XV^th International Symposium on Chironomidae - Minneapolis, August, 11^th-15^th, 2003.

Oral presentation : Using chironomids as indicators in implementing the EU Water Framework Directive. Garcia XF, Brauns M, Pusch M, Walz N.

Abstract

The EU Water Framework Directive (WFD) provides a new legal framework for the sustainable management of European inland and coastal waters. As a first step, the WFD requires that the current ecological status of each aquatic ecosystem be assessed by conducting comparisons of current ecological conditions with reference conditions specific to each type of water body, where the water body types must first be defined based on their hydromorphological characteristics.

In order to set up a typology and assessment scheme for the larger lakes of north-eastern Germany, we sampled 31 lakes located in Brandenburg (EU Ecoregion no. 13: lowland plains). We collected benthic macroinvertebrates from the infra-profundal and littori-profundal zones (1.5 to 6 m depth) with an Ekman-Birge grab sampler.

Using cluster analysis, the 31 lakes were classified into different types based on five hydromorphological parameters unrelated to trophic status; viz. mixis, water residence time and mean depth. Based only on mixis and water residence time, the lakes were classified initially into two groups (a group of 16 lakes connected to a river network and 15 lakes independent of a river network). Adding mean depth allowed a further finer classification into a total of four groups.

Using canonical correspondence analysis, it was demonstrated that faunal assemblages are also dependent on mixis, water residence time and mean depth, leading to the conclusion that faunal assemblages coincide with the four abiotic types mentioned above. However, an overlap between lake type and the level of degradation of the 31 lakes is observed, since lakes closely connected to a river network tend to be more disturbed than the others because of the heavy degree of anthropogenic influence to which most the rivers in Europe have been exposed. This makes the identification of type-specific reference assemblages difficult.

Nevertheless, by comparing the abiotic typology and the biotypology using a co-inertia analysis it was possible to assess the level of degradation of each lake for each of the four types.

In such lake studies, chironomids are of great interest as they constitute 50 % of the species recorded. These chironomid species include type-specific and pollution-sensitive species, but also a large number of pollution-tolerant species adapted to different levels of disturbance. As already suggested by Thienemann, chironomids reflect very clearly the ecological status of a lake. Due to their relatively slow temporal population dynamics, their value as ecological indicators appropriate for lake assessment purposes far exceeds that of the plankton.

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