RECOMMENDATIONS FOR THE ROUTINE SAMPLING OF DIATOMS FOR WATER-QUALITYASSESSMENTS IN EUROPE

Many methods for using diatoms for routine monitoring of water quality have been developed in Europe and in some countries, these are being used to enforce environmental legislation. In order to facilitate thei r wider use, particularly with respect to European Union legislation, steps are being taken to harmonize methodology. In this paper, the pri nciples and practice of sampling are described in relation to the main habitat types encountered in Europe. Although details of methods and sampling programmes have to be tailored to particular circumstances an d the overall objectives of the monitoring, a number of generalization s can be made. Where available, rocks and other hard surfaces are the preferred substrates and methods for sampling these are described. If such substrata are not available, then introduced ('artificial') subst rata have many applications. Various types of introduced substrata can be used successfully, so long as some basic precautions are described . Other types of substrata such as macrophytes and macroalgae may also be useful under certain circumstances, although there is less consens us in the literature on the most appropriate methods, and of the valid ity of comparisons between indices computed from epiphytic and epilith ic communities. When designing surveys, it is recommended that as far as possible, extremes of non-water quality factors (e.g. shade, curren t speed, etc) are avoided, unless these are characteristic of the syst em under investigation. Detailed guidelines for sampling epilithon are described. Along with the recommendations for sampling other substrat a, it is hoped that these provide a framework that can be adapted to m ost river types in Europe.