EFFECTS OF CLIMATE-CHANGE ON THE FRESH-WATERS OF ARCTIC AND SUB-ARCTIC NORTH-AMERICA

Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Cent ral northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass chan ges will play an important role in precipitation changes associated wi th climate warming. The snow season in the region is prolonged resulti ng in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall us ually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models ar e in close agreement for this region and predict temperature increases as large as 4 degrees C in summer and 9 degrees C in winter for a 2 x CO? scenario. Palaeoclimate indicators support the probability that s ubstantial temperature increases have occurred previously during the H olocene. The historical record indicates a temperature increase of >1 degrees C in parts of the region during the last century. GCM predicti ons of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnit ude. Precipitation change is as important as temperature change in det ermining the water balance. The water balance is critical to every asp ect of hydrology and limnology in the far north. Permafrost close to t he surface plays a major role in freshwater systems because it often m aintains lakes and wetlands above an impermeable frost table, which li mits the water storage capabilities of the subsurface. Thawing associa ted with climate change would, particularly in areas of massive ice, s timulate landscape changes, which can affect every aspect of the envir onment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water suppl y of lakes in delta regions and which determines the availability of h abitat for aquatic organisms. Climate warming or river damming and div ersion would probably lead to the complete drying of many delta lakes. Climate warning would also change the characteristics of ponds that p resently freeze to the bottom and result in fundamental changes in the ir limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the c hemical, mineral and nutrient status of lakes and most likely have del eterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive, Extensive wetlands and peatlands are an important component of the global carbo n budget, and warmer and drier conditions would most likely change the m from a sink to a source for atmospheric carbon. There is some eviden ce that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation pattern s; to model the thermal behaviour of wetlands, lakes and rivers; to un derstand better the interrelationships of cold region rivers with thei r basins; to begin studies on the very large lakes in the region; to o btain a firm grasp of the role of northern peatlands in the global car bon cycle; and to link the terrestrial water balance to the thermal an d hydrological regime of the polar sea. Overall there is a strong need for basic research and long-term monitoring. (C) 1997 by John Wiley & Sons, Ltd.