Habitats of organisms in Lake Baikal have been comprehensively monitored for many years. In 2010–2015, we conducted 8 research expeditions to study ionic composition of the water and measure concentrations of dissolved oxygen, nutrients, organic carbon, and persistent organic pollutants in the entire pelagic area of Lake Baikal. Our data showed that the ionic composition was stable at all depths in the pelagic zone of the lake. We also recorded seasonal variability, vertical stratification, and spatial variations in the content of nutrients, organic matter, and gas components. The concentrations of major ions, nutrients, and dissolved oxygen were favourable for the growth of hydrobionts in the offshore pelagic zone. Concentrations of pollutants in Lake Baikal, such as persistent organic pollutants and heavy metals, were low and did not directly affect the biota. The water in specific areas of the littoral zone of Lake Baikal, however, was polluted near large settlements (Listvyanka, Severobaikalsk, Baikalsk, and Slyudyanka) and in bays because of unsatisfactory operations of sewage treatment plants, growing tourist activity, and intense ship traffic. Continuing investigations are needed to elucidate causes of eutrophication in the littoral zone of Lake Baikal.

Polycyclic aromatic hydrocarbons (PAHs) were detected in different types of PAH-containing samples collected in Lake Baikal during wildfires in the adjacent areas. The set of studied samples included the following: (i) water from the upper layer (5 m); (ii) water from the surface microlayer; (iii) water from the lake tributaries; (iv) water from deep layers (400 m); and (v) aerosol from the near-water layer. Ten PAHs were detected in the water samples: naphthalene, 1-methylnaphthalene, 2-methylnaphthalene acenaphthylene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, and chrysene. The total PAH concentrations (ƩPAHs) were detected in a wide range from 9.3 to 160 ng/L, characterizing by seasonal, intersessional, and spatial variability. In September 2016, the ƩPAH concentration in the southern basin of the lake reached 610 ng/L in the upper water layer due to an increase in fluorene, phenanthrene, fluoranthene, and pyrene in the composition of the PAHs. In June 2019, ƩPAHs in the water from the northern basin of the lake reached 290 ng/L, with the naphthalene and phenanthrene concentrations up to 170 ng/L and 92 ng/L, respectively. The calculation of back trajectories of the atmospheric transport near Lake Baikal, satellite images, and ƩPAH concentrations in the surface water microlayer of 150 to 960 ng/L confirm the impact of wildfires on Lake Baikal, with which the seasonal increase in the ƩPAH concentrations was associated in 2016 and 2019. The toxicity of PAHs detected in the water of the lake in extreme situations was characterized by the total value of the toxic equivalent for PAHs ranging from 0.17 to 0.22 ng/L, and a possible ecological risk of the impact on biota was assessed as moderate.

The article analyzes the chemical composition (ions, elements, and polycyclic aromatic hydrocarbons) of the atmospheric aerosol in the near-water layer of the atmosphere above Lake Baikal during wildfires in Siberia. Aerosol deposition affects the aquatic environment of the watershed basin and the lake itself. The current law on Lake Baikal limits the activity of the permanent stationary anthropogenic sources of the aerosol in the central ecological zone, and they do not have a significant negative impact. Wildfires can have a much greater impact on the environment. Smoke emissions entering the area of Lake Baikal due to wildfires change the chemical properties of the atmospheric aerosol and increase its mass and number concentration. The concentrations of NH₄⁺, K⁺, NO₃⁻, and SO₄²⁻, which enter with submicron aerosol fraction, increase in the ionic composition of the aerosol. The composition of polyaromatic compounds changes, and their concentrations increase. Elevated concentrations of B, Mn, Zn, As, Sr, Cd, and Pb in the composition of aerosol indicate the influx of air masses from the areas prone to wildfires. Despite the sporadic effects of these natural factors, they affect the pollution of various Baikal ecosystems, especially small tributaries of the lake, whose main supply is atmospheric.

The paper presents the results of studies of the content of particulate matter PM₁–PM₁₀ in the atmosphere of the western coast of Southern Baikal with high temporal resolution. It has been established that PM are emitted into the atmosphere of Southern Baikal from both anthropogenic and natural sources. In winter, the influence of thermal power facilities increases, as evidenced by synchronous increases in the concentrations of submicron aerosol PM₁ and sulfur dioxide. In summer, remote forest fires make a significant contribution to atmospheric pollution with particulate matter. The relationship between the increase in the concentration of PM₁ in the atmosphere in the region under study and mesometeorological features (temperature inversions and mesoscale transfer of plumes from large thermal power plants) has been revealed. Increases in PM₁ concentrations in most cases occur during the night and morning hours, which is associated with a decrease in the thickness of the atmospheric boundary layer.

This paper analyzes the results of the automatic (in situ) recording of the regional transport of pollutants from the large regional coal-fired thermal power plants in the atmospheric boundary layer above the southern basin of Lake Baikal. Due to high stacks (about 200 m), emissions from large thermal power plants rise to the altitudes of several hundreds of meters and spread over long distances from their source by tens and hundreds of kilometers. The continuous automatic monitoring of the atmosphere in the southern basin of Lake Baikal on top of the coastal hill (200 m above the lake) revealed the transport of a large number of sulfur oxides and nitrogen oxides in the form of high-altitude plumes from thermal power plants of the large cities located 70 to 100 km to the northwest of the lake (Irkutsk and Angarsk). The consequence of such transport is the increased acidity of precipitation in the southern basin of Lake Baikal and the additional influx of biogenic nitrogen compounds to the lake ecosystem. The spatial scale and possible risks of such regional transport of air pollution for the lake ecosystem require further closer study.