Abstracts

Water Ecosystems

During summer temperature stratification Shira lake is observed to have a sustainable depth maximum of all species dominating in phytoplankton except for diatoms (Zotina et al., 1999). To verify the hypothesis explaining the mechanism of this phenomenon vertical turbulent diffusion model has been developed. The model includes two species of algae with different light demands and one species of copepods. All of them are biomass-dominant in phyto- and zooplankton of Shira Lake. The model is based on species specific kinetic constants obtained in experiments. Light limitation and inhibition, "predator-prey" and biogenic limitation mechanisms were examined as basic mechanisms, responsible for depth maximum of algae. The depth maximums of light-demanding (green) and dark-demanding (blue-green) algae have been found to be able to form concurrently when both the light-dependent growth of algae and the temperature-dependent growth of copepods and their grazing are considered together. The maximum growth of light-demanding algae corresponds to the maximum growth of copepods. So, the maximum of light-demanding algae forms in the depth beyond the reach of grazers. At the same time the depth maximum of dark-demanding algae forms due to its growth at the depth with low light conditions, which is favourable for them. Addition of phosphorus limitation mechanism decreases the growth rate of algae. It helps the zooplankton to eliminate the light-demanding algae. As a result, the light-demanding algae exhibit the depth maximum when the numbers of the grazer is lower - closer to the numbers of crustaceans in the lake. All calculation versions demonstrate that with time the light-demanding alga is eliminated. The calculated vertical profiles of temperature, phosphorus and light are in good agreement with the field ones.

Zotina T.A., Tolomeyev A.P., Degermendzhy N.N. Lake Shira, a Siberian salt lake: ecosystem structure and function. 1. Major physico-chemical and biological features. // International Journal of Salt Lake Research, 1999, V.8, I.3. – P. 211-232.

Note. Abstracts are published in author's edition

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