Air and Acid Rain--Status and Recommendations 
Paul W. Hansen (1) 
Over the past several years, reports of rapid and 
devastating forest declines in Europe and reports of 
forest decline, dieback, and reduced growth rates in 
North America have focused an increasing amount 
of attention and concern on the role of air pollutants, 
particularly sulfur compounds and ozone, in the for- 
est ecosystem. In each case, forest damage is oc- 
curring in regions receiving high loads of acidic and 
other pollutants, and these air pollutants are impli- 
cated to some extent in virtually all of the forest 
declines. 
One of the problems that has plagued the acid 
rain issue, since its recognition as a serious environ- 
mental threat, is the establishment of irrefutable 
cause-and-effect relationships between pollutants 
and environmental impacts. The complexity of eco- 
logical and chemical relationships means that we 
Cannot enjoy the certainty we would all prefer to 
have as we make important policy decisions on pol- 
lution control. This has been particularly true re- 
garding air pollutants, acid precipitation, and the 
forest ecosystem. Much of the debate in this region 
on legislation to control acid deposition (and imple- 
mentation of current regulations for ozone and other 
pollutants) has focused on the scientific certainty 
linking the pollutants to forest damage. 
The Problem of Scientific Uncertainty 
The White House Office of Science and Tech- 
nology Policy addressed this problem in a report to 
the President in 1983. Several of the conclusions in 
their report are critical to considerations of the future 
of the fourth forest. 
1. "Recommendations based on imperfect data 
run the risk of being in error; recommendations for 
inaction pending collection of all the desirable data 
entail even greater risk of damage." 
(1) Paul W. Hansen is the acid rain project coordinator 
with the Izaak Walton League of America. 
2. "It is in the nature of the acid deposition prob- 
lem, that actions have to be taken despite incom- 
plete knowledge. . . . If we take the conservative 
point of view that we must wait until the scientific 
knowledge is definitive, the accumulated deposition 
and damaged environment may reach the point of 
‘irreversibility.’ " 
3. "We as a committee are especially concerned 
about possible deleterious effects of a sustained 
increase in the acidity of unmanaged soils. Its mi- 
croorganism population is particularly sensitive to a 
change in acidity. But it is just this bottom part of the 
biological cycle that is responsible for the recycling 
of nitrogen and carbon in the food chain. The proper 
functioning of the denitrifying microbes is a funda- 
mental requirement upon which the entire bio- 
sphere depends. The evidence that increased acid- 
ity is perturbing populations of microoganisms is 
scanty, but the prospect of such an occurrence is 
grave. It may take years of accumulation of acidity, 
from wet or dry deposition, before measurable con- 
sequences would be observed. Such an effect is 
‘long-term’ or ‘irreversible.' It may take at least that 
many years or longer for the soils to revert to their 
original condition. It is this possibility which provides 
us with the greatest concern." (On Camel's Hump in 
Vermont, where 50 percent of the red spruce have 
died or declined in the past 10 years, organic matter 
in the soil was found to have doubled or trebled, 
indicating that something was wrong with the forest 
soils' decomposing mechanism.) 
4. "We recommend that additional steps should 
be taken now which would result in meaningful re- 
ductions in the emissions of sulfur compounds into 
the atmosphere." 
Reduction below present sulfur dioxide emis- 
sion levels would reduce total sulfur deposition lev- 
els and as a consequence both reduce the proba- 
bility for major changes in additional acid sensitive 
lakes or forests and allow the possibility for a return 
toward the original biological conditions existing in 
recently acidified areas." 
133 
