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THE THEHMICS BOTTOM DEPOSITS IN LAKĘ EXPLORATION

Summary

The explorations of bottom deposits were madę at the Gopło Lakę and at several smaller lakes of the Wielkopolska — Kujawy Lakę District. The main exploration object was the Gopło Lakę (fig. 5), surface 2154,5 ha, volume 78,5 mil-lions m¹, maximum depth 16,6 m, average depth 3,6 m, depth of geometrical centre of gravity 2,4 m. These data are real with the water-gauge in Kruszwica indicating the water level of H — 236 cm. Basing on 3 yers of observation data it was sta-ted that the Gopło water masses up to depth of 10 m are void of a stable ther-mic stratification. The depth layer 0—10 m contains ca 98°/© of the lakę water volume. Occasional thermic stratification in Gopło Lakę is transitory and shows the tachy-mixic of water circulation, according to P. Olszewskie term (1959), or a polymixy, according to J. Wiszniewskie (1953). Calling the Lakę polymictic should be under-stood that this type of mixy is prevailing.

This is the briefly described character of water masses which are covering the bottom deposits with maximum depth of 16,25 m. According to M. Stangen-berge typology (1938), the surface layer consists of mixed and siliceous deposit groups.

Before starting with regular temperaturę observations of the bottom deposits a series of measurements in different lakę points has been taken. One profile has been chosen (fig. 5) whose data picture approximate average conditions. The water depth in the chosen point is 5 m. The isobath of this value encompasses 70.9°/© of lakę surface and ca 80°/© of the whole lakę volume has the depth of 0—5 m.

A specially constructed probe on the basis of a thermistor thermometer ‘Lis 2’ (fig. 4), has been used for the measurements of the vertical temperaturę distribu-tion. Thermic probing has been madę in monthly intervals. At the same time water temperaturę measurements have been madę in several dozen pointes of the lakę. In each of these points temperaturę measurements of bottom deposits have been madę on the depth of 20 cm. The results of these measurements are compatible with those performed by N. J. Siemionowicz (1954). He had recorded the interdipendence of the temperaturę curve of ground deposits at the depth of several cm and the measurement section shape. In the case of the Gopło Lakę the deposit temperaturę at the depth of 20 cm, the measurement section shape and the water in the measurement point has been taken into account. The shape of the gotten lines suggests the direction of heat interchange between the bottom and the water masses. The interdipendence is not in all eleven explored sections egually distinct. It seema before all to be the result of different exposition of each of the water surfaces of the lakę to factors decisive of the mixing intensity of the water masses. The ex-ploration results have been presented in a schematic diagram (fig. 27). Linę A shows a typical situation for the heat loss period of the water masses, and the