Continuous monitoring of ice cover belongs to the key tasks of modern climate research, providing up-to-date information on climate change in cold regions. While a strong advance in ice monitoring worldwide has been provided by the recent development of remote sensing methods, quantification of seasonal ice cover is impossible without on-site autonomous measurements of the mass and heat budget. In the present study, we propose an autonomous monitoring system for continuous in situ measuring of vertical temperature distribution in the near-ice air, the ice strata and the under-ice water layer for several months with simultaneous records of solar radiation incoming at the lake surface and passing through the snow and ice covers as well as snow and ice thicknesses. The use of modern miniature analog and digital sensors made it possible to make a compact, energy efficient measurement system with high precision and spatial resolution and characterized by easy deployment and transportation. In particular, the high resolution of the ice thickness probe of 0.05 mm allows to resolve the fine-scale processes occurring in low-flow environments, such as freshwater lakes. Several systems were tested in numerous studies in Lake Baikal and demonstrated a high reliability in deriving the ice heat balance components during ice-covered periods.

An automatic hydro-meteorological station (AHMS) was designed to monitor the littoral zone of Lake Baikal in areas with high anthropogenic pressure. The developed AHMS was installed near the Bolshiye Koty settlement (southern basin). This AHMS is the first experience focused on obtaining the necessary competencies for the development of a monitoring network of the Baikal natural territory. To increase the flexibility of adjustment and repeatability, we developed AHMS as a low-cost modular system. AHMS is equipped with a weather station and sensors measuring water temperature, pH, dissolved oxygen, redox potential, conductivity, chlorophyll-a, and turbidity. This article describes the main AHMS functions (hardware and software) and measures taken to ensure data quality control. We present the results of the first two periods of its operation. The data acquired during this periods have demonstrated that, to obtain accurate measurements and to detect and correct errors that were mainly due to biofouling of the sensors and calibration bias, a correlation between AHMS and laboratory studies is necessary for parameters such as pH and chlorophyll-a. The gained experience should become the basis for the further development of the monitoring network of the Baikal natural territory.

In this study, we present results on fatty acid analysis of phytoplankton of Lake Baikal, the world’s deepest lake, which differs from other lakes by its oceanic features. Since we used a large-mesh net, the net sample phytoplankton were primarily represented by the large elongated diatom Synedra acus. subsp. radians (Kützing) Skabichevskij. The similar algae composition of net samples of spring season phytoplankton collected at different sites of the lake allows us to compare results of the fatty acid analysis of these samples. The phytoplankton diversity of the sedimentation samples was contrary represented by 32 algae species. There are clear changes in the fatty acid composition of net phytoplankton exposed to anthropogenic impacts of varying intensity. The content of polyunsaturated fatty acids in phytoplankton collected from central stations (pelagic stations at a distance of ~10–30 km from the shoreline) without anthropogenic impact was higher by up to 15% than phytoplankton collected from nearshore stations (littoral stations at a distance of ~0.01–0.05 km from the shoreline) and offshore stations (pelagic stations at a distance of ~3 km from the shoreline). The interlaboratory precision of fatty acid determination of phytoplankton is estimated as ≤10%. We found high content of the lipid peroxidation marker (80–340 μg g⁻¹ of dry weight) in phytoplankton from nearshore and offshore stations with intensive anthropogenic impact. In phytoplankton from central stations, we did not find any lipid peroxidation. Determination of unsaturated fatty acids, coupled with analysis of fatty acid peroxidation products, can be used to evaluate the level of anthropogenic impact in terms of ecological health and biodiversity conservation.

This paper is devoted to the study of the mesothermal temperature maximum layer (MTML) in Lake Baikal, which is observed during the period of winter stratification. On the one hand, this is a rather well-known phenomenon; on the other hand, it is not sufficiently studied, although it has a significant impact on the thermal regime in winter and water dynamics during the periods of formation and breakdown of inverse temperature stratification. Our work presents the results of analyzing the spatial and temporal variability of the main MTML parameters and their dependence on hydrometeorological factors. For this purpose, CTD soundings and mooring data obtained in the western part of the southern basin of Lake Baikal in 2000–2022 were analyzed in comparison to ERA5-Land reanalysis. The MTML parameters have noticeable within-season and interannual spatial and temporal variability. This is obviously related to the influence of the processes of vertical turbulent mixing, internal wave action, and current patterns. The analysis of interannual differences revealed four types of behavior of the maximum MTML temperature during the ice season. The influence of wind conditions on the main MTML parameters (maximum MTML temperature, depth of its occurrence, and depth of the upper MTML boundary) was shown not only in the fall, but also in the summer period, when heat accumulation in the Baikal water column takes place. With the increased wind activity in the late fall, the MTML is formed deeper and has lower maximum temperature values. At lower wind activity in the fall, the MTML is closer to the surface and the values of the maximum MTML temperature are higher. A change in wind activity in the summer leads to the opposite effect. In spite of the essential trends over the study period in the dates of the occurrence of hydrological events, no noticeable trends were registered for the maximum MTML temperature, its depth, and the depth of the upper boundary of the MTML.

For continuous monitoring of the vertical distribution of temperature in Lake Baikal, as an indirect measure of dynamic processes, a system of distributed temperature sensors was developed in the Laboratory of Hydrology and Hydrophysics of the Limnological Institute of the SB RAS. The system allows to obtain instant vertical temperature profiles with up to 1 Hz frequency and 1 mK resolution. Additionally, each sensor is equipped with a microheater activated by adressed command to implement the thermanemometric mode of operation, to estimate the velocity of water flows. The pilot sample of the thermistor chain contains 11 temperature sensors located along the depth from 20 to 120 meters with a 10 meters step, and covers the active layer of Lake Baikal with the major changes during the year. The developed thermistor chain was integrated into one of the strings of the BaikalGVD neutrino telescope and connected to the specially developed data logger which placed in the telecommunication spherical module. In this article, we give a brief description of the temperature profiling system and preliminary results of tests in the open Baikal during 2022. The obtained measurement results allowed us to consider the temporal variability of the active layer temperature by analyzing its power spectral density. The developed monitoring system allows obtaining qualitatively new hydrophysical data on the state of the active layer of the pelagic part of Lake Baikal in real time.