Environmental Engineering Reference
In-Depth Information
this rough work. Those macromolecules which are too big to be taken up by microbial
cells are split into smaller molecules by their exoenzymes, which act out of the cells
which produce them. At the end the molecules small enough are utilized within the
microbial cell for extracting the energy from the chemical bonds of these reduced
substrates and synthesize new molecules from the building blocks.
Depending on the ratio of organic litter to soil-living microorganisms, some part of
the organic matter will not be degraded or only partly degraded. This residual organic
matter has a constant level in a well-balanced soil from year to year, constituting the
humus content of the soil. When the activity of the soil microbes is low, mineralization
is slow and more organic matter will form humus. When microbes are very active
(tropics), all of the organic matter will be mineralized beside energy production, and
consequently, the soil grows poor in humus.
Humus is formed from the relative stabile residual molecules of the biodegra-
dation process after demethylation, decarboxylation, beta-oxidation of the hardly
biodegradable lignins, tannins, polyphenolic substances. Further transformation into
humus molecules is achieved mainly by physico-chemical processes, such as autooxida-
tion, nucleophilic addition, condensation, or polymerization from the stable residual
compounds of the mineralization.
The number of soil microorganisms increases when enough energy substrate is
present—litter full of reduced organic molecules, such as carbohydrates (sugars, starch
and cellulose), pectins, proteins, etc.—and decreases when energy substrate runs out.
During the period of bacterial growth, the rate of biosynthesis is high and many of the
biogenic elements built into the cells (e.g., N) will be available to plants only after the
death of these microorganisms.
Soil health or damage can be monitored by genetic, metabolic (enzymatic activ-
ities of soil biota hydrolyzing detritus) and physiological markers. Damage to soil
microorganisms, plants and animals is another useful indicator. Any function of the
soil machinery such as the mineralization of organic matter including nonhydrolyzable
organic matter and xenobiotics are measurable indicators for the characterization of
soils' health status and activity. Many of the more complicated autoecological and
synecological markers including changes on population dynamics, species diversity,
yield reduction in the case of cultivated plants, and forest or the energy transfer and
the food chain structure may characterize the soil ecosystem properly.
3 ECOSYSTEM AND MAN: ECOSYSTEM SERVICES
Biodiversity, through the provision of ecosystem goods and services, provides the basis
for all life on earth. It supports the economic and social development and is vital to
human health and well-being. Species of microorganisms, plants, fungi, and animals
are the sources of food, fuels, medicines, clothing, and building materials. The com-
plexity of the ecosystem provides clean water, healthy soil, and clean air. The loss of
ecosystem goods and services is the barrier of human health and well-being.
Ecosystem services are classified into four main groups. The main services are
defined by TEEB (2010) as the outcome of The Economics of Ecosystems and
Biodiversity Project. The study is a major international initiative to draw attention
to the global economic benefits of biodiversity, to highlight the growing costs of
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