Figure 8 The distribution
of relative ecosystem
sensitivity to acidic
deposition based upon
the soil buffering
characteristics
Acidification. Soil acidification occurs when base cations on the soil exchange
complex are replaced by hydrogen and/or aluminium. Base cations are supplied
by weathering and atmospheric deposition and removed by plant uptake and
leaching. Leaching of cations depends on leaching of mobile anions such as
SO
\ and NO
\. In many areas input and output of SO
\ are quite similar.
However, adsorption and/or plant uptake may occur. The nitrogen processes are
more complex. Atmospheric deposition includes both NO V
and NH
>; the latter
may give NO
\ and hydrogen ions through nitrification. Nitrogen-saturated
ecosystems (where nitrogen inputs are in excess of ecosystem nutrient needs,
such as seen in highly polluted parts of Europe) will leach a greater proportion of
nitrogen deposited than ecosystems where nitrogen is limiting vegetation growth.
In some areas, very little nitrate leaches at all. As bases leach from the soil, the
base saturation and pH may decrease (the soil acidifies) if the soil is not
sufficiently buffered by soil mineral weathering. The rate of acidification will
depend on the capacity of the base cation storage on the cation exchange
complex. Lake and stream water acidification occurs as the soils in the catchment
acidify and the decrease in pH, increases in aluminium concentrations and the
loss of fish have been the clearest and most severe impacts of acidic deposition,
particularly in the sensitive regions of Scandinavia, the UK and NE North
America. The soil acidification can itself have impacts on the vegetation at a site,
leading to losses in biodiversity and plant vigour. The widespread tree damage in
central Europe and parts of Canada and the USA have been attributed to ‘acid
rain’. The indications are that pollution is one of the main causes, but that the
situation relating to tree damage is the result of a complex interaction of different
pollutants with biotic and climatic stresses.
Kuylenstierna et al. have used soil buffering characteristics to map the
J. D. Aber, W. McDowell, K. Nadelhoffer, A. Magill, G. Berntson, M. Kamakea, S. McNulty, W.
Currie, L. Rustad and I. Fernandez, Nitrogen saturation in temperate forest ecosystems,
hypotheses revisited. BioScience, 1998, 48, 921—934.
A. Wellburn, Air Pollution and Acid Rain: The Biological Impact, Longman, Harlow, 1990.
J. C. I. Kuylenstierna, H. Rodhe, S. Cinderby and K. Hicks, Acidification in developing countries:
A Perspective on Global Air Pollution Problems
35
of relative ecosystem
sensitivity to acidic
deposition based upon
the soil buffering
characteristics
Acidification. Soil acidification occurs when base cations on the soil exchange
complex are replaced by hydrogen and/or aluminium. Base cations are supplied
by weathering and atmospheric deposition and removed by plant uptake and
leaching. Leaching of cations depends on leaching of mobile anions such as
SO
\ and NO
\. In many areas input and output of SO
\ are quite similar.
However, adsorption and/or plant uptake may occur. The nitrogen processes are
more complex. Atmospheric deposition includes both NO V
and NH
>; the latter
may give NO
\ and hydrogen ions through nitrification. Nitrogen-saturated
ecosystems (where nitrogen inputs are in excess of ecosystem nutrient needs,
such as seen in highly polluted parts of Europe) will leach a greater proportion of
nitrogen deposited than ecosystems where nitrogen is limiting vegetation growth.
In some areas, very little nitrate leaches at all. As bases leach from the soil, the
base saturation and pH may decrease (the soil acidifies) if the soil is not
sufficiently buffered by soil mineral weathering. The rate of acidification will
depend on the capacity of the base cation storage on the cation exchange
complex. Lake and stream water acidification occurs as the soils in the catchment
acidify and the decrease in pH, increases in aluminium concentrations and the
loss of fish have been the clearest and most severe impacts of acidic deposition,
particularly in the sensitive regions of Scandinavia, the UK and NE North
America. The soil acidification can itself have impacts on the vegetation at a site,
leading to losses in biodiversity and plant vigour. The widespread tree damage in
central Europe and parts of Canada and the USA have been attributed to ‘acid
rain’. The indications are that pollution is one of the main causes, but that the
situation relating to tree damage is the result of a complex interaction of different
pollutants with biotic and climatic stresses.
Kuylenstierna et al. have used soil buffering characteristics to map the
J. D. Aber, W. McDowell, K. Nadelhoffer, A. Magill, G. Berntson, M. Kamakea, S. McNulty, W.
Currie, L. Rustad and I. Fernandez, Nitrogen saturation in temperate forest ecosystems,
hypotheses revisited. BioScience, 1998, 48, 921—934.
A. Wellburn, Air Pollution and Acid Rain: The Biological Impact, Longman, Harlow, 1990.
J. C. I. Kuylenstierna, H. Rodhe, S. Cinderby and K. Hicks, Acidification in developing countries:
A Perspective on Global Air Pollution Problems
35