Contribution of ecology to ecotoxicological risk
assessment
In higher-tier risk assessment procedures ecological
expertise is highly needed, particularly for perform-
ing and interpretingmodel ecosystemexperiments and
field tests. First, temporal and spatial variability be-
tween ecosystems is large. So, it needs to be evaluated
whether individual model ecosystem experiments are
representative for the aquatic ecosystem potentially at
risk. Secondly, studies at higher levels of biological or-
ganisation usually result in complex data sets on e.g.,
densities of various taxa identified in both treated and
control systems. Consequently, specialised techniques
are needed to determine cause-effect relationships be-
tween pesticide concentrations and changes observed
at the community- and ecosystem-level. An exam-
ple of a recently developed multivariate technique to
describe the impact of chemical-stress at the commu-
nity level is by Van den Brink & Ter Braak (1998).
Finally, for performing (semi-)field tests in a cost-
effective way for administrative purposes, knowledge
on sensitive indicators of pesticide-stress is essential.
Ideally, these indicators should be ecologically signif-
icant, rapid and non-destructive, such as the technique
described by Snel et al. (1998). This technique, by
measuring the efficiency of photosystem II electron
flow using chlorophyll fluorescence, is a convenient
method to indicate herbicide-stress.
Contemporary ecological theory is to date poorly
developed in higher-tier risk assessment of pesticides
(Maund et al., 1997). Nevertheless, the ecological
dimension in these advanced procedures certainly can-
not be ignored if the aim is to protect aquatic popula-
tions and communities fromunacceptable side-effects.
To value responses observed in mesocosms or field
monitoring programmes, ecological knowledge has to
be incorporated on life-cycle characteristics and eco-
logical strategies of sensitive aquatic species. This
type of information, combined with that on the extent
of isolation of the system subject to stress, is a pre-
requisite to shed light on recovery potential and the