GIS Based Chemical Fate Modeling: Principles and Applications

Chapter 20

Chemical Fate and Transport Indicators and the Modeling of Contamination Patterns

20.1 The Relative Risk Model

In the relative risk model (RRM) that we briefly mentioned in Chapter 17, Landis and Wiegers [1] show how ecological risk may be characterized in a semiquantitative form by identifying appropriate conceptual and spatial relationships between sources of contamination, habitats, and the stressors likely generated by the former and acting on the latter. These authors remark that the quantitative description of ecological effects is extremely complex; risk assessment requires on the one hand an explicit account of the complexity of ecological impacts, and on the other hand their tractable representation, overly complex and oversimplified approaches being both deceptive. In their proposal, ecological risk assessment over a region should be conducted through appropriate investigation in order to identify, on a qualitative/conceptual basis, the stressors acting on ecosystems in the region of study, the relevant types of ecosystems and habitats that are present, and the likely causal relationships between stressors and impacts on ecosystems. Once these three elements are clarified, they propose to express risks simply in terms of their overlap (Figure 20.1), using an appropriate ranking system. In order to clarify this concept, the authors propose the following example. Let us consider a coastal region where three habitats can be discerned: a river delta, a subtidal ...