From the early explorers onwards, visitors to the Arctic and to Antarctica have commented with great interest on the presence of lakes, wetlands, and fl owing waters. These environments encompass a spectacular range of conditions for aquatic life, from dilute surface melt ponds, to deep, highly stratifi ed, hypersaline lakes. Many of these high-latitude ecosystems are now proving to be attractive models to explore fundamental themes in limnology; for example, landscape–lake interactions, the adaptation of plants, animals, and microbes to environmental extremes, and climate effects on ecosystem structure and functioning. Some of these waters also have direct global implications; for example, permafrost thaw lakes as sources of greenhouse gases, subglacial aquatic environments as a planetary storehouse.
