Ice-Covered Lakes Environment - Freezing of Lakes and the Evolution of their Ice Cover - page 243

sets limitations to ecosystems: light is absent or weak in mid-winter, oxygen is not
renewed, and the water temperature is low. Also the renewal of the lake water mass and
nutrients is reduced due to reduced in ows from the cold, frozen surroundings. For the

society, frozen lakes are safety and traf

fl

c issues, and speci c methods are needed for

utilization of lakes and for near-shore construction efforts.

8.1 Winter Ecology

8.1.1 General

The biology of freezing lakes is much less known from field investigations for the ice

season than for the summer. Most of the ice studies are concerned with polar lakes, while
for boreal lakes there are just a few scattered publications (see Salonen et al. 2009).
Primary production is weak in winter in boreal lakes, but as a whole the ecological
conditions in spring and fall are linked through the winter rather than being independent,
and therefore understanding the progress of the winter season is important.
Lake ecosystems cover phytoplankton, macrophytes, zooplankton,

fish and amphibi-
ans. In a very few lakes there are seals, e.g. in Lake Saimaa and Lake Ladoga in Finland
and Lake Baikal in Russia. 1 Freezing lakes provide speci c aquatic habitats, and com-

pared with lower latitudes, the food-web structure is simpli ed (e.g., Vincent et al. 2008).

Arctic and Antarctic lake regions are dissimilar. In the Arctic they are found in northern
extensions of continental land masses, while Antarctica is an isolated continent where
lakes are proglacial. This is reflected in the colonization and biodiversity. Arctic lakes
have more diverse compositions of biota, and in Antarctic lakes

fish are absent and in
many cases even zooplankton is missing. Microbial mats dominated by cyanobacteria are
common in both polar regions but higher plants are not found in Antarctic lakes.
In cold regions, freezing brings limitations to biological activity. Primary production
needs liquid water, carbon dioxide, photons and nutrients. The photosynthesis formula
reads

6H 2 O þ 6CO 2 þ photons ! C 6 H 12 O 6 þ 6O 2 ð 8 : 1 Þ

The wavelength band of light used for photosynthesis is from 400 to 700 nm, called as
the photosynthetically active radiation (PAR) band. It is nearly the same as the band of
electromagnetic radiation visible to human eye. By photosynthesis, plants, algae and
cyanobacteria use the energy of photons to transform water and carbon dioxide into sugar
and oxygen.
Liquid water is available in lake environments, at least for a part of the year, by the

de nition of a lake. But in very shallow lakes and supraglacial lakes the whole water body

1 Lake Saimaa and Ladoga seals are relicts from the time the lakes were connected to the ocean
about 10,000 years ago, later isolated due to land uplift.