The use of biotopes in assessing the environmental quality of tidal estuaries in Europe

In Europe, the Water Framework Directive (WFD) (European Commission 2000) – and the recently proposed EU Marine Strategy Directive – have established a framework for the protection of groundwater, inland surface waters, estuarine (transitional) waters and coastal waters. TheWFD has several objectives: to prevent water ecosystem deterioration, to protect and to enhance the status of water resources but the most important aspect is to achieve a ‘Good Ecological Status’ (GES) for all waters, by 2015. In essence, the WFD requires a water body to be compared against a reference condition and then its ecological status designated – if the water body does not meet good or high ecological status, i.e. it is in moderate, poor or bad ecological status, then remedial measures have to be taken (e.g. pollution has to be removed). Many indices were developed from benthic work and are often thought fit for purpose. Based on the successional model proposed by Pearson and Rosenberg (1978), most of these indices were effectively established for soft sediment benthos. However, those developed in the framework of the WFD were derived from work on the subtidal. They are difficult to use in the intertidal and in transitional waters. As they were derived from work on organic pollution, there is no or little evident link with chemical and physical pollution. Ecomorphology brings together a biological approach and a sedimentological approach to estuarine ecology. It considers the use of the biotope and related concepts (biocenosis, bio-facies, ecotone, habitat…) as a basis to a novel approach to environmental quality assessment. It addresses the problem of the estuarine quality paradox in recognising the role of nutrients and organic matter in biogeochemical cycles. The discussion shows the complementarity of biotopes with the Sato-Umi and the ecohydrolgy approaches.