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1

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

Lenard T.

Oceanological and Hydrobiological Studies

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2015

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Vol. 44, No. 2

164--171

EN

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.

2

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

Wojciechowska W., Lenard T.

Oceanological and Hydrobiological Studies

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2014

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Vol. 43, No. 2

147--153

EN

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.

3

Trophic State of a Shallow Lake with Reduced Inflow of Surface Water

Ejankowski W., Lenard T.

Archives of Environmental Protection

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2014

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Vol. 40, no. 3

3--11

EN

According to the general classification of shallow eutrophic lakes, two alternative types are distinguished: phytoplankton-dominated and macrophyte-dominated lakes. The latter type is rare and currently endangered by human activity. In order to determine the effect of reduced inflow of surface water by an earth dyke on the lake trophic state, certain biological and physico-chemical parameters were evaluated. This work focuses on two lakes of similar morphometric characteristics situated in the agricultural landscape. The effect of the earth dyke on the trophic state was positively verified. The lake situated in the catchment basin, in which the inflow of surface water was reduced, was defined as meso-eutrophic, with a small amount of phytoplankton and high water transparency. The reference lake was highly eutrophic, with low water transparency and a large amount of phytoplankton. The water body surrounded by the earth dyke was macrophytes dominated (65% of the lake area), whereas the reference lake was a phytoplankton-macrophyte type (42% of the lake area). The trophic evaluation of a lake can be underestimated because of a significant amount of biogenic compounds accumulated in plant tissues. Thus, the values of Carlson’s indices in macrophyte-dominated lakes may not account for the total amount of nutrients in the water body.

PL

W ogólnej klasyfi kacji płytkich jezior eutrofi cznych można wyróżnić dwa alternatywne typy zbiorników: zdominowane przez fitoplankton i zdominowane przez makrofity. Ten drugi typ jezior jest rzadki i obecnie zagrożony działalnością człowieka. W celu określenia wpływu zredukowanego dopływu wód powierzchniowych przez ziemną groblę na stan troficzny jeziora, poddano ocenie wybrane parametry biologiczne i fizyczno-chemiczne dwóch zbiorników o podobnej morfometrii, położonych w krajobrazie rolniczym. Efekt oddziaływania grobli na jakość ekosystemu jeziornego oceniono jako znaczący. Jezioro położone w zlewni, w której dopływ wód powierzchniowych był ograniczony, zostało zaklasyfikowane jako mezo-eutroficzne, z małą ilością fitoplanktonu i o dużej przezroczystości wody. Jezioro porównawcze było silnie eutroficzne, z dużą ilością fitoplanktonu i o niskiej przezroczystości wody. Zbiornik otoczony przez groblę reprezentował typ makrofitowy (65% powierzchni jeziora pokryta przez roślinność), a stan jeziora porównawczego, w którym roślinność zajmowała 42% misy jeziornej, mieścił się między typem fitoplanktonowym i makrofitowym. Ocena trofii jezior może być jednak niedoszacowana, ponieważ znaczna część nutrientów może być zakumulowana w tkankach roślin. Stąd, wartości wskaźników Carlsona w przypadku jezior makrofitowych mogą nie uwzględniać ogólnej ilości nutrientów w jeziorze.

4

Phytoplankton diversity and biomass during winter with and without ice cover in the context of climate change

Lenard T., Wojciechowska W.

Polish Journal of Ecology

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2013

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Vol. 61, nr 4

739--748

EN

Most scenarios of the predicted climate change in Europe imply that the increasing temperature trend will be maintained in winter seasons. The presence or absence of the ice cover in winter can impact on the functioning of lake ecosystems. The research was carried out in two mesotrophic and dimictic lakes in winter with and without ice cover. The biomass and phytoplankton and its composition was analysed with reference to physical factors (PAR and temperature). The research proved that poor thermal-light conditions under the ice/snow cover favoured the development of nanoplanktonic species from the genus Cryptomonas (Cryptophyta) or Stephanodiscus (Bacillariophyceae), whereas microplanktonic species of dinoflagellates, diatoms or green algae prevailed during the ice-free winter. The highest phytoplankton biomass and species richness were recorded during ice-free winter, which affected a higher Shannon-Wiener diversity index and evenness. It has been shown that the mild winter creates good conditions for the development of phytoplankton species characteristic for the mixing periods. The lack of inverse thermal stratification during winter can lead to disturbance in the functioning of the water ecosystems throughout the year.