EFFECTS OF HYPOLIMNETIC WATER AERATION AND IRON-PHOSPHATE PRECIPITATION ON THE TROPHIC LEVEL OF LAKE KRUPUNDER

Lake Krupunder is a small, glacial, stratified lake. Before restoratio n it was classified as eutrophic to polytrophic. Stepwise the lake was restored to a mesotrophic status: 1. In April 1990 a deep water aerat ion plant was installed. Although the entire hypolimnion was sufficien tly supplied with oxygen the trophic level remained high because of su bstochiometric natural iron concentrations. 2. In September 1991 a tec hnical iron-phosphate precipitation was carried out, dispensing 1.8 t of iron-chloride-sulfate ('Ferri floc') into the hypolimnion using the aerator. Until July 1992 the chlorophyll-a concentration decreased by 90%/77% (maximum/mean value).