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Understanding the mechanisms of blooming of phytoplankton in Lake Shira, a saline lake in Siberia (the Republic of Khakasia)
Degermendzhy, A.G.; Gulati, R.D. (2002). Understanding the mechanisms of blooming of phytoplankton in Lake Shira, a saline lake in Siberia (the Republic of Khakasia). Aquat. Ecol. 36(2): 331-340
In: Aquatic Ecology. Springer: Dordrecht; London; Boston. ISSN 1386-2588, more
Peer reviewed article  

Available in Authors 

Keywords
    Hydrogen sulphide; Mathematical models; Meromictic lakes; Stratification; Cyanobacteria [WoRMS]; PNE, Russia, Siberia

Authors  Top 
  • Degermendzhy, A.G.
  • Gulati, R.D.

Abstract
    The paper summarises the results of a three-year research study (European Union Grant: INTAS 97-O519) aimed at investigating the planktonic populations and trophic organization of the Lake Shira ecosystem - a saline lake in Khakasia, Siberia. The lake exhibits a stable summer-autumn stratification of the chemical-biological components. The mechanisms responsible for the ‘blooming' of phytoplankton in the deeper layers were investigated in greater detail, using data from both field and laboratory experiments. The spectra of nutrition were examined to estimate the relationships between the specific growth rates of the hydrobionts and the influence of the limiting factors: light, nutrients. The observed heterotrophic capability of a metalimnetic phytoplankton population might help explain the development in the deeper waters of Lyngbya contorta. The scheme of trophic interactions was put up, based on the assessment of the carbon pools and carbon flows in the pelagic zone of the lake. A mathematical model of the vertical structure of the lake's plankton populations was constructed, using the ecosystem description and data of vertical turbulent diffusion. The role of light and nutrient limitations and grazing mortality in forming the vertical inhomogeneities, particularly in lowering the depth of the maximal cyanobacterial biomass, has been demonstrated. The theoretical curves for the stratification of chemical and biological parameters have been brought in conformity with the field observations, e.g. for the different patterns of the peaks, and for the biomass maxima of cyanobacteria, purple and green sulphur bacteria, oxygen, and hydrogen sulphide. The calculations revealed that for an adequate assessment of the parameters for the hydrogen sulphide zone it is necessary to introduce flows of allochthonous organic matter. Based on the form of the sulphur distribution curve, the allochthonous input of organic matter and the inflow of hydrogen sulphide from the bottom have been theoretically discriminated for the first time. It has also been ascertained that irrespective of the depth the allochthonous substances limiting bacterial growth, the bacteria are uniformly distributed over depth and can serve as an indicator of the presence of limitation (the effect of autostabilisation in space). Of indisputable interest to limnology are the specific methods developed for understanding the functioning of Lake Shira ecosystem. These include the autostabilisation of the limiting factors, the on-the-spot fluorescent method of determining the three classes of microalgae, the algal mixotrophy and the planktonic population interactions and feedbacks, and development of a more sensitive, bioluminescent method for mapping the non-homogeneities. Owing to a balanced combination of classical approaches (field observations, in situ data on production-decomposition) and the more recent ones (satellite monitoring, biophysical methods of estimating interactions of populations, mathematical models based on the field and experimental data), many of the structural-function relationships in the ecosystem can now be explained, and the models can provide ‘mutual control and mutual agreement' between the data collected using different approaches.

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