Landscapes have usually been assumed
to act merely as net sinks for acid
rain (1), but generation of acidity in soils
has recently been recognized as an additional
source. This is evident in reports
of the Norwegian project on "Acid Precipitation-Effects
on Forests and Fish"
(the SNSF project), for example (2-4).
However, acid rain is still considered
principally responsible for regional acidification
(2-4), because the increased flux
of s042- in rain is thought to result in
equivalent leaching of hydrogen ions and
other cations. We believe that this assessment
needs reexamination. Large
amounts of humic acids are present in
forested landscapes thought to be particularly
sensitive to acid rain. The solubility
of these humic acids is controlled by