Development of microbial mats on contaminated soils from the former site of Vanda Station, Antarctica

A series of experiments were undertaken to determine the extent to which contaminants present at the site of New Zealand s now dismantled Vanda Station, Antarctica, affect the microbial commu­ nities likely to develop on such soils. Contaminated soils had higher concentrations of nutrients (N and P), organic material and some metals (Ag, Cu, Cd, Pb) relative to a control site. We found that contaminated soils supported an enhanced rate of growth and final yield of algae compared to control soils. Species composition was switched from primarily cyanobacteria to include a high proportion of green algae. A similar enhancement could be achieved by enriching control soils with N and P. Low level contamination with metals, either in soil from contaminated sites or in enrichments applied to control soils, had no deleterious effect on mat growth or composition. High levels of contamination with metals led to inhibition of growth of both algae and cyanobacteria. The algal mat growths which developed on contaminated sediments prevented nutrient contaminants within sediments from entering the water column when the mats were illuminated. However, in darkness, particularly in the absence of oxygen, nutrients were released from contaminated sediments. The freeze-thaw process also released nutrients from microbial communities. Overall, microbial matforming communities, which are characteristic of Antarctic inland moist habitats, were shown to be sensitive to the types of contamination which were found at Vanda Station. While the growth of mats on contaminated soils could to some extent ameliorate the effects of contaminants by restrict­ ing sediment-water exchange, this effect only occurred during periods favourable to growth and considerable release is likely during periods of anoxia, or in response to freeze-thaw processes.