Ecological Risk Assessment of Diffuse and Local Soil Contamination Using Species Sensitivity Distributions - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 630

pollution. One example is shown here, to illustrate the real suite of responses that
may occur in an exposure situation. We consider this example key for understanding
the remainder of the chapter.
Figure 14.2 shows which simultaneous responses to contaminant exposure may
occur in soils. Responses are expressed as numbers of biological taxa and as activity
parameters, respectively, along a copper (+ cadmium + zinc + lead) contamination
soil gradient near a metal smelter in Sweden, a situation with limited influences
of other stressors (Tyler 1984 ). Note that the graph depicts response functions in
relation to total metal concentrations, while it is likely that only part of the total
concentration is available for uptake due to ageing and sorption processes. Due to
the relative homogeneity of the gradient soils with respect to metal binding proper-
ties, we expect that the response graphs would show similar patterns when they are
expressed on the basis of metal concentrations available for uptake in the different
species.
As illustrated in the figure, risk modeling using distributions of sensitivities may
focus on two types of impacts, i.e., structural and functional impacts (the latter relat-
ing to the concept of Ecosystem Services). When present in high concentrations, one
or more contaminants might impact one or more of the species that make up the vital
soil. These contaminants may thereby affect the structural integrity of the species
assemblage in the soil system. Some species are decreasing in abundance (until they
are lost), while others (opportunistic species) flourish, until they are also affected at
higher concentrations. The increase of such species at moderate exposures may be

160%

microfungi
macrofungi
vascular plants
mosses
Cladonia
other lichens
lumbricids
Fungal biomass (km/g)
Decomposition rate (mg/g.d)
Phosphatase activity (mmol/dm3)
N.mineralisation (mmol/dm3)
Series12

140%

120%

100%

80%

60%

40%

20%

0%

10 100 1000 10000 100000

Cu µg/g (+ correlated Cd, Zn and Pb)

Fig. 14.2 Biotic responses as functions of copper concentration along a multiple metal gradient
in the field, recalculated to 100% performance of each of the variables at the clean end of the gra-
dient ( broken horizontal line ). This figure illustrates the application of the sensitivity distribution
approach to various ecological impacts in contaminated soils. Both structural ( black )and func-
tional ( white ) aspects of the vital soil system change when contaminant concentrations increase.
Note the opportunistic increase of some parameters (e.g., macro- and microfungi) at intermedi-
ate concentrations. The graph is redrawn from the data of Tyler ( 1984 ) for a metal smelter in a
homogeneous forested area