Decomposition Processes in Maritime Antarctic Lakes

Abstract

The freshwater lakes on Signy Island have been the focus of an intensive research programme for almost 12 years. In this time, considerable information has been accumulated on planktonic and benthic decomposition. This paper brings together the above data and indicates the effectiveness with which organic material is decomposed by micro-flora in both oligotrophic and eutrophic systems. The majority of mineralization in both lake types is aerobic and concerned with readily assimilable organic material. Degradation of phytoplankton debris is slow and mainly occurs in surface sediments. Proteins, lipids, starchy materials, pectin and cellulose are degraded in the top 20 mm of sediment by aerobic and anaerobic heterotrophs. Although sulphate reducers may be present in substantial numbers, data from seasonal sulphate measurements and laboratory experiments indicate that organic sulphur decomposers are probably more significant in Antarctic lake sediments. Recently, methanogenic bacteria have been found in both oligotrophic and eutrophic lakes on Signy Island. High levels of methane build-up under winter ice cover, indicating significant activity even at such consistently low temperatures. From such information it is possible to assess the significance of decomposition by bacteria within Antarctic lakes of different nutrient status.