Introduction to Ecological Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 617

of the activities of soil organisms. These measurements can be on the sub-cellular
level (DNA, proteins), cellular level (activity of cellular processes), or on the level
of species (determination of presence, absence and abundance of species), popula-
tions or communities (diversity and composition of groups of species). There has
been a lot of debate on the relationship between the numbers of organisms and the
quality of Ecosystem Services or Ecosystem Health. In point of fact, no univer-
sally accepted indicators exist that represent the quality of Ecosystem Services or
Ecosystem Health.
Many techniques exist and are also in the process of standardisation in
NEN (Dutch Standardisation Institute) and ISO (International Organization for
Standardization), but application in a monitoring network is complex and expen-
sive. In site-specific Risk Assessment, especially, these techniques are being applied,
however.
One popular criterion for Ecosystem Health is a description of the community
composition in comparison with the composition of a reference community. To
assess the impact of contaminants on the soil ecosystem, this reference community
could be a similar ecosystem under comparable conditions as at the contaminated
site, but without the contamination. Although this criterion certainly has a certain
relationship with Ecosystem Health, it was concluded in Section 13.5.1 , however,
that the unimpaired condition in which ecosystems show no influence from human
activities (Ecological Integrity) is not necessarily the optimal condition for the soil
ecosystem.
It is important to note that the principle of monitoring of Ecological Health is
dependent on the size and complexity of the species (Beck et al. 2005 ). Generally,
indicators related to microorganisms focus on functions such as respiration, or activ-
ity. Indicators for higher organisms, however, usually relate to the structure of the
community instead of functions. One important line of research for the future will
be the coupling of ecosystem structure and functioning (Breure et al. 2008 ).
Rutgers et al. ( 2008 ) derived ten references for good biological soil quality. The
references are specific to ten combinations of land use (e.g., dairy farms, arable
fields and headlands) and soil type (sand, peat, clay and loess).
13.9.4 Biological Classification Systems
Some guidebooks indirectly refer to the presence of a healthy soil ecosystem, for
example, by the criterion that it 'has a rich, earthy smell', the unmistakable proof
of the metabolisms of an almost inconceivable number of soil organisms. Some
quick evaluations of Soil Health refer to biological aspects such as the presence of
earthworms, the earthy smell, and the loose, crumbly structure of the soil (Bowman
1994 ).
In Europe, several indicator systems have been developed. In Denmark,
for example, seven different characteristics for Soil Health are considered.
Subsequently, these characteristics are coupled with Ecosystem Services-related soil
ecological parameters and microbial indicators (National Environmental Research