(Acidic deposition and the environment) Page: 4 of 15
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terrestrial and aquatic systems. With respect to the last topic, it was
found that the behavior of sulfur in soils is fairly well understood and
can be predicted with some degree of certainty, whereas the lack of
predictability concerning nitrogen dynamics in forest soils makes critical
load assessments extremely uncertain. Consequently, most critical load
presentations focused primarily on the impact of atmospheric sulfur
deposition. Numerous presentations documented various degrees of nitrogen
saturation (i.e., incomplete retention of atmospheric nitrogen) in forest
ecosystems and the effect of excess nitrogen on nutrient deficiencies and
aluminum toxicity in trees, as well as the effect on drainage water
It was interesting to note the strong emphasis on nitrogen in the
"post-acid deposition" research in Europe, both through modeling efforts
and field experimentation. The NITREX project, sponsored by the
Commission of European Communities (CEC), stands prominently among those
efforts. The program establishes a network of sites in Norway, Sweden,
The Netherlands, Denmark, Germany, and the United Kingdom, spanning a
gradient from low to high atmospheric nitrogen deposition. It aims at
experimentally altering the nitrogen input to entire catchments and/or
large forest stands to determine whether increased nitrogen deposition
will lead to nitrogen saturation, the effect of nitrogen saturation on
biogeochemical fluxes, and the extent to which this condition can be
reversed under proposed lower nitrogen deposition scenarios. Some of the
same sites and institutions are also cooperating under the CLIMEX program,
which will focus on the ecosystem response (particularly plant-soil-water
linkages and processes) to climate change.
Several papers at the conference sessions dealt with analysis of
throughfall and its potential use in deposition studies. British
scientists reported new results of 35S studies originally performed at
ORNL and recently repeated in Europe. Results were similar, with the
authors concluding that labeled internal sulfur contributed a small
percentage to the summer flux of sulfate in throughfall at the Devilla
Forest in Scotland. This finding confirms that sulfate in throughfall is
largely deposited from the atmosphere. The authors improved on the ORNL
studies by adding the 35S to th, scil system but still felt that further
improvements could be made and that the possibility rf non-steady-state
behavior of 35S in forest systems must be considered in interpreting the
data. Whole-catchment manipulation studies are planned in Sweden to study
the behavior of applied 35S in throughfall and stream export and to
determine their utility in deposition estimates. Recent catchment studies
indicated excellent agreement between long-term estimates of sulfate
fluxes in throughfall and stream export. These studies indicate
substantially higher deposition rates of sulfur to forests than do several
deposition models, thereby creating considerable disagreement between the
meteorological and modeling communities and researchers in biogeochemical
cycling who have applied throughfasl methods. Several different studies
using a variety of methods (exclusion chambers, fumigations with SO2 and
NO., and plot and catchment manipulations with sulfate salts and elemental
sulfur) all confirmed minimal internal leaching of foliar sulfur and the
dominant role of deposition in throughfall sulfate. Results of studies
on nitrogen compounds are still contradictory but suggest important foliar
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Garten, C. T.; Lindberg, S. E. & Van Miegroet, H. (Acidic deposition and the environment), report, October 24, 1990; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1207839/m1/4/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.