Structure, seasonal dynamics of macrozoobenthos, bioaccumulation of heavy metals and sabrobiology of the Slovak Danube river section

Regarding the international and transboundary character of the Slovak Danube river section, taxonomic and saprobiological investigation of the benthic fauna has been realized regularly. Many species of this community are considered the suitable organisms for saprobity assessment. They dispose of high indicative abilities, which are necessary for water quality assessment. The macrozoobenthos samples were collected quantitatively from January 1997 to July 1998 from gravel or sand-mud substrate of littoral zone. They were sampled by Kubicek bentometer of (30x30x60 cm) for 10 minutes, whereby the quality was completed by circular net 30 cm in diameter, modified by commonly used kocking technique for 5 minutes. In both cases the mesh size - 0.3 mm were used and the samples were taken at 1-3 month intervals. Unfixed samples were separated under a stereomicroscope and quantitative parameters of taxonomic groups - abundance and biomass were determined as well. Questionable taxa were preserved in 70% ethylalcohol and identified later according to the identification keys by Biro (1981), Caraescu et al (1955), Widerholm (1993), Rozkosny (1980), Losos (1996), and others. List of benthic taxa was conscripted as a result. Dominance of individual taxa was calculated on the basis of the five-grade scale, whereby data in Appendix 1 represent the highest degree attained during the investigation. The abundant crustaceans of Gammaridae or big mussels of Unionidae were sampled separately for the purpose of heavy metals bioaccumulation analysis. These organisms were taken by circular net described or collected by hand. According to the results it can be state that the investigated macrozoobenthos community in the Danube river has consisted principally of permanent fauna. It is characterised by a high biomass and long development cycles. This fact has caused the effective efficiency at the water quality assessment from the biological point of view. In the case of saprobity, which fluctuates in beta-scale (except for alpha-saprobic Slovnaft site), the values of diversity indicators have become useful. The diversity is connected with qualitative analysis and on that basis the list of 162 benthic taxa (in total) have been recorded. The examinated taxa have been classified in to 18 systematic groups. Some of found species are considered taxonomically interesting or rare. The Potamopyrgus antipodarum, Pontogammarus obesus, Emphera lineata or Theodoxus transversalis, Ephoron virgo, Leuctra fusca, L. hippopus respectively can be mentioned as example. The quantitative data required for diversity index calculation were determined as abundance of taxa. Consequently the abundance and biomass of selected groups were determined. The most abundant group of permanent fauna - Gammaridae and Unionidae with the highest biomass were considered suitable for heavy metal bioaccumulation assessment. In comparison with other matrix, the obtained values corresponded mutually. The increased content of heavy metals in left-side locality Karlova Ves has been connected with pollution caused by left-side tributary the Morava river. Regarding the heavy metals content especially in benthic organisms, the results can be considered as preliminaryt fro the present. Therefore further investigation will be continued. On the basis of result the whole longitudinal profile of Slovak stretch will be evaluated from this point of view