Page 65 - Soil and water contamination, 2nd edition

52 Soil and Water Contamination
6642 Water vapour in Snow and ice
atmosphere 29 million km 3
3
13,000 km
Precipitation Precipitation
3
3
385,000 km /y 111,000 km /y
Evapotranspiration
3
Evaporation 71,000 km /y
3
425,000 km /y
Rivers and lakes
200,000 km 3
Groundwater 3
Seas and oceans
3 8.0 million km
1,348 million km

Figure 3.1 The hydrological cycle (pools and fluxes after Winter et al., 1999)

book, the discussion on the environmental compartments in this chapter and in part IV of
this book is restricted to soil, groundwater, and surface water. This chapter focuses on the
physical and chemical characteristics of these environmental compartments and the main
sources of pollution in them.

3.2 SOIL

3.2.1 Definition of soil

According to the US Department of Agriculture (USDA, 1999), soil is the collective term for a
natural body comprised of solids (minerals and organic matter ), liquid, and gases that occurs
on the land surface, occupies space, and is characterised by one or both of the following:
horizons, or layers, that are distinguishable from the initial material as a result of additions,
losses, transfers, and transformations of energy and matter or the ability to support rooted
plants in a natural environment. The upper limit of soil is the boundary between soil and
air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are
not considered to have soil if the surface is permanently covered by water too deep (typically
more than 2.5 meters) for the growth of rooted plants. The lower boundary that separates
soil from the non-soil underneath is most difficult to define. Soil consists of horizons near
the Earth’s surface that, in contrast to the underlying parent material, have been altered by
the interactions of climate, relief, and living organisms over time. Commonly, soil grades at
its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or

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