[Molecular nitrogen fixation in eutrophic Beloye Ozero].

The rate of production and mineralization of organic matter and the rate of fixation of molecular nitrogen were assayed in th eutrophic lake Beloye (near Moscow) at the end of summer stagnation (1976). The content of hydrogen sulphide reached 6.8 mg per litre which resulted in a change of the ecological environment in the lake. The fixation of molecular nitrogen in water layers was characterized by three maxima: 5.0 mcg N per litre per 4 hours (surface); 4.2 mcg N per litre per 4 hours (metalimnion) and 2.8 mcg N per litre per 4 hours (at bottom). The fixation of nitrogen in the trophogenous layer involved mainly the blue-green alga Anabaena. In the sulphide zone, molecular nitrogen was fixed by butyric and sulphate-reducing bacteria.