Investigations into the Deep Chlorophyll Maximum Layer of Lake Vanda, Wright Valley: How is the DCM established and maintained?

The waters of Lake Vanda, Wright Valley, have risen at a rate of 1m per year. Within the lake there is a biologically important layer, the deep chlorophyll maximum (DCM), where high algal production occurs at 63m depth. The study aimed to understand how this layer has been maintained at this depth in spite of the rise in lake level. Mathematical modelling of the processes which maintain the DCM will allow the extrapolation of the findings to DCMs in other polar and non-polar areas. Water sampling over the deep spot of the lake allowed profiles of temperature, conductivity, dissolved oxygen, dissolved inorganic carbon nutrients, chlorophyll a, suspended solids and particulate and dissolved nutrients to be measured. Penetration of light through the ice and water was determined. Water samples were collected at approx 10m intervals through the water column, and after 60 m, at 2-3 m intervals, and preserved for enumeration of bacteria, picophytoplankton, flagellates, phytoplankton and microzooplankton. Photosynthetic rates of phytoplankton, the relationship between light and photosynthesis and the sinking rate of cells was determined. The toxicity of the water below the DCM was measured. Profiles of sulphate and sulphide concentrations through the water column and sulphate reduction rates in the anoxic zone water and surficial sediment were investigated. The grazing impact of micro-zooplankton on bacteria and phytoplankton was determined and the potential toxic effects of bottom waters on zooplankton were investigated.