Climate change may cause increasing tree cover in boreal peatlands, and the impacts of this encroachment will be noted first at forested-to-open bog ecotones. We investigate key metrics of ecosystem function in five such ecotones at a peatland complex in Western Siberia. Stratigraphic analysis of three cores from one of these transects shows that the ecotone has been dynamic over time with evidence for recent expansion of forested peatland. We observed that the two alternative states for northern boreal peatlands (forested/open) clearly support distinct plant and microbial communities. These in turn drive and respond to a number of feedback mechanisms. This has led to steep ecological gradients across the ecotones. Tree cover was associated with lower water tables and pH, along with higher bulk density, aquatic carbon concentrations, and electrical conductivity. We propose that the conditions found in the forested peatland of Western Siberia make the carbon sink more vulnerable to warmer and drier conditions.

The peatlands of the West Siberian Lowlands, comprising the largest pristine peatland area of the world, have not previously been covered by continuous measurement and monitoring programs. The response of peatlands to climate change occurs over several decades. This paper summarizes the results of peatland carbon balance studies collected over ten years at the Mukhrino field station (Mukhrino FS, MFS) operating in the Middle Taiga Zone of Western Siberia. A multiscale approach was applied for the investigations of peatland carbon cycling. Carbon dioxide fluxes at the local scale studied using the chamber method showed net accumulation with rates from 110, to 57.8 gC m⁻² at the Sphagnum hollow site. Net CO₂ fluxes at the pine-dwarf shrubs-Sphagnum ridge varied from negative (−32.1 gC m⁻² in 2019) to positive (13.4 gC m⁻² in 2017). The cumulative May-August net ecosystem exchange (NEE) from eddy-covariance (EC) measurements at the ecosystem scale was −202 gC m⁻² in 2015, due to the impact of photosynthesis of pine trees which was not registered by the chamber method. The net annual accumulation of carbon in the live part of mosses was estimated at 24–190 gC m⁻² depending on the Sphagnum moss species. Long-term carbon accumulation rates obtained by radiocarbon analysis ranged from 28.5 to 57.2 gC m⁻² yr⁻¹, with local extremes of up to 176.2 gC m⁻² yr⁻¹. The obtained estimates of various carbon fluxes using EC and chamber methods, the accounting for Sphagnum growth and decomposition, and long-term peat accumulation provided information about the functioning of the peatland ecosystems at different spatial and temporal scales. Multiscale carbon flux monitoring reveals useful new information for forecasting the response of northern peatland carbon cycles to climatic changes.

Net Ecosystem Exchange, Gross Primary Production And Ecosystem Respiration In Ridge-Hollow Complex At Mukhrino Bog

This article provides a historical review of the peatlands study in the Middle and South taiga, as well as Subtaiga zone of Western Siberia, and summarizes the data on the structure of peat deposits in mires of the region, accumulated by the senior author over many years of field research (1980-2004). The features of the main types of stratigraphic structure, as well as a description of the development history of peat mires, are given based on a detailed study of macrofossil composition of peat cores and peat sections. Peat cores were selected within the landscape-ecological profiles, covering all relief elements from the raised bogs of the watershed plains to the mires of river valleys and gullies of ancient water runoff in different climatic zones and subzones (Subtaiga, Southern taiga and Middle taiga). The oldest peat deposits are associated with the deep thalwegs and ancient hydrological system. Peat formation started simultaneously within the taiga zone and the present subarctic zone of Western Siberia and reached the high distribution level in Boreal period. The peatlands development process tightly followed the climate humidity in the wet periods, the watershed mires actively developed and floodplain mires development was constrained by the alluvial deposition process; in the dry periods, the floodplain mires developed actively and the watershed mires grow was stagnated.

We studied the peat stratigraphy of the Mukhrino peatland, which is a typical ombrotrophic bog for the Middle Taiga zone of Western Siberia, to gain insights into its history, hydrology, and carbon fluxes. For the first time in Western Siberia, seven cores were collected from locations that were chosen to represent the typical present-day vegetation types, and this was performed for the dating of the separated dissolved (DOC) and particulate organic carbon (POC) fractions, which were determined using the Accelerator Mass Spectrometer (AMS) radiocarbon (${}^{14}$C) method. The oldest peat was found at the bottoms of an underlying lake (10,053 cal. year BP) and an ancient riverbed (10,989 cal. year BP). For the whole history of the peatland, the average peat accumulation rate was estimated to be 0.067 ± 0.018 cm yr${}^{-1}$ (ranging from 0.013 to 0.332 cm yr${}^{-1}$), and the carbon accumulation rate was 38.56 ± 12.21 g m${}^{-2}$ yr${}^{-1}$ (ranging from 28.46 to 57.91 g m${}^{-2}$ yr${}^{-1}$). There were clear age differences between the separated samples of the DOC and POC. The DOC was older than the POC in the uppermost 150 cm of the peat deposit and younger in the deeper layers. The difference in age increased with depth, reaching 2000–3000 years at the bottom of the peat deposit (depth of 430–530 cm). Following the consideration of a range of factors that could potentially cause the dating discrepancy, we hypothesised that the DOC continuously moves down into the mineral sediment beneath the peat, as an additional carbon flux that results in the mixing of younger and older carbon. On this basis, we estimated the apparent rate of the DOC’s downward movement and the associated rate of carbon loss. The first estimate of the average rate of the DOC’s downward movement in Western Siberia was 0.047 ± 0.019 cm yr${}^{-1}$, causing carbon loss in the range of 28–404 mg m${}^{-2}$ yr${}^{-1}$.