Nitrogenase fixation occurred in a number of habitats in and nearby several antarctic lakes. The observed acetylene reduction occurred in bluegreen algal mats in littoral areas that received maximal sunlight. The benthic bluegreen algal communities in reduced light under 5-6 m of permanent ice showed no detectable nitrogenase activity. The observed nitrogen fixation potential correlated with the presence of heterocystous bluegreen algae considered to be the major nitrogen fixing organisms in these habitats. The relatively low acetylene reduction rates suggest that a small but significant contribution of ammonia to these environments deficient in nitrogen may occur through nitrogen fixation. / Master of Science