Composition and dynamics of benthic organic matter in the middle Danube section

Abstract

The organic matter of the sediment is prerequisite for the detritivorous community in the river ecosystem. To quantify this organic matter content and its changes in time and space, investigations were performed at two typical sites of the Hungarian Danube, which differ in their local hydrological characteristics due to the deposition and erosion processes. The distribution of the benthic particulate matter and the organic matter content of that were analysed in the core samples of the river side and the near shore line in three layers (0-5, 5-10 and 10-15 cm) and in four fractions: C = coarse (2360-710 μm), F = fine (710-250 μm), V = very fine (250-63 μm), and U = ultra fine (<63 μm). The variability of the organic matter content was highest in the coarse fraction (CV: 86 %), while it was the lowest in the ultra fine fraction (CV: 20 %). Sites differed mainly in the organic matter content of the C and F fractions, and the vertical changes of the benthic organic matter. The first TBOM records from the studied section of the Danube show relatively high values in comparison with the literature. Results show that mainly the quantity of the fractions (i.e. hydrological characteristics) determined the BOM content of the bed sediments at the investigated sites.