Ecological investigation of nitrogen sources and sinks in Lake Wilson and three catchment ponds in the Darwin Glacier region

Ecological investigations into the waters of the Darwin Glacier region (extreme southern end member to the Dry Valley system) were carried out to extend knowledge of microbial processes to high latitude and an area unique in water chemistry. The study focuses on nitrogen in the area as high nitrate values have been identified in the meltwater of the catchment of Lake Wilson at the lower end of the Darwin Glacier. The vertical stratification of Lake Wilson was examined. The mid-part of the lake was sampled where profiles of upward and downward irradiance was measured for water clarity and water column properties/vertical stratification (temperature, conductivity, pH, major and trace inorganic ions, dissolved gases, chlorophyll a and nitrogen compounds). The biomass, distribution and taxonomic composition of the microbial community were determined from samples. Bacterial activity was assessed by assays of denitrification, nitrification and dark CO2 uptake. Primary production was assessed with the incubation of phytoplankton at different light intensities and measuring photosynthesis. Three series of melt ponds in the catchment were studied with ice cover, thickness, water colour, depth, size, temperature (soil and water), conductivity, pH, nitrate tests, description of the area and algal species present and characteristics of the benthic mats investigated. Several assays were run on the metabolic activity of the mats from different ponds including photosynthesis and respiration rates, nitrification by dark 14C uptake in the presence of nitrapyrin, and nitrogen fixation.