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vol-20AZOLLA FILICULOIDES. A NEW EFFECTIVE DINITROGEN
FIXER LAKE EDKU, EGYPT.
By
M. A. EL-SHENAWY
National Institute of Oceanography and Fisheries, Alexandria, Egypt.
Key Words: Azolla filiculoides, Nitrogen fixation, (nitrogenase activity).
ABSTRACT
Azalia filiculoides was found for the first time in Lake Edku in Autumn
1991. A massive population developed in 1992 to cover more than half of
Lake area. In situ nitrogen fixation (C2H2-C2H4 reduction) by Azalia
filiculoides in Lake Edku was measured during the year 1992. The highest
activity was recorded in Summer (73.1 ug-NJ plantl hi), and the lowest
activity was in Winter (10.6 ug-N2 plant·1 h·I
). Ihe contribution ojAzolla to
the nitrogen budget ofLake Edku was computed to be 0.7 kg m·2 y,.-I or 89562
tonnes of nitrogen were fixed annually in the whole lake. This amount
represents about 1.36 times of the annual total combined nitrogen (56700
tonnes) entering the lake via draim, which must therefore be considered quite
significant and should he taken into consideration for the lake management.
