Paucity of Nutrient Cycling and Absence of Food Chains in the Unique Lakes of Southern Victoria Land

Summary

Some of the lakes of southern Victoria Land, representing the highest latitude (77°S) lakes investigated in the southern hemisphere, are older than most glacially carved lakes. Features which combine to make these lakes unique include the 3.50–6.0 m thick, poorly transparent, turbulence-inhibiting perennial ice covers which overlie strongly physically and chemically stratified water columns. Specific non-biological factors influencing the structure and functioning of the relatively simple planktonic and benthic communities of these lakes are: a widely variable but normally limiting photosynthetically available radiation (PAR); stable low temperatures; high salinities (at greater depths of some lakes); supersaturated oxygen (at shallower depths); low turbulence and a virtual lack of vertical mixing; and frequent phosphorus and sometimes carbon dioxide limitations. Although a few unique, endemic algal and bacterial species occur within these lakes, a more striking feature is the low diversity of physiologically adapted strains of quite cosmopolitan taxa comprising the bulk of the planktonic and benthic communities of all the lakes. Also striking is the virtual absence of consumer animals, except for a few protozoa. The dominant plankton consists of a sparse assemblage of continuously swimming eukaryote micro-algal flagellates and non-swimming heterotrophic bacteria. The benthos of much of these lakes is covered with a great biomass of bluegreen algal-diatomaceous mats. The combined limitation of light, low temperatures, and low nutrients maintain the oligotrophic state of these lakes, and inhibit both decomposition with recycling of nutrients and the development of a significant food chain. Losses of nutrients to the accumulating sediments and losses by the algal mats, which escape through the perennial lake-ice and are blown away, combine to perpetuate the conditions of low productivity and low decomposition.