USE OF ALGAE AND OTHER PLANTS FOR MONITORING RIVERS

A brief account is given of the methods developed for use of algae, bryophytes and angiosperms to monitor rivers and streams. The methods fall broadly into those based on features of populations of representative species, those based on part or all of the whole photosynthetic community and those based on various types of bioassay and ecotoxicological test. The methodology for using bioaccumulation of heavy metals, insecticides and other organic molecules is well developed and has been applied widely in western Europe for practical purposes. Coarse filamentous algae and bryophytes are especially useful, but some angiosperms are suitable, provided general information about bioaccumulation in the particular species is available; it is difficult to use periphyton. Other methods based on species include measurement of genetic tolerance, physiological approaches (chlorophyll: phaeophytin ratio, tissue N:P ratio and surface phosphatase assays) and observations on cyanobacterial and eukaryotic algal morphology. Among community-based methods for monitoring, measurement of biomass is used widely for phytoplankton, but seems of little use for benthos. The use of indices based on benthic communities, especially diatoms, has, however, been applied widely. The earlier indices based on diversity have been replaced almost entirely by ones integrating ecological information from component species. In addition, the authors have started to produce a diatom-based parallel to the macroinvertebrate-based RIVPACS by obtaining floristic data from 'clean' sites. Bioassays and ecological tests, mainly using algae or Lemna, are often carried out together with the other methods.