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Box 1 -
Soils in the urban environment
Urban and sub-urban soils are an essential part of the urban ecosystem that contributes, directly or
indirectly, to the good quality of citizens' lives. The urban green infrastructures are dependent on a
"Brown infrastructure" (sensu Pouyat et al., 2010) composed of highly diversified soils. The major
part of these soils (Anthropogenic Soils), derive from extremely variable human actions. In the
urban environment, man represents the main pedogenetic factor.
In the urban environment the typical habitat fragmentation and the wide spectrum of land use
determines, in fact, a strong variation of the chemical / physical / biological soil features. A mosaic
ranging from natural or seminatural soils (eg. Historic mansions, urban parks, urban and peri-urban
protected areas, peripheral agricultural areas), to deeply altered soils, soils covered by
impervious/semipervious surfaces until to new soils (eg. former industrial areas, embankments,
flower box).
These soils, even if their functions are extremely limited, provide the same ecosystem services of
natural soils: reducing the amount of pollutants, providing organic carbon stock and mineral
nutrients, improving aesthetic, recreational, cultural functions of green areas and biodiversity
preservation.
Despite their peculiarities, such soils continue, with functionality depending of alteration degree, to
provide the same ecosystem services of natural soils. Mitigate the effects of pollutants, providing
organic carbon stock and mineral nutrients, regulate the hydrological cycle, improving aesthetic,
recreational, cultural functions of green areas and biodiversity preservation.
Soil functions are, however, totally lost with its removal, or greatly limited by sealing or high
pollution levels. The latter is of particular interest considering the proximity of the population and
the progressive growth of the urban and peri-urban horticulture.
Soil functions and ecosystem services
Healthy soil performs ecological, environmental, economic, social and cultural functions such as
sequestering CO
2
, mitigating stormwater runoff, supporting plant life, and sustaining the microbial
populations that form the basis for all living things.
The
seven major soil functions
are as follows:
−
Biomass production
:
soil provides food, fodder, renewable energy and raw materials. Food and
other agriculture production, essential for human survival, forestry and almost all vegetation
are totally dependent on soil.
−
Storing, filtering and transforming nutrients, substances and water
:
Soil plays a crucial
protective function to mitigate and prevent the passage of pollutants into groundwater and the
food chain. The soils protective value depends on the physical- chemical properties, and by
biological activity that allows decomposition of the substances placed in the soil. Through its
ability to store large amounts of water plays an important role in prevent or reduce flooding.
−
Acting as carbon pool
: Carbon stored in
soils
represents the
largest terrestrial carbon pool
.
Soils can play a key role in
climate change mitigation through carbon sequestration and
greenhouse gases (
N
2
O
and
CH
4
) emissions regulation
−
Biodiversity pool, such as habitats, species and genes
:
soils are a reservoir of biodiversity.
They provide habitat for thousands of species regulating for instance pest control or the
disposal of wastes,
−
Physical and cultural environment for humans and human activities
:
soils provide physical
support to plants, animals and human infrastructures,
−
Source of raw materials
:
soils can be a source of materials like peat and clay
.
−
Archive of geological and archeological heritage
: Soils are the archive of our history and
culture. Archeological artifacts are stored in soils. A soil profile can tell a complete story of the
events that have been shaping the landscape in that site, in historical as well as in geological
times.
Soils provide
an array of
ecosystem services
(benefits people obtain from the soil) essential for the
environment and human well-being (Table 1).
Nonetheless, owing to unsustainable land uses, soil is degrading by erosion, loss of organic matter,
salinization/alkalinization, compaction, sealing, contamination, compromising the maintenance of
further productivity until the ultimate soil degradation phase, the desertification (Figure 1)