Riverine carbon flux within the Central Siberian Plateau: terrestrial and climatic controls

Anatoly Prokushkin1, Irina Tokareva1, Mikhail Korets1, Sergey Titov1, Marina Prokushkina2, Alexey Rubtsov2, Oleg Pokrovsky3
1 Lab BGC, VN Sukachev Institute of Forest SB RAS
2 SibFU, Svobodny av. 79, 660041 Krasnoyarsk, Russian Federation
3 GET-CNRS UMR 5563, University of Toulouse, 14 Avenue Edouard Belin, 31400 Toulouse

P 7.19 in Controls of dissolved organic matter fluxes in ecosystems

Permafrost exerts strong controls on the hydrogeochemistry of subarctic rivers by constraining water flow to surface organic-rich soil layers with low residence times and little water-rock interaction. Longer flow paths generally decrease dissolved organic C (DOC) flux to rivers and increase the concentrations of inorganic C (DIC) and other major ions with enhancement of soil organic matter mineralization and bedrock weathering at higher temperatures. Other mechanisms, however, may result in an increase in fluvial export of DOC from Siberian rivers under a changing climate.

Uncertainty in the impacts of climate change on riverine C release from permafrost regions is further complicated by differences in geomorphology, permafrost regime, soil types and vegetation among and within the great rivers that drains to the Arctic Ocean. This uncertainty is particularly large for Yenisey River, which tributaries demonstrate high diversity in watershed properties. The major objective of presented research was to trace terrestrial and climatic controls over the carbon fluxes in rivers of Yenisey River basin. The time series of measurements covers the period from 2005 to 2013 and extended in the past till 1950’s (Roshydromet data).

The study region encompasses >500,000 km2 or roughly one third of the Central Siberian Plateau. Permafrost extends throughout the studied area but ranges from continuous permafrost on the north to isolated patches in the southern parts. The mean annual air temperatures range among basins from -10.9 to -6.3°C.

Riverine C concentrations analyzed over several hydrological years yield typical portrait for subarctic rivers: dominance of the spring freshet in annual cycle, organic form over inorganic, dissolved over particulate. The highest concentrations and aromaticity of DOC occur in spring when runoff originates primarily from organic-rich surface soil layers, intermediate values are found from mineral soil in summer-autumn, and the lowest appear in winter lowflow originating from deep ground water aquifers. Specific fingerprints like dissolved lignin characterized dominant vegetation (Gymnosperm) and its diagenetic alteration separated an input of soil layers in annual flux. As ca. 1% of the territory dominated by larch is affected annually by wildfire, pyrogenic carbon represented another important marker providing insights into the fire disturbance of river basins. In geographical context, there are two contemporary limitations for river export of terrigenous C across studied area: (1) low productivity of ecosystems with respect to potentially mobilizable organic C, slow weathering rates with concomitant small formation of bicarbonate, and/or wildfire disturbance limit the pools of organic and inorganic C that can be mobilized for transport in rivers (source-limited), and (2) mobilization of available pools of C is constrained by low precipitation in the severe continental climate of interior Siberia (transport-limited).

Letzte Änderung 26.06.2014