Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 125

25

Fig. 2.14 Yearly increase
rate of the urban area in
Nanjing and Suzhou, China
(Zhang et al. 2005 , 2006 )

20

15

Nanjing
Suzhou

%

10

5

0

1984-1995 1995-2000 2000-2003

A considerable portion of the deposited soils are sealed for building or
road construction purposes. The expansion of city areas connected with land
consumption , and consequently with losses of natural soils, is a well-known phe-
nomenon. In the developing countries like China and India, these tendencies have
reached spectacular dimensions. The development may continue in the next decades,
since the degree of urbanization (people living in agglomerations with more than
150,000 inhabitants) has only achieved 43% in China, while in industrialized coun-
tries the values can be 92% (United Kingdom), 80% (USA), and 81% (Japan).
Generally speaking, the development in the Chinese big cities such as Nanjing and
Suzhou is faster than we have ever seen before (Fig. 2.14 ). The losses of soils do
not include only less fertile soils with shallowness and high stoniness, fertile soils
are involved as well. In Nanjing 14.5% of fertile agriculturally used soils (Argosols,
Cambisols) were sealed, while the anthropogenically changed Anthrosols occupy
6.8% only (Zhang et al. 2005 , 2006 ).
Apart from the completely sealed areas, deposited soils between buildings (usu-
ally used as lawns or small parks) show physically damaged soil structure , caused
by soil handling. After deposited soils are placed, the normal organic matter cycle
is interrupted (litter raked or swept away, only individual or groups of plants are
cultivated, reduced biological activity) leading to a constrained vegetation cover. In
turn, this tends to surface crusting (thin layer of washed-in particles), reduced water
infiltration, and accelerated erosion (rill, gully) along anthropogenically overused
lines like pedestrian foot paths, especially in parks, playgrounds, and sports fields
(Craul 1992 ). The reason for enhanced wind erosion in areas where construction
activity occurs is removal of vegetation, excavation and unprotected stockpiling of
different materials. Deposits and removal of vegetation are combined with a high
percentage of bare soils. Specific indicator species such as Artemisia vulgaris and
Solidago canadensis living in such conditions can be found. Also specific indicator
plants that have a high tolerance to heavy metals are of importance in relation to spe-
cial deposits like ore deposits, where species tolerant to heavy metals (for example
Festuca ovina , Silene vulgaris , Agrostis tenuis ) can grow (Genske 2003 ).
Moreover, problematical physical impacts have to be considered in subsur-
face mining areas, some kinds of quarries, and pumping facilities of oil and gas.