years from 1989 to 2012, the acidified forest soaked up around 5 percent more water than a neighboring, 39-hectare untreated area — and up to 10 percent more in two of the years, researchers report July 31 in Science Advances. Levels of calcium, a nutrient plants need to retain water, in the water that permeates the soil of the acidified forest also declined over the study period, which could explain the forest’s water guzzling.
“We didn’t expect that plants actually will respond so strongly to acidification,” says ecohydrologist Lixin Wang of Indiana University-Purdue University Indianapolis. That may be cause for concern, he says: Thirstier plants could contribute to droughts or leave less water available for people and other animals.