Potential of bio-indication of chironomid communities for assessment of running water quality in Flanders (Belgium)

The distribution of chironomid species in small lowland rivers and brooks in the crenal zone of the Zwalm river basin (Flanders, Belgium) was studied. We examined whether a more refined identification of Chironomidae would result in an added value to the biological assessment of the Zwalm river basin, currently based on the Belgian Biotic Index. At the 18 sampling sites, a total of 31 different taxa of chironomids were identified. Identification was at species, aggregate, group, subgenus or genus level. The diversity of chironomid communities and their indicator role for assessment of particular river types and water quality were examined by means of multivariate analysis. Direct ordination of the identified chironomid taxa resulted into three groups of indicators related to the assessment of the water quality of a brook : (1) indicators of a good water quality, (2) indicators of waters enriched with nutrients and organic matter compounds and (3) taxa that were indifferent to water quality. The more refined identification levels provided useful information on the ecology of these organisms and their role as indicator organisms of specific water quality states. Because of the more labour-intensive procedure, however, chironomid identification at these levels will be more difficult to apply within a rapid bio-assessment protocol of running waters.