A Móra Ferenc Múzeum Évkönyve, 1974/75-1. (Szeged, 1975)

Molnár Béla–Szónoky, Miklós: On the Origin and Geohistorical Evolution of the Natron Lakes of the Bugac Region

5 to 7 thousand years ago. Morphologically, the surroundings of the two lakes emerge to higher elevation onyl at great distances. Hence the resutl that, unlike in the case of Lake Kerek, the ground-water table here will sink much below the level of the lake bottom in extremely dry years. In such cases the lake area runs dry. Accordingly, the plants requiring a permanent water body or constant humidity (moisture) can settle in it only temporarily, to die and decay after words. This temporary vegetation, however, is not sufficient for peat formation. Therefore, not peat, but a finegrained sediment with calcareous silt is now being deposited in Lake Bogárzó and Lake Ródliszék. Since the hazelnut phase the wind-blown sand fill of the lakes has decreased the lake area considerably. A common characteristic of the two lakes is their shallow, not more than a few decimetres deep, water body. It is recharged from ground-water and meteoric waters. It is particularly the rechargint effect of the ground-water flow that is significant. The precipitations falling into the lake and the waters flowing in from surface watercourses are of smaller quantity than the annual amount of evaporation (M. Andó 1966, I. Miháltz—

M. Mucsi 1964). The resulting water surplus can onlyderive from ground-waters. Because of the heavy evaporation in summer time, the water of the lakes is alkaline, a phenomenon also due to the shallow depth and relatively large surface of the water body. The water-covered parts of the lakes will consequently change their areal extension. All these circumstances, will largely enhance the alkalization, the development of ,,szik"-soils, in their surroundings. The most heavily alkalized areas always occur in the immediate vicinity of the lakes, where the largest quantity of water evaporates. In these places the downward percolation of meteoric waters is impeded to a great extent by the fact that the sediments of lowest permeability are usually localized here. The alkalization of the vicinity of the lakes is provoked, beside the given hydrogeological characteristics, by the inreasing concentration of the salts of the groundwaters and meteoric waters. The salts are dissolved from the sediments of the surrounding areas. Because of the presence of sediments of high CaC0

3 content, limericher alkaline soils, ,,szik"-soils, have been formed in the Danube

—Tisza Interfluve, so in the regions of the two lakes as well. It can thus be concluded that, despite the many features that are the same in both the Bugac lakes and in the other lakes of similar development of the Danube

— Tisza Interfluve, the former show a number of specific individual features. It is therefore desirable to continue the investigations in order to get acquainted with the individual characteristics of each lake : a knowledge that may allow a better understanding of the general laws and regularities. BIBLIOGRAPHY Andó, M., (1966), Mikroklimaverhältnisse der sodahaltigen Teiche im südlichen Teil der Grossen Tiefebene. — Acta Geographica, Acta Univ. Szegediensis, 6. 1—4, pp. 23—53. Andó, M.

—Mucsi, M., (1967), Klimarhitmen im Donau

—Theiss-Zwischenstromland. — Acta Geographica, Acta Univ. Szegediensis, 7. 1—6. pp. 44—53. Kriván, P., (1953), Die Bildung der Karbonatsedimente im Zwischengebiet von Donau und Theiss. — Acta Geol. Hung. 2. pp. 91—108. Miháltz L, (1953), A Duna—Tisza köze déli részének földtani felvétele. — Magy. Áll. Földt. Intézet Évi Jel. 1950-ről, pp. 113—143. 269