12. Arctic Wetlands and Lakes-Dynamics and Linkages

Arctic wetlands can occur as isolated patches with areas of 1–10 km², or they can cover extensive areas in the landscape. Wetlands exert a strong influence on the hydrological cycle as they can both store and release water to streams, other wetlands (ponds) and replenish groundwater reserves. Arctic landscapes are also rich with lakes and their occurrence depends on geology, geomorphic or anthropogenic setting. Like ponds, lake sustainability over time depends on inputs exceeding losses. Hence, their capacity to hold water and the nature of shifting storage capacity especially in light of climate warming (shifts in precipitation/evaporation), or stream/river connectivity, together with growing expansion of mining, oil development are critical issues for northern ecosystems and communities. To survive over time, a wetland or lake needs positive water storage to maintain a high degree of saturation (wetland) or storage capacity (lake). Snow is particularly important, and for Arctic wetlands and lakes, it is the total winter snow accumulation that is of major hydrological consequence. Summer rainfall in most permafrost areas is not high, and often is insufficient to match evaporation rates in lakes. However, the frequency and duration of rainfall can be important for arctic wetlands. Climate warming has been tied to an increase in ground thaw, resulting in both the loss of lakes/ponds and expansion of ponds/lakes depending on permafrost conditions. The timing of ice cover on lakes can affect evaporation, where shallower lakes that experience bed-fast ice during the winter become ice-free sooner in the warm season, which leads to longer open-water seasons and greater amounts of evaporation. Northern lakes have shown shifts towards shorter ice cover duration during the cold seasons, resulting in longer open-water seasons. Lake ice modelling suggests continued shifts towards earlier break-up and later freeze-up may be expected.