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Winter bloom of some motile phytoplankton under ice cover in a mesotrophic lake : vertical distribution and environmental factors

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Lenard T.

Oceanological and Hydrobiological Studies

2015

tom Vol. 44, No. 2

164--171

The research was carried out in mesotrophic Lake Krasne during winter with thick ice/snow cover. Water samples for biological and physicochemical analyses were collected vertically from the water column. Several phytoplankton groups were identified during the study, however, only two main groups of motile phytoplankton, Cyanophyceae (the dominant species − Planktothrix rubescens) and Cryptophyceae (Cryptomonas spp. and Plagioselmis nannoplanctica), were analyzed in the gradient of nutrients, light and thermal conditions. In the studied water column, values of physicochemical parameters did not vary in a wide range. Nevertheless, high discrepancies were noted in the values of phytoplankton biomass and the concentration of chlorophyll-a which had shallower maxima and deeper minima. Statistically significant relationships were found between the biomass of two main phytoplankton groups, light conditions (PAR) and depth, however, no significant relationships were found between the biomass, biogenic compounds and water temperature. The studies showed that in the winter season with ice/snow cover, cryptomonads and Planktothrix rubescens occupied different ecological niches and the main factor determining their distribution were light conditions. The ice/snow cover probably plays an important role in protection of P. rubescens winter filaments against photoinhibition.

Effect of extremely severe winters on under-ice phytoplankton development in a mesotrophic lake (Eastern Poland)

75%

Wojciechowska W. , Lenard T.

Oceanological and Hydrobiological Studies

2014

tom Vol. 43, No. 2

147--153

The research was carried out in a mesotrophic and dimictic lake during winters with ice cover. In the last forty years, the development of phytoplankton was analyzed in five extreme winter seasons. The studies of phytoplankton characteristics in the water column took into account values of biomass, concentration of chlorophyll-a and species composition, including dominant species. Differences in the vertical distribution of flagellate and non-flagellate species belonging to cyanobacteria and algae were analyzed in the gradient of light and thermal conditions. The phytoplankton biomass was low and vertically differentiated, with the lowest values at the deeper part of the water column. Flagellate species from the group of Cryptophyceae, Chrysophyceae and Dinophyceae were most abundant. Species biodiversity was low but every winter the dominant species represented different taxonomic groups. In some periods, larger non-motile phytoplankton species from green or blue-green algae dominated. The research proved that the development of phytoplankton under the ice cover was limited mainly by light and, to a lesser extent, by temperature.