Sampling strategies for phytoplankton investigations in a large river (River Danube, Hungary)

The results of phytoplankton studies ont he Hungarian stretch of the Danube are analysed with the focus on questions of a sampling frequency. Phytoplankton samples were taken weekly upstream and downstream of Budapest during a long-term project. Six short-term periods were investigated more intensively, with 4-8 samples/day over a 2-4 day period. The qualitative composition of phytoplankton samples were investigated. It is suggested that the sampling frequency should vary during the year in a large eutrophic river like the Danube. It is important to have up-to-date details of water discharge, too. There is a need to know both the present water discharge and the pattern of probable changes int he near future, using forecasts of the water discharge registration service. In mid-winter the sampling frequency can be monthly. Int he adjacent cool seasons, in February-March and in November, sampling shoud be at a 2-3 week frequency. From April to October the frequency can be biweekly in high water periods (during the floods), but we recommend sampling every 7-10 days under low flow conditions. A special „time average” sampling-method is useful int he low water period

Diatom composition of the rheoplankton in a rhithral river system

Diatom composition of the rheoplankton (phytoplankton) in the Sajó- Hernád river system (Slovakia and Hungary) was studied. Forty two sample sites were designated on the watershed from source to mouth of the two rivers and their tributaries. Samples were taken in July 2012. Altogether, 258 diatom taxa were identified. The microflora was dominated by tychoplanktonic elements. According to the relative abundance of the occurring taxa, four groups could be distinguished. Differentiation of these groups was confirmed by differences in the habitat characteristics, viz. altitude, width of watercourse, macrophyte coverage and river bed material. Diversity of diatom taxa in the phytoplankton was also studied. A positive relationship was found between the macrophyte coverage and the Simpson and the Shannon indices. In contrast, a negative relationship was shown between the macrophyte coverage and Berger-Parker diversity, in which metric the role of the dominant taxa is emphasized. Although the phytoplankton in rhithral rivers is influenced by stochastic events, our results reveal that geographical and hydromorphological characteristics of the rivers and coverage of macrophytes can also play role in shaping the composition and diversity of the phytoplankton