Nándor Oertel

Spatial pattern of water bugs (Nepomorpha, Gerromorpha) at different scales in the Szigetköz (Hungary)

In 2003, 26 Heteroptera species (16 aquatic and 10 semiaquatic) were collected from 53 sampling sites in the Szigetköz region in Hungary. Hyocoris cimicoides and Gerris argentatus were the most frequent aquatic and semiaquatic species, respectively. Large differences both in the species number and species composition were observed among the different flood-prevention areas, arm systems and habitats. Strong negative correlation was found between the average number of aquatic species and current velocity, and a strong positive correlation between the average number of aquatic and semiaquatic species and macrophyte density. From a faunistic point of view, the marsh at Arak is the most interesting and valuable site.

Spatial and temporal variation in biomass and size structure of Corbicula fluminea in Danube River catchment, Hungary

The aim of this study was to reveal the spatial and temporal variation in biomass, density, and size structure of the invasive clam, Corbicula fluminea in the Danube River catchment and to explore the environmental factors determining these patterns. Samples were taken seasonally during the years 2007 and 2008 at 15 sites located along a river continuum from a second order stream to the Danube River. C. fluminea was the most abundant species in the main arm of the Danube; however, it was found in great density in the side arms, too. In the Ipoly River it only occured close to the conjuction, and it was not present at all in the second and third order streams. Regression models were developed to predict dry mass (DW, g) from linear body dimension [shell length (L), mm]. For the description of length-dry mass relationship, the power function (DW = a * Lb) was applied. The highest density, biomass, and mean shell length were 178 ind. m−2, 24.9697 g DW m−2, and 21.99 mm, respectively. ANOVA detected significant spatial variation in biomass; however, significant temporal variation was not recorded between the years, only among the seasons. Multiple linear regressions were used to find the relationship between the biomass and the environmental parameters. The coarse and very fine sediment fractions and the high water temperature provided suitable habitat for C. fluminea. Although statistically significant correlation was not detected between the chlorophyll-a content of water and the biomass, the highest biomass values were recorded at sites with high chlorophyll-a value.

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

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.