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The fate of phytoplankton communities in different hydrological and hydrochemical conditions was studied in the middle basin of the Biebrza River (NE Poland). Our results showed that hydrological connectivity significantly influenced phytoplankton abundance in floodplain lakes: minimal abundance was stated in lotic and maximal in lentic waterbodies. Phytoplankton diversity and species richness were related to changes in water levels. During the low-water phase, phytoplankton biodiversity was the lowest in lentic and the highest in lotic lakes. High water levels promoted exchanges in species among waterbodies and the river, which increased biodiversity indices. We concluded that the isolation of any floodplain lake from the river channel deteriorates its trophic conditions. Thus, the decrease in phytoplankton biodiversity in floodplain lakes should be regarded as an indirect feedback of the hydrobionts on the hydrological factors.
The species composition and size-structure of the phytoplankton community in the Boka Kotorska Bay (SE Adriatic Sea) were analysed with respect to abundance and carbon biomass, together with the physico-chemical parameters, with the aim of evaluating the predefined oligo-mesotrophic status of this transitional water ecosystem. Three stations located in the inner part of the Bay were sampled with seasonal frequency in 2008/2009. Picophytoplankton cells were counted using flow cytometry; nanophytoplankton and microphytoplankton were identified and counted by light microscopy. The relative importance of the picoplankton in the Bay, in terms of both abundance and biomass, during all the investigated seasons emphasized their significance in the phytoplankton community. Picocyanobacteria (Synechococcus) constituted a significant part of the summer assemblages with regard to both abundance (up to 3.38 × 108 cells L−1) and carbon biomass (up to 73% of total phytoplankton carbon). The contribution of the nanophytoplankton was found to be generally low (<20% of the total phytoplankton carbon) in all seasons, and was dominated by autotrophic/mixotrophic flagellates. Species with a preference towards nutrient-enriched conditions, like the diatom Skeletonema marinoi, dominated the microphytoplankton fraction. S. marinoi was the most abundant in spring/winter (up to 2.86×106 cells L−1) above the halocline (making a 96% contribution to the microphytoplankton). The potentially toxin-producing diatom Pseudo-nitzschia pseudodelicatissima was recorded at abundances greater than 105 cells L−1, together with Thalassionema frauenfeldii, as well as the dinoflagellates Prorocentrum micans and the potentially harmful P. minimum. The higher values of phytoplankton biomass and the dominance of phytoplankton species or groups with preferences for nutrient-enriched conditions appear to be consistent with the oligo-mesotrophic status of this specific ecosystem.
The paper presents the results of a study on allelopathic effect of extracts from Stratiotes aloides on natural lake phytoplankton communities grown outdoor in 40 l containers under natural light conditions. The water and plants were taken from an oxbow lake in spring (when S. aloides plants were submerged) and in summer (when plants were floating on lake water surface). Water extracts were prepared from fresh healthy leaves obtained on both sampling occasions. Control containers were supplemented with N and P in amounts similar to those introduced to experimental containers with macrophyte extracts. That way the experimental set up excluded the possibility of phytoplankton limitation by nutrients. Under such conditions the extracts from S. aloides strongly reduced phytoplankton biomass measured as the concentration of chlorophyll a (from 370 to 141 mg chl. a m⁻³ in spring and from 266 to 50 mg chl. a m⁻³ in summer). The inhibition of phytoplankton growth was indirectly confirmed by higher concentrations of available nutrients in experimental versus control containers. The extracts affected also the spring phytoplankton community structure by selective inhibition of diatoms and, to a less extent, of green algae and Cryptophyceae. Similar response of phytoplankton biomass to extracts obtained from submerged and floating S. aloides might suggest that allelochemicals were the constitutive part of macrophyte tissue and their production was not induced by competition between macrophyte and algae.
The phytoplankton in a lowland dam reservoir was studied in the third and fourth year after filling. The increasing concentrations of phosphates, ammonium ions and dissolved organic carbon were favourable for the development of blue-green algae. Besides Cyanophyta small green algae occurred in great numbers while in spring and autumn diatoms dominated in the phytoplankton biomass. High average densities in summer (4.5-5 10³ ind. dm-³) and biomass exceeding 8 mg dm-³ suggested that in accordance with the natural characteristics of waters of the peat-forest catchment area, there developed communities typical of eutrophic waters.
Phytoplankton composition and biomass were studied in a small suburban lake within the city of Poznań (western Poland) on the basis of water samples taken in epilimnion. Results obtained in 1999 were compared with the first study period, of 1978. In the first period, 100 phytoplankton taxa were found and diatoms were the largest group of species (29% of all taxa), while in the second period 117 phytoplankton taxa were recorded and green algae dominated (50%). The mean phytoplankton biomass increased nearly 2-fold over the two decades and the trophic state index was higher in 1999. Picophytoplankton, whose seasonal fluctuations were analyzed only in 1999, accounted for 0.6% to 31.5% (mean 12.8%) of total phytoplankton biomass.
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