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Abstract: Understanding geocryological characteristics of frozen sediment, such as cryostratigraphy, ice content, and stable isotope ratio of ground ice, is essential to predicting consequences of projected permafrost thaw in response to global warming. These characteristics determine thermokarst extent and controls hydrological regime—and hence vegetation growth—especially in areas of high latitude; it also yields knowledge about the history of changes in the hydrological regime. To obtain these fundamental data, we sampled and analyzed unfrozen and frozen surficial sediments from 18 boreholes down to 1–2.3 m depth at five sites near Chokurdakh, Russia. Profiles of volumetric ice content in upper permafrost excluding wedge ice volume showed large variation, ranging from 40 to 96%, with an average of 75%. This large amount of ground ice was in the form of ice lenses or veins forming well-developed cryostructures, mainly due to freezing of frost-susceptible sediment under water-saturated condition. Our analysis of geocryological characteristics in frozen ground including ice content, cryostratigraphy, soil mechanical characteristics, organic matter content and components, and water stable isotope ratio provided information to reconstruct terrestrial paleo-environments and to estimate the influence of recent maximum thaw depth, microtopography, and flooding upon permafrost development in permafrost regions of NE Russia. [Copyright &y& Elsevier]

A future increase in heavy precipitation events is predicted in boreal regions. An irrigation experiment was conducted in Taiga forest in eastern Siberia to evaluate the effect of heavy precipitation on greenhouse gas ([GHG] CO2, CH4, and N2O) fluxes in the soil. The GHG fluxes on the soil surface were measured using a closed-chamber method and GHG production rates in the mineral soil were estimated using the concentration–gradient method based on Fick’s law. Irrigation water (20 mm day−1) was applied continuously for 6 days (120 mm in total; the same amount as summer precipitation in this region). Greenhouse gas production rates in the organic layer (O-layer) were defined as the difference between the GHG fluxes and the GHG production rates in the mineral soil. Carbon dioxide flux was measured both in root-intact ( R s) and trenched plots ( R mw). The root respiration rate ( R r) was calculated as the difference between R s and R mw. Considering the root distribution in the soil, we regarded the CO2 production rate in the mineral soil to be the microbial respiration rate in the mineral soil ( R mm) and microbial respiration rate in the O-layer ( R mo) as the difference between R mw and R mm. Irrigation increased both soil temperature and moisture in the irrigated plot. The R s, CH4 flux and N2O flux during the irrigation period were higher in the irrigated plot than that in the non-irrigated plot ( P < 0.05; mean R s ± standard deviation [SD] (mg C m−2 h−1) were 171 ± 20 and 109 ± 11, mean CH4 flux ± SD (μg C m−2 h−1) were −5.4 ± 4.1 and −14.0 ± 6.5, and mean N2O flux ± SD (μg N m−2 h−1) were 1.6 ± 1.6 and 0.2 ± 1.1, respectively). Soil moisture had a positive effect on R mm and CH4 production rate in the O-layer, a negative effect on R r, and did not affect R mo, the CH4 production rate in the mineral soil or the N2O production rates in both the O-layer and the mineral soil. Soil temperature had a positive effect on R r and R mo. The increment of global warming potential of the soil mainly resulted from an increase in microbial respiration rates. Future changes in precipitation patterns in this region would accelerate decomposition of the soil organic matter. [ABSTRACT FROM AUTHOR]