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O—3 m layer amounts 64.64 million m⁶. i.e. 82.3®/o of all water masses and the de-posit layers 0—6 m. 164.6^f/o.

The heat resources of a 3 m bottom deposit layer have been calculated accor-ding to S. N. Taczałow's formula (1966)

Q = P h t c g,

where

P = ground surface in cm* (it has been assumed that the bottom surface equ-als approximately the water surface),

h = 300 cm,

c = specific heat 0.92 cal/g C,

q = average specific gravity of formations in the analyzed layer ca. 1.5 g/cm*.

It has been assumed that the whole lakę basin is covered by homogenous or-ganogenetic bottom deposits. The greatest heat resources in the bottom deposits have been in August 1971 (1139.93 lOBMcal). and in July 1972 (1195.23 10*Mcal). The minimum values have been in January 1971 and 1972 and amounted respectively 588.70 10« and 597.00 10‘Mcal. The average annual resources in bottom deposits in the analyzed years are similar and amount respectively 869.53 10^g and 885.33 10⁶Mcal.

On fig. 35 monthly changes in heat resources have been presented for a 3 m layer of bottom deposits and for lakę water masses. Special attention may be cal-led to the fact that during the existence of the ice sheet a heat resources growth in the water masses takes place. This is possible thanks to the fact that the bottom deposits deliver to the codled water masses heat energy taken from them during the summer period. The minimum average annual temperaturę of the Gopło Lakę water masses (a polymictic lakę) occuring during the setting up to the ice sheet, is directly connected with the above mentioned phenomenon. The maximum intermonthly increases of heat resource of water masses and bottom deposits take place during the period of April—May. The maximum intermonthly decrease oc-curs directly after the maximum values in July and August and before the ice sheet period.

It may be concluded from this work’s own measurements and from other author’s that each exploration of lakę thermics especially of polymictic (tachimic-tic) should be performed on the thermically active bottom layer. A. I. Tichomirow (1970) regards the water masses and the thermically active layer of bottom deposits as a whole. According to his opinion the starting point for the singling out of thermic seasons in a lakę should be the moment when the sum of water masses heat reserves and of the active bottom deposit layer shows the annual minimum. This occurs at the end of winter and beginning of spring. The bottom deposits are the receptors of heat changes in water masses mainly to the great heat inertia. They are an integral part of the lakę from the point of view of heat processes.

The role of the thermically active of bottom deposits in the heat balance of the lakę depends on its thermic type. A. I. Tichomirow (1970) enumerates three basie lakę types: epithermic, metathermic and hypothermic. The bottom deposits of epithermic lakes have the highest and the hypothermic the lowest temperatures. Within the single thermic groups there will be differences too. An affirmation of the correctness of these conclusions are among others the exploration results of L. F. Forsz (1965, 1968), G. E. Likens and N. W. Johnson (1969). These authors were performing parallel measurements of water and bottom deposits temperatures in several lakes. The bottom deposits of each lakę have a different temperaturę which depend strictly on whole of thermic conditions in the water masses. It should be