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The hydraulic properties of ground vegetation cover are important for high resolution hydrological modeling of permafrost regions, due to its insulating and draining role. In this study, the morphological and effective hydraulic properties of Western Siberian Lowland ground vegetation samples (lichens, Sphagnum mosses, peat) are numerically assessed based on tomography scans. After numerical pre-processing, porosity is estimated through a void voxels counting algorithm, showing the existence of representative elementary volumes (REV) of porosity for most samples. Then, two methods are used to estimate hydraulic conductivity depending on the sample's homogeneity. For the most homogeneous samples, Direct Numerical Simulations (DNS) of a single-phase flow are performed, leading to a definition of hydraulic conductivity related to REV, which is larger than those obtained for porosity. For more heterogeneous samples, no adequate REV may be defined. To bypass this issue, a pore network representation of the whole sample is created from computerized scans. Morphological and hydraulic properties are then estimated through this simplified representation. Both methods converged on similar results for porosity. Some discrepancies are observed in the morphological properties (specific surface area). Hydraulic conductivity fluctuates by two orders of magnitude, depending on the method used, and yet this uncertainty is less than that found in experimental studies. Therefore, biological and sampling artifacts are predominant over numerical biases. Porosity values are in line with previous values found in the literature, showing that arctic cryptogamic cover can be considered as an open and well-connected porous medium (over 99 % of overall porosity is open porosity). Meanwhile, digitally estimated hydraulic conductivity is higher compared to previously obtained results based on field and laboratory experiments. This could be related to compressibility effects, occurring during field or laboratory measurements. Thus, some supplementary studies are compulsory for assessing syn-sampling and syn-measurement perturbations in experimentally estimated, effective hydraulic properties of such a biological porous medium. [ABSTRACT FROM AUTHOR]

Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-size rivers remain poorly unknown. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94,000 km2) which drains through virtually pristine dense taiga forest of the boreal zone in western Siberian Lowland (WSL). We combined continuous in-situ measurements of carbon dioxide (CO2) concentration and flux (FCO2), with methane (CH4), organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over a 834-km transect of the Ket River main stem and its 26 tributaries during spring flood and 12 tributaries during summer baseflow. The CO2 concentration was lower and less variable in the main stem (2000 to 2500 µatm) compared to that in tributaries (2000 to 5000 µatm). The methane concentrations in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 (baseflow period) lower than that of CO2. The FCO2 ranged from 0.4 to 2.4 g C m-2 d-1 in the main channel and from 0.5 to 5.0 g C m-2 d-1 in the tributaries, being the highest during August in tributaries and weakly dependent on season in the main channel. Only during summer baseflow, the DOM aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO2 concentrations and fluxes. We hypothesize that the relatively low variability in FCO2 is due to flat homogeneous (bog and taiga forest) landscape that results in long water residence times and stable input of allochthonous DOM, which dominate the FCO2. In summer baseflow, the DIC input from deeper flow paths might also contribute to CO2 emission. The open water period (May to October) C emission from the Ket River basin was estimated to 127±11 Gg C y-1 which is lower than the lateral C export during the same period. Although this estimated C emissions contain uncertainties, stressing the need of better constrained FCO2 and water coverage across seasons, we considered it conservative which emphasize the important role of WSL rivers for release of CO2 to the atmosphere. [ABSTRACT FROM AUTHOR]

Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-size rivers remain poorly unknown. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94,000 km²) which drains through virtually pristine dense taiga forest of the boreal zone in western Siberian Lowland (WSL). We combined continuous in-situ measurements of carbon dioxide (CO2) concentration and flux (FCO2), with methane (CH4), organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over a 834-km transect of the Ket River main stem and its 26 tributaries during spring flood and 12 tributaries during summer baseflow. The CO2 concentration was lower and less variable in the main stem (2000 to 2500 µatm) compared to that in tributaries (2000 to 5000 µatm). The methane concentrations in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 (baseflow period) lower than that of CO2. The FCO2 ranged from 0.4 to 2.4 g C m-2 d-1 in the main channel and from 0.5 to 5.0 g C m-2 d-1 in the tributaries, being the highest during August in tributaries and weakly dependent on season in the main channel. Only during summer baseflow, the DOM aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO2 concentrations and fluxes. We hypothesize that the relatively low variability in FCO2 is due to flat homogeneous (bog and taiga forest) landscape that results in long water residence times and stable input of allochthonous DOM, which dominate the FCO2. In summer baseflow, the DIC input from deeper flow paths might also contribute to CO2 emission. The open water period (May to October) C emission from the Ket River basin was estimated to 127±11 Gg C y-1 which is lower than the lateral C export during the same period. Although this estimated C emissions contain uncertainties, stressing the need of better constrained FCO2 and water coverage across seasons, we considered it conservative which emphasize the important role of WSL rivers for release of CO2 to the atmosphere. [ABSTRACT FROM AUTHOR]

Research is presented on dolomite steady-state dissolution rates in a mixed-flow reactor at 25 degrees Celsius. Findings for ionic strength, pH function, calcium, magnesium, total dissolved carbonate, and organic and inorganic ligands concentration are discussed.