No abstract

25While phytoplankton studies on large potamal rivers have increased in number in recent years, upper 26 river sections have received considerably less attention. However, in order to better understand 27 processes that govern the development of dominance of euplanktonic elements in the lower river 28 sections, detailed studies of the upstream areas are necessary. We studied the composition, diversity

Assigning species to functional response groups in phytoplankton ecology reduces the number of functional units, which helps understand the processes that shape diversity and functioning of planktonic assemblages. Although the concept has become widespread in recent years, numerical characterization of the groups’ positions in the niche space remained a challenging task. Using a large river phytoplankton dataset, we characterized the functional groups (FGs) of phytoplankton by their niche position and niche breadth in the niche space defined by the relevant environmental variables using the Outlying Main Index approach. The niche space has been defined primarily by trophic-related (nutrients) and river size-related variables (water residence time, discharge). Although we hypothesized that FGs with central niche position would have wide, while those with marginal niche position have narrow niche breadth, these have not been corroborated by the results. Rather, FGs occurred both with central niche position and intermediate breadth, as well as with marginal niche position and wide breadth. Niche position of several FGs was different from that suggested by their known habitat templates in lakes. Furthermore, we found no significant relationship between niche position and niche breadth, suggesting that the occurrence of FGs in rivers is simultaneously influenced by both niche characteristics.

The impact of cumulative daily solar radiation (CDSR) on the biomass of river phytoplankton (Chl-a) in the growing season was studied using a large dataset of rivers in the Carpathian Basin. The amount of solar radiation was cumulated over the range of 1-60 days. The CDSRChl-a relationship could be described by linear regression and appeared to be significant for almost all watercourses with the exception of rivers with short water residence time. To determine the most relevant time period of CDRS impacting phytoplankton biomass, the slopes of regressions were plotted against the accumulating number of days of light exposure (1-60). Two characteristic shapes were obtained: unimodal for rivers with hard substrate and steady increase for lowland rivers with fine substrate. In both cases, there is an increasing tendency in the slope values with water residence time (WRT). It was demonstrated that CDSR has a pronounced impact on river phytoplankton biomass even in cases when WRT was shorter than the cumulated solar radiation period. These results indicate that development of phytoplankton within the river channel is a complex process in which meroplankton dynamics may have significant impacts. Our results have two implications: First, CDSR cannot be neglected in predictive modelling of riverine phytoplankton biomass. Second, climate models forecast increased drought with subsequently increased CDSR in several regions globally, which may trigger a rise in phytoplankton biomass in light-limited rivers with high nutrient concentrations.

Míg a szabad szemmel látható állat-, illetve növényvilággal kapcsolatos ismeretterjesztés széleskörűvé vált, addig a mikroszkopikus világ tudományos igényű ismeretterjesztő bemutatására kevés példát találni. Hagyományteremtő céllal 2015-ben első alkalommal hirdette meg az Algológus Fórum az „Év Algája” internetes szavazást. A végső szavazásra javasolt három algafaj a Didymosphenia geminata, Haematococcus pluvialis és Prymnesium parvum voltak, melyek közül a Haematococcus pluvialis fajra érkezett a szavazatok döntő többsége. A három faj ökológiai és gazdasági vonatkozásainak, valamint hazai elterjedésük bemutatásán keresztül kívánjuk megmutatni, hogy a mikroszkopikus világ képviselői is kellően színesek és érdekesek lehetnek ahhoz, hogy nagyobb teret kapjanak a tudományos ismeretterjesztésben. Tanulmányunk felhívja a figyelmet az algák vízi ökoszisztémákban betöltött alapvető szerepére, esetleges gazdasági jelentőségükre, valamint a földi élet fenntartásában nélkülözhetetlen szerepükre.