ATMOSPHERIC SULFUR AND ITS LINKS TO THE BIOTA 181 



Likens: One important interface between the carbon and sulfur cycles is 

 shown by the problem of acidity of precipitation. Currently, the pH of 

 precipitation in the northeastern United States averages about 4 and appears to 

 be linked to pollution of air by gaseous forms of sulfur and nitrogen, which are 

 produced from combustion of fossil fuels. In November of 1964 the National 

 Center for Atmospheric Research measured values as low as pH 2.0 in parts of 

 the Northeast. Such acid rain and snow may have insidious effects on plant 

 productivity, but we know very little about this at present. In laboratory 

 experiments, Dr. C. C. Gordon has found that long-needle conifer species, such 

 as white pine, produce dwarfed needles when solutions of sulfuric acid at pH 

 <3.5 are applied by dropper to the emerging needles. When the solution is 

 applied as a mist, pH's <4.0 result in needles that grow to only half the length of 

 control needles. This so-called "short— long needle syndrome" apparently is 

 prevalent in conifers of the Northeast, where pH values of this magnitude are 

 now common, particularly during summer. 



Hill: Our precipitation may well have been quite acid in the Northeast for 

 the past 15 years; and we may be seeing the tail end of any short-term effects on 

 soils. However, it would appear that currently there is no accelerated weathering 

 of soils in the Northeast due to the increased acidity of precipitation. 



Woodwell: Dr. Hill, would you care to comment on the effects of acid 

 precipitation? 



Hill: In the report that I referred to, which is my chief source of 

 information on this subject, there was reference to some studies that had been 

 done in situations in which it was possible to correlate changes in growth rate as 

 measured by diameter of trees with calcium in the soil, and the indication was 

 that reduction in productivity of the order of possibly 1% per year might be 

 anticipated. They were very careful to say that this is a very difficult association 

 to make, and I do not believe they were necessarily conclusive on this point. 

 They thought that, in view of the risks involved and regardless of whether they 

 could be conclusive, it was worthwhile to make a strenuous recommendation 

 against further increases in S0 2 emission and, in fact, asked for reductions in 

 emission. 



