Modeling the chemical and toxic water status of the Scheldt basin (Belgium), using aquatic invertebrate assemblages and an advanced modeling method.

Self-Organizing Maps have been used on monitoring sites in several Scheldt sub-basins to identify the main aquatic invertebrate assemblages and relate them to the physico-chemical and toxic water status. 12 physico-chemical variables and 2 estimates of toxic risk were available for a dataset made up of a total of 489 records. Two of the five defining clusters reflecting a relatively clean environment were composed by very well diversified functional feeding groups and sensitive taxa. The cleanest assemblage was mainly linked to the sites from the Nete sub-basin. The three other clusters were inversely described with a dominance of oligochaetes and deposit feeders as well as a bad water quality. Such an analysis can be used to support ecological status assessment of rivers and thus might be useful for decision-makers in the evaluation of chemical and toxic water status, as required by the EU Water Framework Directive.