№ 6 (2019)

We have developed a modified method of headspace analysis of water samples with the control of temperature and total pressure in the gaseous phase of a closed heterogeneous system followed by a gas chromatographic measurement of methane concentration with the methane content in the lake water of < 500 nl СН₄/L. Here, we describe the background concentrations and vertical distribution of dissolved methane in the water column of Lake Baikal, which were obtained for several years.

The chemical composition and current state of water quality of the Selenga River and its tributaries in Mongolia are considered in this article based on the hydrochemical studies carried out in July 2013-2014. The observed changes in the chemical composition of the water resulted from natural and anthropogenic factors are analyzed. It is shown that water quality of the Selenga River and its tributaries worsened because of the entering of polluting components from the catchment area of Ulaanbaatar city and its wastewater. No influence of the wastewater from the Erdenet Ore-Dressing Plant (EODP) on the trace elements content in the water of the Orkhon and Selenga Rivers is revealed.

The mass development of the phototrophic under-ice community is an interesting phenomenon known for the Arctic Ocean as well as for some rivers and freshwater lakes, including Lake Baikal. Species composition and productive characteristics of the under-ice phytoplankton in Lake Baikal are well studied. During the under-ice blooming, an endemic dinoflagellate Gymnodinium baicalense var. minor Antipova can have more than half of the annual primary phytoplankton production. However, there are still many questions to be answered regarding the factors limiting abundance and proliferation of the under-ice phytoplankton as well as mechanisms facilitating it to persist in Lake Baikal under conditions of the low salinity and low temperature. In present work, we studied the development dynamics of dinoflagellates and microalgae under the ice cover in Listvennichny Bay of Lake Baikal from February to April 2018. Simultaneously, the dynamics of the chemical composition and concentration of atmospheric precipitation were analysed. We observed the under-ice community with the domination of endemic dinoflagellate Gymnodinium baicalense var. minor in April. The biomass of this species considerably varied on different days from 0.04 to 10.0 x 10³ mg/m³. The results of this study indicated that nutrient supply from precipitation could be an important source of nutrition for organisms developing under the ice, in particular, Gymnodinium baicalense var. minor, and could be one of the factors causing the fluctuations in its biomass. We suggested that abrupt significant increases in abundance of G. baicalense var. minor could be a result of their active migration to the area with elevated concentration of nitrogen from atmospheric precipitation. Such an ability may help this species to prosper under the ice of Lake Baikal.