The physical and geochemical parameters controlling algal production in Lake Vanda

The factors controlling algal production in Lake Vanda were investigated experimentally by nutrient bioassays and in situ radiotracer incubations. Photosynthetic profiles were measured through the water column. Three displacement experiments (incubation of a single algal community at several depths) were completed to distinguish the relative importance of light and temperature on primary production. Associated physico-chemical variables (nutrients, downwelling irradiance (4 wavebands), temperature, salinity, dissolved inorganic carbon) was measured down the water column at the deepest site. In vivo chlorophyll a fluroescence measurements were made at several locations on the lake. The microbial transformation of nitrogen throughout the water column was measured by taking bacteria profiles (epifluorescence counts and in situ DNA synthesis), measuring nitrification and denitrification rates by in situ assays and sampling nitrous oxide (an intermediate in both processes) at close intervals down the lakes water column. A preliminary investigation of plankton nutrient status in lakes and ponds on Ross Island was conducted with similar methods.