The break-up of the Soviet Union in 1991 triggered cropland abandonment on a continental scale, which in turn led to carbon accumulation on abandoned land across Eurasia. Previous studies have estimated carbon accumulation rates across Russia based on large-scale modelling. Studies that assess carbon sequestration on abandoned land based on robust field sampling are rare. We investigated soil organic carbon (SOC) stocks using a randomized sampling design along a climatic gradient from forest steppe to Sub-Taiga in Western Siberia (Tyumen Province). In total, SOC contents were sampled on 470 plots across different soil and land-use types. The effect of land use on changes in SOC stock was evaluated, and carbon sequestration rates were calculated for different age stages of abandoned cropland. While land-use type had an effect on carbon accumulation in the topsoil (0-5 cm), no independent land-use effects were found for deeper SOC stocks. Topsoil carbon stocks of grasslands and forests were significantly higher than those of soils managed for crops and under abandoned cropland. SOC increased significantly with time since abandonment. The average carbon sequestration rate for soils of abandoned cropland was 0.66 Mg C ha yr (1-20 years old, 0-5 cm soil depth), which is at the lower end of published estimates for Russia and Siberia. There was a tendency towards SOC saturation on abandoned land as sequestration rates were much higher for recently abandoned (1-10 years old, 1.04 Mg C ha yr ) compared to earlier abandoned crop fields (11-20 years old, 0.26 Mg C ha yr ). Our study confirms the global significance of abandoned cropland in Russia for carbon sequestration. Our findings also suggest that robust regional surveys based on a large number of samples advance model-based continent-wide SOC prediction.

In this study, we compared non‐forested and forested habitat types of a degraded bog in Western Germany with regard to the base cation chemistry of their pore waters. Peat profiles were sampled in 10‐cm intervals every month from April to July 2009 down to a maximal depth of 150 cm. Pore waters were analysed for Ca, Mg, K and Na concentrations. Additionally, electrical conductivity and pH were measured in surface pools. Both habitat types were sampled with four replicate plots, showing the same vegetation structure. Strong differences were found between the concentrations and distributions of base cations in the pore water profiles from the different habitat types. The forested sites revealed higher concentrations for all base cations, but especially for Ca and Mg. Seasonality had an effect on element distributions in pore waters, but its influence was particularly strong at the forested sites. Element distributions and seasonality were caused by several interacting biological and physicochemical processes, such as plant uptake and mineralization or evaporative enrichment and dilution by rainwater. Concludingly, we draw implications for bog restoration and for the use of element ratios as criterion of mineral influence on bog waters. Our study clearly demonstrates the enhancement of base cation supply by birch encroachment, which is posing an additional burden on successful bog restoration. Additionally, the importance of an intact buffer zone around restored peat bogs is underlined. Copyright © 2013 John Wiley & Sons, Ltd.

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