Identifying key stressors in Danube, Elbe, Llobregat and Scheldt based on regular monitoring data
de Deckere, Eric; Brack, Werner; Ballaer, Bram; von der Ohe, Peter C.
The complexity of current monitoring programs is reduced with respect to frequency, number of stations, matrices and parameters compared to previous national or regional monitoring programs as outcome of the Common Implementation Strategy of the European Water Framework Directive (WFD). This favours the success of method intercalibration and enables the comparison of results, but reduces the overall ambition and quality of monitoring. In this study, some new assessment tools were tested and applied to existing monitoring data from four river basins, namely Danube, Elbe, Llobregat and Scheldt. The integration of biological and chemical assessment tools enabled to indicate major stressors and potential key pollutants that affect different trophic levels used as ecological quality indicators in the WFD. Both biological and chemical data indicated high organic load as one of the major stressors in the Danube River Basin, but the biotic community is affected also by nutrients and toxic compounds. In the Scheldt River Basin, the major stress factors are organic load and eutrophication. Toxic stress is also important, but it was only assessed at a limited number of sites compared to the other stressors. In the Elbe, nutrient concentrations are much higher and therefore eutrophication is an important stressor. The impact of contaminants in both, Scheldt and Elbe, river basins is clearly reflected by the biotic community, and several key pollutants can be identified that have an impact either on algae, macroinvertebrates or fish. Toxic stress seems to be the dominating stressor in the Llobregat River Basin. The results show the added value of a multiple lines of evidence approach to identify major stressors, which is necessary to develop adequate programs of measures. However, this can only be done on a comprehensive monitoring data set, in which all compartments are included in the monitoring strategy.