THE conceptual basis of ecological-status assessments using diatoms

TLDR: In this article, the suitability of existing diatom-based metrics for assessing ecological status, as required by the Water Framework Directive (WFD), rather than developing new methods is assessed.

Abstract: Most member states of the EU have chosen to use existing diatom-based metrics for assessment of ecological status, as required by the Water Framework Directive (WFD), rather than develop new methods. In this paper we assess the suitability of such methods in light of the requirements of the normative definitions of ecological status. In particular, we focus on the rationale for the placement of ecological-status boundaries. As the WFD defines ecological status in terms of the 'structure and functioning' of aquatic ecosystems, we interpret changes in the diatom assemblage in light of changes in entire phytobenthos. Whilst we believe that analysis of diatom assemblages is a sensible approach to developing a first generation of WFD-compatible tools, bearing in mind tight deadlines and limited budgets, the potential of non-diatoms should not be ignored when developing future methods.