Nitrogen fixation in a mangrove system, Hinchinbrook Island, north Queensland

Nitrogen fixation was studied in the mangrove forests adjacent to Missionary Bay and in a salt flat near Double Creek, Missionary Bay, Hinchinbrook Island in the summer, winter and spring of 1989.The rate of reduction of acetylene during incubation of samples in airtight chambers was used to estimate nitrogen fixation rates. Acetylene and ethylene in the incubation mixtures were analysed simultaneously by gas-liquid chromatography. Acetylene reduction rates were converted to nitrogen fixation rates using the theoretical factor of three acetylene molecules equivalent to one nitrogen molecule.Three or more replicate samples of the following sample types were analysed:- forest sediments from low, mid and high intertidal sites- salt pan sediments- salt pan sediments covered with blue-green algal mats- prop roots with thick growths of mixed species turf algae from low, mid and high intertidal sites- decomposing logs containing varying amounts of teredinid molluscs.Some samples were discarded due to faulty equipment.
This study was initiated to investigate the relative importance of various sources of nitrogen fixation and the seasonal variation in nitrogen fixation in mangrove forests and salt flats. From these data estimates of nitrogen fixation for the whole forest were made.