Ice-Covered Lakes Environment - Freezing of Lakes and the Evolution of their Ice Cover - page 245

These communities can grow into large stocks and fuel benthic food webs up to higher
trophic levels including

fish and birds.
The temperature of liquid water body is between 0 and 4 C in ice-covered freshwater

lakes. The low temperature is not a strictly limiting factor but it slows down the rate of
metabolism and growth of living organisms. Since salinity depresses the freezing point, in
brackish lakes the minimum temperature of liquid water is

°

C while in saline lakes it
can be much lower. In shallow lakes, which freeze almost throughout, salt rejection from
growing ice depresses the freezing point and the remaining water layer can be highly
saline. If a saline, ice-covered water body is strati

1.3 °

-

ed in salinity, solar radiation can heat
the lower layer into quite high temperatures, as long as the salinity difference can prevent
convection. By this mechanism, deep-water temperature has reached up to 14

° C in the

Canadian High Arctic (Van Hove et al. 2006).
Lake ice as a habitat of biota has been investigated in the recent decades (Laybourn-
Parry et al. 2012), but most of this research has involved perennial lakes in the Antarctica
(e,g., Priscu et al. 1998). In general, inside ice and snow cover, the presence of liquid
water is the limiting factor (Fig. 8.1 ). But as soon as there is liquid water, microbial life
will occur. In the melting season there is always liquid water present inside ice due to
internal melting, and earlier in the ice season flooding brings lake water to the snow-ice

interface. Brackish and saline ice contains brine pockets, which serve as habitats of life.
They have very low temperature and high salinity in cold winter periods. Sea ice biota in
brine pockets has been widely examined in polar and brackish marine basins (e.g., Arrigo
2003; Rintala 2009).

fl

8.1.2 Water Quality

The water balance, circulation and mixing together with the in ow of matter

determine the water quality of lakes. Circulation dynamics result in transport and diffusion
of water with its constituents, and geochemical and biochemical processes modify the lake
water chemistry. The amount and composition of dissolved and particulate matter in the

fl ow and out fl

Fig. 8.1 Liquid humus water
pocket inside a lake ice sheet.
The size of the brown pocket
is 5 mm