Benthic mat biomass, productivity (photosynthesis and respiration) and contributions to lake nutrient cycling in Lake Hoare, Taylor Valley

The importance of benthic microbial mat production in the Lake Hoare, Taylor Valley and how the mats are adapted to survive and grow in deep water (extreme low light but no freezing) was investigated. Quantity and quality of light penetrating the ice and light attenuation properties of the water column were determined. Samples of benthic mat cores were collected for analysis of community structure, pigments, nutrients and carbon content, measurements of the response of photosynthesis and respiration to varying light intensities and determination of areal concentrations of chlorophyll a, phycobilin pigments and ash free dry mass. Samples were collected from a wide range of depths. The attenuation of light through microbial mats was determined for samples from all depths and profiling of the water column for other physical, chemical and biological variables was completed. The location of photosynthetic activity within the mats was deduced using a micro-oxygen electrode. Comparative physiological measurements of the mat from different depths were taken in the very dark Lake Hoare for comparison with Lake Vanda. Three sites were sampled for microbial mat collections from a range of depths for analysis of pigments, biomass, composition and nutrients (C and N) and ash free dry weight. A series of experiments were conducted to determine the contributions of microbial mats to lake nutrient cycling and the rate of photosynthesis and nutrient uptake was assessed. Sediment traps, left in situ for several seasons, were recovered and the contents were analysed for organic and inorganic carbon and nitrogen (including isotopic signatures) and pigments. Sediment cores were also taken for paleoecological analysis and long sediment cores from a range of depths including the bottom of the lake (at 24m) were obtained. Groundwater seepage zones were located and long term deployments of instruments in these seeps, designed to determine their role in solute dynamics, were made.