Limnological data of an isolated Dutch broad

Summary Water quality research was started in the province of Friesland, The Netherlands, in order to set the ecological water quality standards. One of the waters under study is the broad of the Boornbergumer Petten. This water, as well as the supplying ditch, was investigated with regard to physico-chemical factors, macro-invertebrates and macrophyte vegetation. Supplementary the broad was sampled on phytoplankton. Preliminary results as well as older limnological data are presented. Macrophytes are the dominating primary producers. Worth mentioning is the extensive vegetation ofScirpus lacustris ssp.lacustris f.fluitans and of someChara species. The Boornbergumer Petten can be regarded as a usable and appropriate reference water for peatdiggings and broads. By means of limnological data of also other waters regional water quality standards will be postulated in the near future. Prepurification of the inflowing water by a marsh vegetation is considered necessary to prevent eutrophication of the broad and may act as a precursor of the appearance of theChara vegetation. Ceasing the inflow of polderwater would lead to drying up of the broad, because of deep draining the surrounding grassland areas.