Ice Across Biomes
Lake and river ice
Greater variability from year to year, as well as overall trends toward shorter duration of lake and river ice, are closely linked to increasing spring and fall air temperatures.41-43 Ice is an important part of aquatic habitat and changes in ice cover alter a range of conditions, including length of the growing season for algae, water temperature, and levels of sediment and dissolved oxygen.44 Ice conditions also affect land animals by controlling access to the shoreline and to routes across lakes and rivers.45
Trends in the timing of spring ice break-up on large lakes
Lake-ice break-up is generally occurring earlier in the spring (1.8 days earlier per decade, on average). Ice freeze-up for the same set of large lakes (over 100 km2) shows a trend to later in the year (1.2 days per decade on average) for the majority of lakes – but less confidence is given to these fall measurements. The northern lakes showed the strongest rate of change, both in spring and in fall. This analysis is based on a combination of ground-based and remote-sensing data. Trends for the six most northerly lakes are based only on remote-sensing data from 1984 to 2004.49
Change in Great Lakes ice cover
Ice cover forms in near-shore areas of the Great Lakes in December and January and in deeper offshore waters in February and March.47 It affects the temperature of the lakes and the timing of spring overturn (the mixing of the top water layer to the bottom).47 This in turn has an impact on the availability of coldwater habitat for coldwater species such as lake trout.48 Less ice cover leads to earlier spring overturn, earlier warming of deep water, and less coldwater habitat.
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