Mikhail A. Korets

The West Siberian Lowland (WSL) contains some of the largest wetlands and most extensive peatlands on Earth, storing vast amounts of vulnerable carbon across permafrost‐free to continuous permafrost zones. As temperature and precipitation changes continue to alter the Siberian landscape, carbon transfer to the atmosphere and export to the Arctic Ocean will be impacted. However, the drivers of organic carbon transfer are largely unknown across this region. We characterized seasonal dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition of WSL rivers from the middle reaches of the Ob’ River in the permafrost‐free zone, as well as tributaries of the Taz River in the northern continuous permafrost zone. DOC and aromatic DOM properties increased from spring to autumn in the Ob’ tributaries, reflecting the seasonal transition from groundwater‐sourced to terrestrial DOM. Differences in molecular‐level signatures via ultra‐high resolution mass spectrometry revealed the influence of redox processes on DOM composition in the winter while terrestrial DOM sourcing shifted from surface litter aliphatics and highly unsaturated and phenolic high‐O/C (HUP_{High O/C}) compounds in the spring to subsurface soils and HUP_{Low O/C} compounds by autumn. Furthermore, aromaticity and organic N were related to landscape properties including peatlands, forest cover, and the ratio of needleleaf:broadleaf forests. Finally, the Taz River tributaries were similar to summer and autumn Ob’ tributaries, but more enriched in N and S‐containing compounds. These signatures were likely derived from thawing permafrost, which we expect to increase in northern rivers due to active layer expansion in a warming Arctic.

Understanding how pollen assemblages represent the local and regional vegetation composition is crucial for palaeoecological research. Here, we analyze 102 surface moss/soil pollen samples collected from four study regions located in various boreal forest vegetation types in Central Siberia. Despite Larix being the most prevalent tree generus in the study area, the proportion of Larix pollen can be as low as 0.6–1.5% (0.4–4.7% on average) even in localities with a high canopy density of the species. No relationship between the quantity of Larix pollen in the spectra and the abundance of Larix in the local vegetation was found. The dominant components of the pollen assemblages are Betula and Alnus fruticosa. The pollen value of Picea is low (2.6–8.2% on average), with higher proportions at sample plots where spruce is abundant in forests. Pinus is a highly prevalent pollen species within its geographical range, comprising up to 40% of pollen assemblages. Outside of the range, the ratio of Pinus pollen was higher in habitats with low canopy density and in treeless ecosystems. The composition of herbaceous pollen and spores is significantly affected by the local plant community, offering more comprehensive insights into past vegetation patterns.

Increased warming in the Arctic is of great concern. This is particularly due to permafrost degradation, which is expected to accelerate microbial breakdown of soil organic carbon, with its further release into the atmosphere as carbon dioxide (CO₂). The fine-scale variability of CO₂ fluxes across highly mosaic Arctic tundra landscapes can provide us with insights into the diverse responses of individual plant communities to environmental change. In the paper, we contribute to filling existing gaps by investigating the variability of CO₂ flux rates within different landscape units for dominant vegetation communities and plant species across typical tundra of the southern part of the Taimyr Peninsula, Siberia. In general, the variability of soil CO₂ flux illustrates a four-fold increase from non-vascular vegetation, mainly lichens and mosses (1.05 ± 0.36 µmol m⁻² s⁻¹), towards vascular plants (3.59 ± 0.51 µmol m⁻² s⁻¹). Barren ground (“frost boils”) shows the lowest value of 0.79 ± 0.21 µmol m⁻² s⁻¹, while considering the Arctic “browning” phenomenon, a further substantial increase of CO₂ flux can be expected with shrub expansion. Given the high correlation with top soil temperature, well-drained and relatively dry habitats such as barren ground and non-vascular vegetation are expected to be the most sensitive to the observed and projected temperature growth in the Arctic. For mixed vegetation and vascular species that favor wetter conditions, soil moisture appears to play a greater role. Based on the modeled seasonal pattern of soil CO₂ flux and precipitation records, and applying the rainfall simulations in situ we outlined the role of precipitation across enhanced CO₂ emissions (i.e., the “Birch” effect). We found that a pulse-like growth of soil CO₂ fluxes, observed within the first few minutes after rainfall on vegetated plots, reaches 0.99 ± 0.48 µmol m⁻² s⁻¹ per each 1 mm of precipitation, while barren ground shows 55–70% inhibition of CO₂ emission during the first several hours. An average additive effect of precipitation on soil CO₂ flux may achieve 7–12% over the entire growing season, while the projected increased precipitation regime in the Arctic may strengthen the total CO₂ release from the soil surface to the atmosphere during the growing season.

This paper presents a technique for mapping the vegetation cover of mountainous areas based on seasonal satellite data from Landsat-OLI 8, using information about vegetation growth conditions. This mapping is based on the creation of a layer of relatively homogeneous areas in terms of relief and climate. Training samples for the classification of images were formed within these areas. Satellite images were classified using the maximum likelihood method. The created map reflects the spatial distribution of 9 classes of forest vegetation and 10 classes of non-forest vegetation.

Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-sized rivers (50 000–300 000 km² watershed area) remain poorly known. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94 000 km²), which drains through pristine taiga forest of the boreal zone in the West Siberian Lowland (WSL). We combined continuous and discrete measurements of carbon dioxide (CO₂) concentration using submersible CO₂ sensor and floating chamber flux (FCO₂), with methane (CH₄), dissolved organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over an 800 km transect of the Ket River main stem and its 26 tributaries during spring flood (May 2019) and 12 tributaries during summer baseflow (end of August–beginning of September 2019). The partial pressure of CO₂ (pCO₂) was lower and less variable in the main stem (2000 to 2500 µatm) compared to that in the tributaries (2000 to 5000 µatm). In the tributaries, the pCO₂ was 40 % higher during baseflow compared to spring flood, whereas in the main stem, it did not vary significantly across the seasons. The methane concentration in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 times lower than that of CO₂ and ranged from 0.05 to 2.0 µmol L⁻¹. The FCO₂ ranged from 0.4 to 2.4 g C m⁻² d⁻¹ in the main channel and from 0.5 to 5.0 g C m⁻² d⁻¹ in the tributaries, being highest during August in the tributaries and weakly dependent on the season in the main channel. During summer baseflow, the DOC aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO₂ concentrations and fluxes. We hypothesize that relatively low spatial and seasonal variability in FCO₂ of the Ket River is due to a flat homogeneous landscape (bogs and taiga forest) that results in long water residence times and stable input of allochthonous dissolved organic matter (DOM), which dominate the FCO₂. The open water period (May to October) C emission from the fluvial network (main stem and tributaries) of the Ket River was estimated to 127 ± 11 Gg C yr⁻¹, which is lower than the downstream dissolved and particulate C export during the same period. The estimated fluvial C emissions are highly conservative and contain uncertainties linked to ignoring hotspots and hot moments of emissions, notably in the floodplain zone. This stresses the need to improve the temporal resolution of FCO₂ and water coverage across seasons and emphasizes the important role of WSL rivers in the release of CO₂ into the atmosphere.

Methods of creating information databases for predicting the behavior of vegetation fires are analyzed. A brief description is given of the developed classification of vegetation fuels (VF), which is based on long-term fundamental pyrological research conducted in various regions of Russia. Examples of information databases have been created. The results of using the developed software for making VF maps based on forest inventory data in GIS and for fire behavior prediction are presented. Successful retrospective software performance tests have been carried out using the data of 125 wildfires in plain conditions and 10 wildfires in mountain conditions. A field performance test of the software is planned on active wildfires in the most fire-prone region of Siberia.