Vorschlag zur Bewertung ausgewählter Fließgewässertypen anhand des Phytoplanktons
This study aimed at the development of an multi-metric assessment system for rivers using phytoplankton with respect to the EU Water Framework Directive (EU WFD). The study was restricted to the planktonrich German river types. In a first step the commensurability of river types referring to their potential to build up phytoplankton biomass was analysed. Therefore a correlation analysis of seasonal Chlorophyll a mean values and total phosphorous (TP) concentrations was run with a large data set. Since the observed biomasses for a given TP concentration differed among but clustered within the predefined river types, new sub-types were defined, which were partly described by the catchment-specific run-off value of 10 l s-1 km-2 (lowland and mountain streams) or simply by the catchment size (medium-sized lowland rivers). As TP is regarded to be the most important triggering factor for eutrophication, class boundaries were redrawn in compliance with the EU WFD by extrapolation from the river type-specific geogenic background concentration. The TP class boundaries aided the reconstruction of chlorophyll a reference concentration. Both TP and chlorophyll a were used to define the trophic spectrum of each river type. The final multimetric assessment system uses several metrics, such as algal biomass, algal classes, and indicator taxa. The system is also capable of assessing the impact of anthropogenic salinity, which is reflected by the “Phytoplankton-Halobienindex”.
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