Estimation of the Readily Oxidizable Organic Matter Reserve and its Effect on the Intensity of Organic Matter Destruction by Bacteria in the Danube River

Abstract

During an international expedition devoted to studying the River Danube in March 1988, the influence of readily oxidizable organic matter on the destruction of organic matter by bacteria was investigated. Readily oxidizable (labile) organic matter (LOM), LOM turnover rate, and concentration of particulate organic matter (POM) were quantitatively analysed. It was found that the minimum values of the parameters studied occurred in the Middle Danube, i.e., the Bulgarian and Yugoslavian stretches of the river. Self-purification did not exceed 23 days. Regarding the Upper Danube (i.e., Austria, Czechoslovakia, and Hungary), higher LOM and POM concentrations, bacterial respiration intensity, and self-purification rates (15 days) were observed. However, the maximum values were found in the Kilia delta (USSR). This was attributed to the great amount of organic matter (OM) in particulates contributed from the upper reaches of the river. At the same time, the Soviet stretch of the Danube was characterized by the most intense processes of destruction of OM associated with aggregated bacterioplankton, which gave higher self-purification rates (up to 9 days).