Acid Clouds

Wind-blown clouds more than rain are bringing the acidity that is destroying high mountain forests of the northeast, according to Dartmouth researchers led by biology professor Williams Reiners. This has been confirmed by studies made 4,000 feet up on Dartmouth's Mt. Moosilauke.

According to Reiners, "The forests at upper elevations in the northeast look terrible. Spruce in particular are dying, and we know this is a recent phenomenon. I don't know for sure what has led to this massive recent decline of the high forests, but our findings certainly lend support to the idea of increased correlation between that decline and the concentration of acids and trace metals occurring in the soil there." The Dartmouth research has been reported in the magazine Science in an article co-authored by Reiners.

In recent years, many researchers have reported the dying of forests on New England mountains of 4,000 feet or more. The likely cause, it has been suggested, is acid rain, containing harmful substances released into the atmosphere from the industrial midwest. Just as destructive, if not more so, Reiners believes, are the windblown clouds which deposit up to a third of the moisture the high mountains are receiving. And cloud droplets, he says, are far more concentrated than raindrops. Reiners has found that while Mt. Moosilauke's high forests are getting one-third of their precipitation from clouds, more than 60 percent of their acidity is coming from this source. Among the harmful substances brought by wind-blown fog droplets are excess hydrogen ions, the basis of acidity, and trace metals.

The balsam fir forests around 4,000 feet are ideal mechanisms, Reiners found, for trapping moisture from wind-blown clouds. Needles, he has determined, are more effective moisture traps than broad leaves. The lichen-covered trunks of the fir also capture moisture well. The highest capture of moisture occurs at around 4,000 feet. At that height, clouds are usually present and wind speed and tree height are ideal.