Environmental Engineering Reference
In-Depth Information
a consequence of (relatively) low sensitivity in combination with changed ecolog-
ical interactions. For example, a prey species may increase in abundance when its
more sensitive predator declines. Simultaneously, some of the key
functional char-
acteristics
of the soil system may be affected. When species decrease or increase in
abundance, their contributions to the cycling of nutrients and energy also change.
This eventually shows up as functional changes.
It has been demonstrated frequently that structural changes precede functional
changes, especially when functional changes are considered at the level of changes
in the overarching Ecosystem Services of the soil (like decomposition efficiency),
and not on a basic functional response like a change in activity of a single enzyme.
In other words: it can be assumed, based on available evidence, that sufficient pro-
tection of structure also would imply sufficient protection of Ecosystem Services, so
that Risk Assessments could focus on the former. If one doubts this assumption, one
can consider both types of effects, and appraise the soil by using the most appropri-
ate or most sensitive endpoint. In the Netherlands, protective soil quality standards
are derived in this way: preliminary standards are derived for both structure and
function, and the most sensitive endpoint is used to set the regulatory standard (that
then aims to protect both).
14.2.4 From Field Effects to SSD Modeling
Each species and each functional trait seems to respond in a typical way to con-
taminant exposure, and the responses also depend on the contaminant, the site
characteristics and the other parts of the community. Given the vast variety of impact
types and magnitudes, it seems hardly possible to define scientifically sound ways
to derive an appraisal method that can be used in daily practice for protecting and
managing vital soils threatened by contaminants. Nonetheless, instead of focusing
on the apparent difficulties, one can focus on the very fact that “
All animals are
unequal
” in their sensitivity to contaminants (Fig.
14.2
), and that this variation per
se might be a good basis for Risk Assessment. As eloquently stated:
Variability is 'noise' for physicists, but variation is the key issue of the research of
ecologists, for them, variation is 'music' (Joosse-van Damme
1984
).
Instead of considering this variety as a nuisance, it is the dissimilarity in response
patterns that is a valuable key fact of life:
without variability, all species would be
killed at a specific concentration of a contaminant in their environment
! And it is
this “music” that was recognized in the mid-eighties of the last century as a key
option for appraisal and protection of biotic communities. As a result, sensitivity
distribution modeling was triggered.
On both sides of the Atlantic Ocean, in the United States of America and Europe,
scientists developed the modeling concept of SSDs. Key inventors were Klapow and
Lewis (
1979
) for California, and especially Hansen, Mount and others for the federal
U.S. government (U.S.EPA
1978a
,
b
), and Kooijman (
1987
) and Van Straalen and
Search WWH ::
Custom Search