Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 101

• Acidic, strong leaching environment : The ultimate end products formed after pro-

longed weathering include kaolinite clay, alumina (bauxite) and iron hydroxides
and oxides.

Weathering, leaching, pH and internal (within soil profile) translocation in all
three environments affect also the distribution and mobility of those chemical
elements such as cadmium and lead that are recognised as contaminants, regardless
of whether they were native or have been added by mankind.
Most of Northern and Western Europe are in the third class of environments
( acidic, strong leaching environment) . But they still have youthful landscapes and
soils, as they are post-Glacial and rainfall is sufficient to bring about leaching and
soil pH will be lower than 6, unless the parent lithology is calcareous or the soils
have been amended by concrete, mortar or other technogenic materials. Southern
Europe is characterised by weak leaching environments, and, where erosion and
sedimentation is active, by youthful landscapes also. The environments of China,
Canada and much of the United States of America occupy all three classes, and on
the whole may also be interpreted as youthful landscapes due to active erosion.
The Australian continent has examples of weathering environments that origi-
nally were acidic and strongly leaching, but due to their ancient origin and changed
climate are now confined or weakly leaching, thus preserving characteristics that
belong to the distant past. It also contains strongly alkaline confined environments.
On a much more detailed scale, the Holocene soils of the Netherlands, which are
largely alluvial and glacial terminal morainic sediments and peat deposits, have been
subdivided into four broad soil categories in order to understand the characteristic
trace element background concentrations. They have been found to display specific
geochemical affinities.
Figure 2.4 showing the generalised soil map of the Netherlands may be compared
to the generalised soil map of the area around Melbourne, Victoria, Australia, in
Fig. 2.5 .
The soils around Melbourne are mapped on the basis of underlying geological
parent materials, with an overlay of weathering history and soil development, i.e. ,
soil age, and represent local regoliths. Thus, the red loams and the brown loams over
clay are ancient well-leached, acidic deep soils. They were formed on Pliocene-
Eocene basalts during a former wet and warm climate, and where the present
climatic regime produces some 850 mm yr − 1 rainfall and 1,060 mm yr − 1 evapo-
ration, with the main rainfall occurring during the colder winter months. Thus the
weathering and soil formation goes back to the early Pleistocene at the least.
In the far west of the Melbourne map, the heavy clays on Quaternary basalt
all have strongly alkaline and sodic sub-soils with lime accumulations at 0.5 m or
deeper, because there can be no significant leaching with an annual evaporation of
more than 1,600 mm and annual rainfall of 550 mm.
Deep sands free of lime are Pleistocene windblown highly leached and acidic
sand sheets with podzol profiles, while the deep sands with lime are young Holocene
calcareous dunes, whose carbonate content derives from seashells.