Assemblage grouping of European benthic diatoms as indicators of trophic status of rivers

River benthic diatoms are routinely used to monitor water quality in rivers throughout Europe. Many diatom indices have been developed to monitor a single water quality variable such as phosphorus concentration, or organic pollution, and there is a need to develop diatom monitoring methods for the Water Framework Directive (WFD) which can monitor and quantify a range of environmental variables. The identification of benthic diatom assemblages, or biotypes, is an alternative method that may allow monitoring of ecological status throughout European rivers. Multivariate analysis showed that diatom species composition corresponded most strongly to altitude, temperature, pH and conductivity, while nutrient variables were of secondary importance. To assess the use of biotypes as indicators of eutrophic status benthic diatom samples collected from five European countries were grouped on the basis of their species composition using TWINSPAN. Eight diatom biotypes, some with two subgroups, were identified. Canonical Correspondence Analysis was used to investigate the relationship between these diatom groupings and nutrient concentrations, with and without the effects related to altitude and pH. A number of communities which may act as indicators of eutrophication were identified, though issues arose concerning the identification of these communities and the lack of sample sites from a range of altitudes, pH and conductivities. Finally the use of such diatom based methods to set river quality boundaries and monitor trophic status for the WFD is considered in light of their predictive strength, practicability in application and international differences in river monitoring standards.