EVALUATION OF BIOLOGICAL RESPONSES TO ORGANIC POLLUTION WITHIN REBECCA DATASET

1.The topic of the analysis of the response of invertebrate based metrics to water pollution has been widely studied in Europe. The argument is at the basis for the implementation of the Water Framework Directive. 2.In the approaches to analyze biota response to pressures, the concentrations of variables indicating organic pollution can be evaluated singularly. In general, the analysis of single parameters furnishes weak relationship with biological metrics because the effect of organic pollution on invertebrate communities is expressed by the simultaneous acting of different parameters. To find strongest relationship, multivariate analyses can be run. The weakness of these analyses lies in the difficulties linked to their interpretation. The strategy can thus be addressed at deriving a simple way to combine chemical parameters in order to get a descriptor which synthesizes the action of these different chemical parameters. 3.Main aim of this paper is to describe the development of this simple indicator for organic pollution suitable to be calculated on different datasets available in Europe. The different chemical parameters are combined assigning them a score. The score, that ranges from 0 and 1, is referred to boundaries obtained as multiples of the 75th percentile of values found in the reference sites. Decreasing scores are assigned in relation to increasing pollutants concentration and different ways of defining classes boundaries are tested. Scores derived from all the available parameters are averaged in order to obtain this simple indicator. Moreover, a option of averaging all the chemical concentration was considered. 4.Data used in this paper originated from existing monitoring datasets for 3 European countries (Sweden, Denmark and Italy) and from a selected Italian dataset collected within the AQEM project. 5.The overall suitability of this descriptor in describing invertebrate metrics variation was evaluated calculating Pearson regression coefficients between the different ways in which the indicator is obtained and biological metrics presently used for the intercalibration exercise run trough Europe. 6.Results showed that the combination of the chemical parameters gives higher Pearson coefficients than if the single chemical variables are considered separately. 7.The main conclusion is that this abiotic descriptor can help in quantify the organic pressure in a meaningful way with respect to invertebrate communities, being able of condensing the information from different chemical variables. The second important conclusion is that, on the basis of the approach used to define class boundaries, i.e. using Reference sites of the same river type as comparison criterion, the performance of this organic descriptor is strictly connected with the correct definition of Reference sites and river types.