Freezing of Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 24

Table 2.6 Lake classification systems
Background Object Basis

Geological Lake basin Origin of the depression where the lake has formed

Physical Size Horizontal extent and depth

Geochemical Salinity In fl uence on water density and other properties

Limnological Mixing Frequency of convective overturn of the water mass

Optical Colour Optically active substances

Biological Trophic status Level of nutrients

Cryospheric Ice Quality of ice season

solutions (the unit is mg Pt, which refers to the concentration of dissolved platinum).
Generally, in clear lake waters the Secchi depth 4 is more than 5 m, while it is less than 1 m in
strongly brown, turbid or eutrophic water. The optical thickness of lake water, de ned as the

e-folding distance of light intensity, provides the scale for the mixing depth in calm waters
due to solar heating.
The biological classi

cation is based on the trophic status. This contains the ultra-
oligotrophic, oligotrophic, mesotrophic, eutrophic, and hyper-eutrophic categories. The
trophic status is related to the concentrations of phosphorus and nitrogen, that is re ected

in the optical quality of the water. Therefore the response of a water body to the ice period
depends on the trophic status. Consumption of oxygen is much faster in eutrophic or
hyper-eutrophic lakes and they reach more easily anoxic conditions in winter.
A summary of the lake classi

fl

cation systems is given in Table 2.6 . There have been
approaches to classify the size of lakes on the basis of physical processes. Example the
background can be the Coriolis acceleration, which leads to the use of the Rossby radius
of deformation as the size criterion (Kirillin et al. 2012). Ashton (1980) classi ed freezing

lakes into small lakes (lakes with stable ice cover), reservoirs (stable ice cover and
signi

cant through fl flow), and large lakes (lakes with drift ice).

2.2 Weather and Climate

2.2.1 General Regional Climate

The local climatology determines to a large degree whether a lake freezes over or not.
However, geothermal, hypersaline, and very deep lakes are able to stay ice-free in cold
winters. The world ' s climate conditions are classi ed according to the K ö ppen Geiger

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4 Secchi depth is the maximum depth where a white disk, diameter 30 cm, is visible from the
surface.