Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 232

and Naoshima islands, with cleanup costs estimated to be in the order of 30 billion yen
(approximately $300 million).
7.3.6 Greenhouse Gases
Activities associated with urban living contribute signiicantly to the production of green-
house gases. The combustion of fossil fuels is a major source of carbon dioxide production.
Wood burning is another signiicant source. Methane released from anaerobic decomposi-
tion of organic waste in dumps and other sources contributes about 15% of the greenhouse
effect. Chloroluorocarbons (CFCs), used as refrigerants in air conditioners and as pro-
pellants, were produced in the 1950s. Their use has decreased signiicantly in developed
countries, with the exception of developing countries, after the introduction of measures
for their reduction. Concentrations of ozone, produced in internal combustion engines,
have also increased. Levels have tripled in Europe and North America in the troposphere.
The evidence indicates that human activities during urbanization have clearly increased
these levels (greenhouse gases and CFCs), and that it is very likely that these will affect the
geoenvironment in the future. If global warming happens, sea levels will rise as a result of
ice cap melting and looding of coastal regions will occur. This will disrupt coastal ecosys-
tems and habitats. Permafrost melting will impact arctic ecosystems and will also cause
considerable distress to physical structures because of terrain instabilities.
7.3.7 Impact on Ecosystem Biodiversity
The multitude of microorganisms and their diversity in the soil ecosystem is essential in
maintaining and developing a healthy soil. Organic matter and nutrient recycling, min-
eralization, and decomposition are essential processes that have not been studied exten-
sively in urban soils, particularly when compared with agricultural soils (Harris, 1990).
Soil organisms include microbiota (bacteria, fungi, algae, protozoa), mesobiota (arthro-
pods, nematodes, springtails, etc.), and macrobiota (earthworms, mollusc, larger arthro-
pods, enchytraeids, etc.).
The impact of urbanization on soil properties and attributes includes great variability,
compaction, bare top soil that is often water repellent, altered pH conditions, restricted
aeration and drainage, altered nutrient cycling of the soil organisms, presence of other
materials and contaminants in the soil, and altered temperature proiles (Craul, 1985). All
these changes signiicantly impact on soil organisms. For example, trampling by humans
in urban forests can signiicantly reduce the numbers of earthworms. More information
is needed, however, on species diversity and numbers in urban soils and the impact of
recreation, disturbance, compaction and contamination on these numbers. This microbial
community can be used as an indicator of soil quality.
Chemicals from wastes, leaks, and emissions enter the soil ecosystem. They can accu-
mulate in organisms via bioaccumulation as higher animals on the food chain eat lower
contaminated organisms. As the contaminants increase in the species, the species may
become compromised, causing an imbalance in the whole system. Anecdotal evidence
indicates that fewer organisms, less biomass, and fewer species of organisms are found in
urban soils. Assuming the evidence to be valid, this would be an indication of the stress
on these organisms caused by the impact of human activities on urban soils. Although
direct measures of the level of degradation or impairment of the quality of urban soils are
not available, an argument could be made in support of the use of sensitive soil fauna and
microlora as indicators for urban soil quality.