World’s Soil Resources

Prepared by P. Reich
Figure 4.9 Use of different Technosols derived from wastes in the recovery of hyperacid soils and waters in the restored mine of Touro
(Galicia, NW Spain).
4.4 | Atmospheric deposition
4.4.1 | Atmospheric deposition
The impacts of the deposition of atmospheric pollutants on soils vary with respect to soil sensitivity to
a specific pollutant and to the total pollutant load. Anthropogenic emissions of sulphur, nitrogen and trace
elements to the atmosphere mainly derive from fossil fuel and waste combustion in, for example, power
generation, incineration, industry and transport. Emissions may also derive from non-combustion processes
such as agricultural fertilizers or waste amendments. Mining activities may also contribute, for example
Hg mining. Once in the atmosphere, these pollutants can be transported off-site and even cross national
borders before being deposited either as dry or wet deposition. Deposition is more accentuated in forests,
especially in coniferous forests (because of reduced wind speeds) and in areas of high elevation because of high
precipitation rates.
Once in the soil, pollutants can be mobilised by being: (i) released back to the atmosphere; (ii) made available
to biota; (iii) leached out to surface waters; or (iv) transported to other areas by soil erosion. Pollutants disrupt
natural biogeochemical cycles by altering soil functions. This disruption may come about through direct
changes to the nutrient status, acidity, and bioavailability of toxic substances, or through indirect changes
to soil biodiversity, plant uptake and litter inputs. Soil sensitivity to atmospheric pollution varies with respect
to: (i) key properties influenced by geology and associated pedogenesis such as cation exchange capacity,
soil base saturation, aluminium, or rate of base cation supply by mineral weathering); (ii) organic matter
content and carbon to nitrogen ratio (C:N); and (iii) position of the water table. When atmospheric pollution
is associated with sulphate deposition, the capacity of soils to adsorb sulphate (e.g. soils with a dominance
of short-range ordered constituents) plays a key role in buffering the acidification process (Camps Arbestain,
Barreal and Macías, 1999; Rodríguez-Lado, Montanarella and Macías, 2007). Harmful effects on soil function
and structure occur where deposition exceeds the ‘critical load’ - the specific amount of one or more pollutants
that a particular soil can buffer (Nilsson and Grennfelt, 1988). Estimates and mapping of critical loads of acidity
Status of the World’s Soil Resources | Main Report Soils and Humans
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