In situ primary production,biomass and light regime in the Wolderwijd,the most stable Oscillatoria agardhii lake in The Netherlands

During the entire period of research from 1971 to 1982 Oscillatoria agardhii Gomont was overwhelmingly present in the Wolderwijd. Six years of measurements of primary production has pointed out that the gross production per day firstly is related to temperature and secondly to irradiation. However, the production per year is neither related to temperature nor to irradiation. In a cold summer gross production is as high as in a warm summer due to higher production in the lower part of the euphotic zone.In the discussion attention is focused on production characteristics and light climate in relation to the morphometry of the lake. Up to an average depth of 2.5 m blooming of O. agardhii occurs easily, whilst light saturated production achieves its maximum between 2.0 and 2.5 m depth. Increasing depth leads to photo-inhibition in the upper layers followed by lowering of light saturated production. Only special circumstances such as days with microstratification allow growth, resulting then in a monoculture of the alga.