Nitrogenase activity and estimates of nitrogen fixation by freshwater benthic blue‐green algae

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Abstract
The sandy substrate of Lake Taharoa (west coast, North Island, New Zealand-35.degree.50''S, 173.degree.41''E) is covered by communities of filamentous algae that extend from the exposed beach down to 21 m depth. The algae bind the sand to form crusts and mats which may break off as discrete plates. The dominant species are the blue-greens Microcoleus, Nostoc, Phormidium, Lyngbya, Oscillatoria, Scytonema, Stigonema, Schizothrix, Calothrix, Dictyothrix, Tolypothrix, and Anabaena, with occasional high concentrations of the desmid Cylindrocystis. Nitrogenase activity, measured by acetylene reduction, showed a wide range of rates (4-150 .mu.mol C2H4/m2 per h). Estimates of annual rates of nitrogen fixation by the Taharoa communities are comparable with those for periphytic blue-green algae-dominated systems reported elsewhere.