Geoscience Reference
In-Depth Information
Lake ecosystems need to adapt to changes in lake ice climatology. The connection
between lake ecology and physics is strong in that the ice cover structure and properties
provide information about light level in the water, presence of open water spots, and liquid
water within the ice sheet. Rapid changes bring stresses through light and temperature
conditions as well as through budgets of oxygen and nutrients. Climate change issues also
necessitate a better understanding of the role played by a lake ice cover in the emission of
greenhouse gases, especially methane, into the atmosphere, and in the global carbon
budget.
The impact of these changes on the ecological status of lakes is less clear and is the
topic of future investigations. The key questions are the physical implications of lake ice
fracturing and the in
uence of the projected changes in the ice structure on the transfer of
light. When a lake is frozen, the circulation in the water column is weak and driven by
solar radiation and heat
fl
flux from the lake bottom. These weak circulations are, however,
known to be ecologically important since they in
fl
uence the oxygen budget, regulate the
growth of phytoplankton and have a major effect on the winter survival of lake
fl
sh.
For human living conditions, shorter ice seasons, while extending the open water
season, would severely or even drastically limit the traditional on-ice activities. A key
point is the stable ice period when the thickness of the ice is above the critical level of
about 30 cm. Then the ice is a stable platform for on-ice traf
fishing, and recreation.
Even a modest warming will have a major impact on the ice season viewed from this
practical viewpoint. On the other hand, the lakes would be open for a much longer period
and allow the extension of many water-based activities. For the ice cover to be
c,
,it
has to be thick enough to serve as a solid platform. Lakes in the ephemeral zone, and to a
lesser extent those in the unstable zone, are not useful in that sense. A warming by 2
useful
C
may reduce the ice thickness about 20 cm that would mean below the critical level
throughout southern Finland and corresponding climatic zones. Even then, the length of
the ice season could still be 3 months (see Yang et al. 2012). If there were a continuous
warming climatic trend, these qualitative changes would become obvious toward the end
of the 21st century.
To understand more about the winter conditions in freezing lakes, further research is
ongoing on lake ice physics, ecology and engineering. It is expected that this research will
continue growing in the near future. The main motivation is the impact of environmental
loads and climate changes on the ice conditions. Lake ice seasons are of concern in The
Global Lake Ecological Observatory Network (GLEON), Society of Limnology has
established a Working Group on Winter Limnology, and lake ice sessions are run in the
Ice Symposium series of the Ice Committee of the International Association of Hydro-
Environment Research (IAHR).
3
°
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