The effect of extreme rainfall on summer succession and vertical distribution of phytoplankton in a lacustrine part of a eutrophic reservoir

Abstract

During the summer of 2006, phytoplankton succession and vertical distribution were studied in the eutrophic Ř ímov Reservoir (Czech Republic). Disturbances in the form of dramatic summer storms had a crucial effect on phytoplankton succession and its vertical distribution. Two extreme rainfalls substantially increased flushing rate, yielding a fairly short retention time within the reservoir that disrupted established thermal stratification. The first storm initiated the development of summer phytoplankton, while the second storm reversed the phytoplankton succession to an earlier stage. The measurement of vertical profiles of chlorophyll a showed that the phytoplankton were heterogeneously distributed in the water column and formed subsurface diatom maxima (SDM) over most of the summer. Biogenic silica deposition studied by PDMPO (2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamyl)-methoxy] phenyl}oxazole) was measured to compare diatom growth rates over the season and between surface and depth of SDM. Diatoms deposited 20 times more silica at the surface than at the SDM depth, although only a half of diatom population was involved in the silica deposition. Maximum rates of silica deposition were measured in samples just after both summer storms events. When diatoms dominated the phytoplankton, the amounts of available Si and P in water were significantly correlated (r 2 = 0.81, p < 0.001, df = 42). Outliers from the linear relationship were found only during a period when substantial picocyanobacterial population developed in the reservoir. Due to their lack of Si requirements, ambient Si concentration markedly increased while P was depleted to growth limiting levels. Temporal variations in Si:P ratio therefore illustrate the importance of resource competition in phytoplankton seasonal succession.

Do current European lake monitoring programmes reliably estimate phytoplankton community changes?

“…In particular, cyanobacteria are favoured by heat wave conditions (Jöhnk et al, 2008). Contrary to heat waves, which are characterised by increases in water column stability, heavy rain events increase flushing rates and therefore nutrient loads into the lake, stimulating phytoplankton growth, but heavy rain may also reduce phytoplankton biomass due to removal or dilution (Znachor et al, 2008).…”

Patterns of asynchrony for phytoplankton fluctuations from reservoir mainstream to a tributary bay in a giant dendritic reservoir (Three Gorges Reservoir, China)

“…Numerous physical (e.g., light availability, mixing regime) and chemical (nutrient concentrations) factors have shown pronounced longitudinal changes from the riverine zone to the lacustrine zone, which promote the occurrence of spatial heterogeneity of phytoplankton in reservoirs (Nogueira 2000;Mašín et al 2003;Sthapit et al 2008). On the other hand, reservoirs are subject to high temporal variability in habitat conditions, with frequent reorganization of phytoplankton abundance and species composition, as a result of the interactions between various physical, chemical and biological factors (Calijuri et al 2002;Simek et al 2008;Znachor et al 2008). Temporal fluctuations of phytoplankton have thus been regarded as one notable characteristic of the reservoir ecosystem.…”

Different effects of planktonic invertebrate predators and fish on the plankton community in experimental mesocosms

“…The increase in a mixed group of chromophytes and dinophytes (Fig. 2D) at the end of the experiment was likely associated with the development of the early summer population of the diatom Fragilaria crotonensis, which recurrently dominates the summer phytoplankton along with filamentous and colonial cyanobacteria (Znachor et al, 2008).…”