English Abstract In this report a strategy for ecological standard
setting is proposed for environmental variables in the field of
acidification, eutrophication and desiccation, using a risk assessment.
Risks at the species level and ecosystem level are specified. At the
species level the risks are assessed on the base of the ecological amplitude
of a species. The ecological amplitude describes the occurrence probability
of a species as a function of environmental variables. Values of the
environmental variable are assessed that correspond with a specified reduced
occurrence probability. Reduced occurrence probability may be due to
intoxication (too much) and limitation (too little). These values are
quantified for each species as the uppervalue and lowervalue of the
environmental variable that envisage 90% of the observations of a species
(5% percentile and 95% percentile values). At the ecosystem level risks are
specified as the concentration that protects a specified percentages of all
species. In the dutch environmental policy for pollutants this percentages
is set at 95%. The ecological standard is assessed by combining the risks
at the species level and the ecosystem level. The number of species, for
which the 5% and 95% percentiles are not exceeded, are plotted as a function
of the environmental variable. From this relation the maximum environmental
level can be assessed that protects 95% of all species. This strategy for
standards setting is illustrated with a case study in the Province of
South-Holland. Ecological standards are calculated for nitrogen load and
changes in groundwaterlevel using data on 285 plant species. This report
will be issued in english.
