András Abonyi

Phytoplankton functional groups as indicators of human impacts along the River Loire (France)

The phytoplankton functional group concept is successfully used to assess ecological status in lakes (Q index), and also provides a method for lotic ecosystems (Q(r) index). Here, we examine the Q(r) composition metric to demonstrate local to regional scale human effects on natural distribution of phytoplankton along the River Loire. Distribution of phytoplankton functional groups coupled with chemical and physical parameters are described at whole river scale (19 stations, between March and November 2009). Natural longitudinal changes were reflected by the switch from benthic Pennales (TB) towards meroplanktic greens (J) via unicellular centric diatoms (D/C). While upstream human pressure was mostly associated to species indicating eutrophic, stagnant environments (coda P, M, H1, Y), downstream attenuation of the Q(r) reflected enriched, shallow environments with prolonged residence time (coda J, X2, X1). Occurrence of minimum Q(r) index values were synchronized to late summer, but the longer was the distance from the source, the earlier was the seasonal decrease of Q(r). Increasing downstream co-dominance of codon F evidenced an ascending light availability in summer. The longitudinal distribution of functional groups allowed us to conclude that functional diversity might be able to sign human-affected richness, while simply species diversity does not.

Characteristics of the pelagic phytoplankton in shallow oxbows

Numerous oxbows of different sizes, depths and ages accompany alluvial rivers in the Carpathian basin. These water bodies provide various habitats for macroscopic and microscopic assemblages. Phytoplankton of 13 oxbows in the Tisza valley was studied between 2005 and 2008. In this article, we focussed on the following questions (i) do the oxbows have unique microflora? (ii) does the macrophyte coverage have a large effect on the composition and biomass of the algal assemblages? and (iii) does the higher plants dominated state result in clear-water conditions in the oxbows? The studied oxbows were in different stages of the ageing process. We classified the sampled oxbows according to their macrophyte vegetation into five types. A total of 646 species of algae were recorded in the oxbows over the study period. The microflora was dominated by cyanophytes, chlorococcalean green algae, euglenophytes and diatom species. Phytoplankton species were allocated into 32 coda. For the determination of typical algal assemblages, we used Kohonen’s Self Organizing Map (SOM) statistical analysis combined with K-means clustering, which has resulted five different types of phytoplankton associations. These types were dominated by coda Y, LO, W1, WS and J. Chlorophyll a data of the sparsely and densely vegetated oxbows did not differ, since a wide range of values characterised both types of the lakes. In this study, the composition of the microflora is similar to that of other eutrophic lakes, but some rarely occurring taxa such as Peridinium gatunense Nygaard and Peridiniopsis elpatiewskyi (Ostenf.) Bourelly might play a key role in the phytoplankton succession of the oxbows. The effect of the macrophyte coverage was decisive in the composition of the algal assemblages, and our investigations indicated that, in the case of the oxbows, the macrophyte-dominated state does not necessarily result in a clear-water state.

Lake stratification in the Carpathian basin and its interesting biological consequences

Abstract Stratification of small temperate lakes of the Carpathian basin was studied. Values of Schmidt stability and Lake Number indicated stable summer stratification. Depending on their depth and wind shelter, the lakes could be characterized by various stratification patterns. A near-linear stratification was observed in the Malom Tisza oxbow where in summer during midday the whole water column belonged to the metalimnion. Mixing of the upper water layer was generated by nocturnal cooling. Stable stratification had pronounced consequences for the vertical distribution of chemical variables and phytoplankton. Concentration of sestonic chlorophyll showed bimodal distribution produced by algae in the upper and purple bacteria in the deeper layers. These results revealed that processes and phenomena associated with deep stratified lakes can be observed in shallow basins.