Ecological concern as a factor in the optimal attenuation of diverse stressor sources in a stream

The use of an objective function based on fuzzy ecological effect expectati on in a genetic optimisation algorithm to obtain site or situation specific stressor attenuation values for the management of diverse stressors emanat ing from several sources is investigated. The approach is based on the prem ise that both regulator and regulatee are able to formulate their goals in fuzzy terms. In the case of the regulator the goals will be formulated in t erms of acceptability of levels of ecological concern (a fuzzy analogy to e cological risk). In the case of the regulatee it will be formulated in term s of acceptability of the level of attenuation. which is also the control v ariable. A hypothetical catchment is used to illustrate the principle.