Introduction to Ecological Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 579

as it is experienced, certainly in rural areas and nature reserves, but also in urban
areas and even in big cities, in parks and even in busy streets lined with trees.
Ironically, the general public is not always aware of the fact that above-ground biol-
ogy would not have much of a chance without the amazing activities of enormous
numbers of organisms in the soil, and that lie underneath the soil surface.
In conclusion, scientists such as eco(toxico)logists, biologists and soil scientists
have the serious duty of communicating the blessings of soil ecology to decision-
makers, regulators and consultants. Teachers and scientific journalists can play an
important role in communicating the assets of soil ecology to the general public.
13.2 Soil Biology
13.2.1 Soil Life
Millions of millions of organisms live in each handful of soil, differing widely in
appearance and behaviour. These organisms include bacteria, algae, fungi, proto-
zoa, and larger and more complex organisms, such as nematodes, micro-arthropods,
potworms, earthworms, insects, small vertebrates, and (the roots of) plants. These
soil organisms live in an extremely complex mutual interaction, and likewise in
complex interactions with their physical and chemical environment.
The activity in soils is impressive. In an arable soil in Western Europe, the micro-
bial community decomposes about 5,000 kg of carbon per hectare and per year, and
100 kg of nitrogen (N) per hectare and per year (Bloem and Breure 2003 ). Soil
organisms perform an extremely wide range of processes which mainly serve the
food supply of the organisms. Given the complexity of the mutual interactions of
organisms in soil, and their interactions with the physical and chemical environment,
it is nearly impossible to comprehend, let alone describe, the complete functioning
of the whole ecosystem.
A relatively simple way to illustrate interactions between organisms in soil is by
the food web, that is, a diagram that illustrates the feeding relationships between
organisms. For a simplified example, see Fig. 13.2 (Ingham 2000a ).
13.2.2 Classification of Organisms
13.2.2.1 Types of Classification
Since so many types of organisms occupy the soil, a classification of these organ-
isms is essential. Because of the enormous diversity of soil organisms, several
criteria for classification can be used and several classifications do exist. For exam-
ple, the ecosystem can be subdivided into several functional groups, which are
each responsible for a specific function, for example, protein-degrading bacteria, or
humus-degrading actinomycetes. Alternatively, soil organisms can be categorized
into different classes, according to size: