Regional and circadian oxygen determinations in Lake Balaton concerning the eutrophication of the lake

Entz, Béla (1976) Regional and circadian oxygen determinations in Lake Balaton concerning the eutrophication of the lake. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 43. pp. 69-82. ISSN 0365-3005

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Abstract

1. The method to determine the productivity of different sections of Lake Balaton by oxygen measurements is suitable due to its simplicity, fastness and valuation in situ by semi-synchronic studies. 2. The thermal stability of Lake Balaton has been studied for the first time. It could be stated that by calm weather due to surface cooling down at night, the thermal stability conditions changed basically in summer-time in the shallow lake, causing vertical mixing of the whole water column. This process is in particular promoting a suitable oxygen supply of the deeper water layers and is in spite of its short duration an important limnological factor. As soon as the thermal stability (S) surpasses by calm weather overday 0.1 mkg/m2, the vertical water movements are blocked and microstratification appears. This stratification can be only dissolved by wave action at a windspeed of 2 to 4 m/sec. 3. The value of thermal stability in the open water was at night occasionally negative ( -0.029 mkg/m2 was measured in July and -0.007 mkg/m2 in August). During daytime by calm weather the stability values increased gradually up to 0.5 mkg/m2 in a water column not deeper than 250 cm. 4. The amount of dissolved oxygen reached in July 10.8-16.0 mg/1 at a temperature of 22.0-25.5 °C. The corresponding values were in August 8 -15.5 mg/1 at 21.5 to 23.8 °C. 5. It is worth mentioning how important life effecting differences (microstratification) can develop within a few hours in shallow (2 to 3 m deep) calm water due to temperature and light conditions in huge water masses. 6. The oxygen saturation values were low in autumn 1975 indicating no alga invasions accompanied by fish kill in the winter half year 1975-76. This hypothesis was assured in time. 7. The rate of oxygen production was decreasing gradually from the Keszthely area till the line between Badacsonytomaj and Fonyód. From thereon even and relatively low values could be noticed up to the NE end of the lake. It could be concluded that there was no further expansion of the highly the highly eutrophic lake section in 1975 as compared with previous years.

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