Sergey N. Vorobyev

Thermokarst lakes of Western Siberia: a complex biogeochemical multidisciplinary approach

Western Siberia’s thermokarst lakes are highly dynamic hydrochemical systems that receive chemical elements from the surrounding peat soil and exchange greenhouse gases with the atmosphere, delivering dissolved carbon and metals to adjacent hydrological systems. Climate warming is likely to intensify the magnitude of these processes, thus seriously affecting the biogeochemical fluxes both on land and in the coastal zone of the Arctic Ocean. In this work, we review biogeochemical and morphological features of thermokarst water bodies comprising frozen palsa depressions up to large, kilometre-size lakes and drained lakes. Based on a compilation of more than a hundred analyses of these water bodies, we discuss the average concentration of organic carbon, as well as the major and trace elements, and predict the development of their chemical composition, CO2 and CH4 exchange with the atmosphere and effect on the riverine fluxes from the land to the ocean under the climate-warming scenario. The accelerating permafrost thaw and rising water temperatures in this region will probably shorten the life cycle of the thermokarst thaw water bodies, increase the fluxes of both CO2 and CH4 into the atmosphere, increase the concentration and delivery of dissolved organic carbon and related trace metals to the hydrological network and increase the potential bioavailability of micronutrients. Thus, the impact of permafrost thaw in Western Siberia on the global plantery processes, via the retroactive link between climate change and the thermokarst lakes’ geochemical activity, may be more significant than is currently expected.

The role of Eurasian beaver (Castor fiber) in the storage, emission and deposition of carbon in lakes and rivers of the River Ob flood plain, western Siberia

Several studies have reported significant emission of greenhouse gasses (GHG) from beaver dams, suggesting that ponds created by beavers are a net source of CO2 and CH4. However, most evidence come from studies conducted in North America (on Castor canadensis) without a parallel comparison with the Eurasian beavers (Castor fiber) impacts and a critical consideration of the importance of the carbon deposition in dam sediments. The most abundant population of the Eurasian beaver lives in Russia, notably within the River Ob watershed in Western Siberia which is the second largest floodplain on Earth. Consequently, we assessed the holistic impact of Eurasian beavers on the multiple carbon pools in water and on other related biogeochemical parameters of the Obs floodplain streams. We compared dammed and flowing streams in a floodplain of the middle course of the river. We found that beavers in western Siberia increase the stream emission of methane by about 15 times by building their dams. This is similar to what has been documented in North America. A new finding from the present study is that Siberian beavers facilitate 1) nutrient recycling by speeding up the nutrient release from particulate organic matter; and 2) carbon sequestration by increasing the amount of dissolved organic carbon. This carbon becomes in part recalcitrant when buried in sediments and is, therefore, removed from the short-term carbon cycle. These new results should be taken into consideration in river management and provide a further reason for the conservation and management of Eurasian Beavers.