A method for quantifying conservation value in lentic freshwater habitats using desmids as indicator organisms

A method is presented for quantification of aquatic nature conservation value based on desmid assemblages present. Species richness (indicative of internal structural and functional differentiation of the ecosystem), the occurrence of rare taxa (often indicative of particular environmental conditions) and the presence of species indicative of ecosystem maturity are the parameters chosen to determine conservation value. For the sake of utility, schemes have been developed to transform the values scored for the various parameters to a simple scale ranging From 0 to 10, relative to regional and historical standards. By way of illustration, two examples are presented. The first shows the decline of desmid-related conservation value along a gradient of increasing eutrophication in a series of interconnected shallow lakes, the other illustrates the course of this value through time in a polluted and subsequently restored moorland pool.