Should rare river types be given special consideration under the WFD?

Abstract:The Water Framework Directive requires all EU Member States to improve, sustainably manage and protect water quality in all surface waterbodies. To achieve this goal the ecological status of all our streams, rivers and lakes must be assessed against type-specific reference conditions. A number of distinctive or rare river types were not adequately represented in the development of the existing national river typology in 2005, and so it is not known whether they are sufficiently characterised by the current 12-type river typology or represent distinct types. ‘Rare’ in this context refers to systems with a naturally variable or unusual combination of environmental conditions (e.g. naturally low pH) rather than a limited distribution. The rare or distinctive river types highlighted were: (1) groundwater-dominated rivers; (2) highly calcareous rivers with calcium precipitation; (3) low conductivity, naturally acidic rivers; and (4) rivers strongly influenced by lakes (lake outlets). Whether or not these river types host distinct biological communities has yet to be established. While there is a large body of research on the macroinvertebrate communities, research on other biological quality elements such as diatoms is limited. This paper summarises the literature available on the biological characteristics of these rare or distinctive river types.