Limnological studies on the eutrophication of Lake Wolderwijd A shallow hypertrophicOscillatoria dominated lake in the Netherlands

Lake Wolderwijd—area 2700 ha, mean depth 1.60 m, residence time 0.9 year—a man-made lake from 1967, was soon dominated by the blue-green algaOscillatoria agardhii, which formed a persistant bloom. Only in spring relatively small proportions of other blue-green algae species occurred. The environment in the lake is continuously controlled and governed by the alga, resulting for instance in a perfect homogeneity in the whole lake with respect to the biomass. The biomass in summer (30–40 mgl^?1 dry weight) is only 30–50% greater than in winter. In winter 10 up to 30% of the time is spend by the alga below 1% subsurface light intensity and in summer 20 up to 60%. The specific oligophote capacities ofOscillatoria agardhii combined with external factors as available nutrients, depth and residence time of Lake Wolderwijd, provide in a high degree of habitat control. Cause and effect of the observed phenomena are integrated in each other. The explanation of the ecological niche of the alga is therefore difficult. Comparison of Lake Wolderwijd with other, less extreme.Oscillatoria lakes in the Netherlands and the research, done by others on continue cultures, are helpful means to approach the ecological niche of the alga. The possibility to create its own optimal light climate at each temperature and incident radiation, among others due to the nonconsumption by zooplankton, is a key factor for the persistant bloom ofOscillatoria agardhii in Lake Wolderwijd. A mean depth between 0.7 and 2.5 m is considered as a conditio sine qua non for this persistant bloom.