Stratification analysis of the Óhalász Ox-bow of the River Tisza (Kisköre Reservoir, Hungary)

Abstract

Vertical samplings of the Ohalasz Ox-bow of the River Tisza situated within the Kiskore Reservoir were carried out on 6 occasions during 2000-2002 from different depths of the open water above the deepest point of the riverbed. The possible formation of a discontinuity layer was studied. Beside the measurements of physical and chemical water parameters the quantitative estimation of the microorganisms taking part in the transformation of inorganic and organic materials was performed. Although the greatest depth of the former river course is just 5 m, a summer stratification was typical as was proved by in-situ measurements and laboratory analyses: an anaerobic water body was formed under 2-2.5 m depth. The discontinuity layer was clearly proved by an intensive peak in the chlorophyll level, the sulphate-sulphide chemocline, an abrupt dropping of the water-temperature, etc. Interesting was also the dominance of phototrophs again in the deeper anoxic water masses, near the bottom.