Dynamic Lake Ice Movement on Lake Khovsgol, Mongolia, Revealed by Time Series Displacements from Pixel Offset with Sentinel-2 Optical Images

As one of the most sensitive indicators of global climate change, seasonal ice-covered lakes are attracting gaining attention worldwide. As a large seasonal ice-covered lake located in Northern Mongolia, Lake Khovsgol not only provides important freshwater resources for the local population but also serves as a means of water transportation in summer and an important land-based activity for residents in winter. In this study, we used the sub-pixel offset technique with multi-temporal Sentinel-2 optical images to estimate the time-series displacement of lake ice in Lake Khovsgol from 7 December 2020 to 17 June 2021. With the processing of 112 Sentinel-2 images, we obtained 27 pairs of displacement results at intervals of 5, 10, and 15 days. These lake ice movement results covered three stages from ice-on to ice-off. The first stage was the lake ice growth period, which lasted 26 days from 7 December 2020 to 3 January 2021. Ice formation started from the south and extended northward, with a displacement of up to 10 m in 5 days. The second stage was the active phase of the ice cover, which took place from 3 January 2021 to 18 April 2021. Maximum displacement values reached 12 m in the east and 11 m in the north among all observations. The value of the lake ice movement in the north–south direction (NS) was found to be larger than in the east–west direction (EW). The third stage was the melting period, which closed on 17 June 2021. In comparison to the freezing date of November in past years, our results demonstrate the ice-on date of Lake Khovsgol has been delayed to December, suggesting a possible reason that the seasonal ice-covered lake located at the middle latitude has been affected by global warming. In addition, the lake ice movement of our results can reveal the regional climate characteristic. This study is one of the few cases to reveal the distribution characteristics and changing trends of lake ice on the Mongolia Plateau, providing a rare reference for lake ice research in this region.

Extended Evaluation of Viral Diversity in Lake Baikal through Metagenomics

Lake Baikal is a unique oligotrophic freshwater lake with unusually cold conditions and amazing biological diversity. Studies of the lake's viral communities have begun recently, and their full diversity is not elucidated yet. Here, we performed DNA viral metagenomic analysis on integral samples from four different deep-water and shallow stations of the southern and central basins of the lake. There was a strict distinction of viral communities in areas with different environmental conditions. Comparative analysis with other freshwater lakes revealed the highest similarity of Baikal viromes with those of the Asian lakes Soyang and Biwa. Analysis of new data, together with previously published data allowed us to get a deeper insight into the diversity and functional potential of Baikal viruses; however, the true diversity of Baikal viruses in the lake ecosystem remains still unknown. The new metaviromic data will be useful for future studies of viral composition, distribution, and the dynamics associated with global climatic and anthropogenic impacts on this ecosystem.