The structure of winter phytoplankton in Lake Nero, Russia, a hypertrophic lake dominated by Planktothrix-like Cyanobacteria

Abstract

BackgroundThe permanent dominance of Planktothrix-like сyanobacteria has been often reported for shallow eutrophic\hypertrophic lakes in central Europe in summer\autumn. However studies on phytoplankton growth under ice cover in nutrient-rich lakes are very scarce. Lake Nero provides a good example of the contrasting seasonal extremes in environmental conditions. Moreover, the ecosystem underwent a catastrophic transition from eutrophic to hypertrophic 2003–05, with dominance of filamentous cyanobacteria in summer\autumn. Towards the end of the period of ice cover, there is an almost complete lack of light and oxygen but abundance in nutrients, especially ammonium nitrogen, soluble reactive phosphorus and total phosphorus in lake Nero. The aim of the present study was to describe species composition and abundance of the phytoplankton, in relation to the abiotic properties of the habitat to the end of winters 1999–2010. We were interested if Planktothrix-like сyanobacteria kept their dominant role under the ice conditions or only survived, and how did the under-ice phytoplankton community differ from year to year.ResultsSamples collected contained 172 algal taxa of sub-generic rank. Abundance of phytoplankton varied widely from very low to the bloom level. Cyanobacteria (Limnothrix, Pseudanabaena, Planktothrix) were present in all winter samples but did not always dominate. Favourable conditions included low winter temperature, thicker ice, almost complete lack of oxygen and high ammonium concentration. Flagellates belonging to Euglenophyta and Cryptophyta dominated in warmer winters, when phosphorus concentrations increased.ConclusionA full picture of algal succession in the lake may be obtained only if systematic winter observations are taken into account. Nearly anoxic conditions, severe light deficiency and high concentration of biogenic elements present a highly selective environment for phytoplankton. Hypertrophic water bodies of moderate zone covered by ice in winter and dominated by Planktothrix - like сyanobacteria in summer/autumn may follow several scenarios in the end of winter. It may be intense proliferation сyanobacteria normally dominating in summer, or the switch to the other species like the euglenoids and cryptomonads flagellates, or almost total depletion of phytoplankton.

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

“…In winter 1971 and 2010, small flagellates from the genus Cryptomonas had high contribution in the phytoplankton biomass under the ice cover, and they were present in the whole studied water column. These species can grow under a thick ice cover and despite extremely low values of light and temperature, they are able to cause under-ice blooms (Phillips, Fawley 2002a,b;Babanazarova et al 2013). Periodically (January and March 2006), other flagellate species -Mallomonas akrokomos (Chrysophyceae) − occurred in large numbers beneath the ice of Lake Piaseczno.…”

“…Also Peridinium bipes (Dinophyceae) was an important component of the phytoplankton community in 2003 and 2010 with the highest biomass in the water layer immediately beneath the ice cover. Development of the species from the genus Peridinium and their temporary high contribution in the winter phytoplankton biomass in lakes of different trophic status is very common (Danilov, Ekelund 2001;Philips, Fawley 2002a;Babanazarova et al 2013).…”

“…Relatively high biomass of filamentous cyanophytes in lakes during winters with ice cover can be caused by their already high biomass during the preceding autumn. Moreover, due to their shade tolerance, cyanophytes can grow in conditions of low irradiance and short day, which are typical in cold winters under the ice cover (Reynolds 2006;Babanazarova et al 2013).…”

“…The dominance of some diatom species during winter is partly justified by their abilities to produce special proteins, which help them to survive at low temperatures (Richardson et al 2000). Similarly, some filamentous blue-green algae are adapted to low thermal-light conditions and they can be present in large numbers or even cause under-ice blooms (McKnight et al 2000;Dokulil, Herzig 2009;Babanazarova et al 2013).…”

Interrelationship between nutrients and chlorophyll-a in an urban stormwater lake during the ice-covered period

“…High species diversity has been found under ice despite unfavorable conditions, including limited light availability, low water temperatures, restricted air-water gas exchange and prevention of wind-induced mixing (Salonen et al, 2009, Schröder, 2013. The concentration of nutrients and dissolved organic carbon may help to drive the plankton dynamics (Babanazarova et al, 2013). Griffiths et al (2017) examined the shifts in diatom assemblages from ten High Arctic lakes, lakes and concluded that ice cover is likely the principle driver of some of the most important ecological changes, resulting in increased diversity and the emergence of novel growth forms and epiphytic species.…”