title: Comparative test of ecological assessment methods of lowland streams based on long-term monitoring data of macrophytes.
abstract: Ecological assessment of water courses is required by the European Water Framework Directive (WFD). Assessment by means of macrophytes is impeded by insufficient knowledge on the relations between assessment scores and the dynamics of environmental parameters. Data from a long-term observation of macrophyte dynamics over 21 years in two lowland rivers were used for testing the performance of six widely used assessment methods. Six sample sites situated in two lowland streams were selected. Four sites were classified as of moderate habitat quality and two sites as of poor habitat quality in the context of WFD. Assessment methods generally showed a poor performance in recognizing the ecological status of the annual observations. Status was more often over- than underestimated. Performance of methods differed among individual rivers and among river zones. Assessment scores mostly showed a steady decline, even though all sites obviously remained in the same habitat quality class throughout the observation period. Variation of most environmental factors was largely unrelated to assessment scores. Fluctuations of assessment scores were partly related to single natural disturbance events such as high discharge. Increased shading by marginal trees was reflected negatively by most assessment scores. Assessment scores were highly correlated with species richness and total abundance. The best overall performance was shown by the North-Rhine Westphalian (NRW) method. In contrast to single metric methods it can be adapted to individual properties of a reach in a flexible way. Macrophyte assessment based on the pressure-impact framework did not lead to a satisfying result in our case study. Improvement of species assessment scores and inclusion of functional properties such as growth form may help to overcome the present difficulties.
authors.affiliation: General Ecology, Faculty of Environmental Sciences and Process Engineering, Brandenburg University of Technology Cottbus-Senftenberg, Platz der Deutschen Einheit 1, 03046 Cottbus, Germany. Electronic address: Wiegleb@b-tu.de.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wiegleb
authors.affiliation: Department of Ecology and Environmental Protection, Poznan University of Life Sciences, Wojska Polskiego 28, 60-637 Poznan, Poland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gebler
authors.affiliation: lanaplan GbR, Lobbericher Straße 5, 41334 Nettetal, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: van de Weyer
authors.affiliation: Faculty of Biology, Department of Aquatic Ecology, University of Duisburg-Essen, Universitätsstraße 5, 45141 Essen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Birk
mesh_terms: D004463:Ecology; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D010944:Plants; D045483:Rivers / Q000737:chemistry; D014876:Water Pollution / Q000706:statistics & numerical data*
keywords: Biological assessment; Ecological status; Indicator value; Macrophyte indices; Reference states; Time series analysis