Assessment of ecological effects and risks

The aim of this presentation is to give an outline of a system for ecosystem indices, based on a holistic ecosystem perspective. One purpose of ecosystem indices is to give politicians and the public a more easily understandable account of the environmental status and how it changes in relation to defined threats. The approach uses several concepts, like target organisms, target ecosystems, effect variables, environmental sensitivity, and environmental cost/benefit analyses related to remedial measures. Some of the ideas brought forward may be unrealistic because of the complexities involved in establishing simple, practical and meaningful ecological indices. Effect-load-sensitivity (ELS) models for entire ecosystems, like lakes and coastal areas, play a paramount role in this context. The aim of such models is to provide quantitative predictions relating to operationally defined ecological effect variables to compatible load and sensitivity variables. Empirically validated ELS-models provide a tool to simulate ecosystem effects related to practically feasible remedial measures. Practically useful models must be driven by simple, readily available parameters, like 'map parameters' describing the catchment area and the lake. The ecosystem index or the effect variable in ELS-models characterise the entire lake, and not specific sites in the lake, over longer periods of time, and not the specific sampling events. Mean ecosystem indices can be obtained for a region or a country and the development can be illustrated with trend analyses. If these trends are linked to remedial measures, the effects of the remedies can be discussed quantitatively and qualitatively in terms of cost-benefit