Pan‐Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land‐to‐ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high‐latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high‐latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan‐Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr−1 and 216 Gg yr−1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high‐latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean.

The colloidal distribution and size fractionation of organic carbon and trace elements were studied in a seasonally stratified, organic-rich boreal lake, Lake Maselga, located in the European subarctic zone (NW Russia, Arkhangelsk region). This study took place over the course of 5 years in winter (glacial) and summer periods and during the spring and autumn overturn. A newly developed in situ dialysis technique (1, 10, and 50 kDa) and traditional frontal filtration and ultrafiltration (20, 10, 5, 0.22, and 0.025 lm) were used to assess element concentrations at different depths. No significant changes in element concentrations occurred during filtration through sub-colloidal pore-size membranes (20-0.22 lm), suggesting a negligible amount of particulate Fe, OC, and associated trace metals. Large colloids (0.025-0.22 lm) were found to be the main carriers of poorly soluble elements (Fe, Al, Ti, Zr, REEs, Th, and U) during the summer and winter stratification. There was also a clear change in the vertical pattern of the percentage of colloidal Al, Ti, V, Cr, Fe, and Ni during different seasons, and the greatest proportion of colloidal forms was observed during the spring and autumn overturn. This pattern is most likely linked to the dominance of soil (allochthonous) organic carbon, which complexes with trace metals during these periods. During the summer seasons, autochthonous production of small exometabolites or photodegradation increases the concentration of the lowmolecular weight fractions (\1 kDa) that dominate the speciation of divalent heavy metals Electronic supplementary material The online version of this article (in surface horizons. The colloidal status of As (30-60%), which was documented in different seasons along the full depth of the water column, is most likely linked to the presence of organic complexes. The overall results of this study suggest that changes in the colloidal speciation of trace elements with depth in different seasons depend on changes in the redox conditions, the input of soil OM, the biodegradation of plankton biomass releasing dissolved organic matter in the bottom horizons, and in upward diffusion from the sediments.

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Acid ionization constants of the phenolic hydroxy groups of guaiacol derivatives in water3acetone mixtures were determined. The acidity of these phenols was analyzed in relation to both the acetone content in the mixed solvent and kind of para-substituent.Neat acetone and water3acetone mixtures are promising solvents for cooking of wood and modification of commercial lignin [133]. However, the solvent effect on the protolytic properties of phenol-containing structural units of lignin, mainly governing their reactivity, is poorly understood. In order to characterize the lignin reactivity, data on the acidity of its separate structural fragments in aqueous and aqueous3 organic media are required [4].In this work we studied the acidity of phenolic hydroxy groups of a series of guaiacol derivatives in water3acetone mixtures. The most reliable data on protolytic equilibria in solutions can be obtained by potentiometric titration with a glass electrode and by UV spectrophotometry [1,3, 537]. However, the spectrophotometric determination of pK a of phenols in water3acetone mixtures is impossible since the absorption bands of phenols and acetone (<300 nm) overlap [8]. Therefore, in this work pK a of phenolic hydroxy groups was determined by potentiometric titration with an aqueous base using a glass electrode [11].In this work we studied the acidity of nine guaiacol derivatives modeling certain structural fragments of coniferous lignin containing substituent R in a-position to the propane chain in the lignin structure:where R = H (guaiacol), CH 3 (creosol), COH (vanillin), COCH 3 (acetovanillone), CH=CHCH (isoeugenol), CH 2 CH=CH 2 (eugenol), CH=CHCOOH (ferulic acid), COOH (vanillic acid), and CH 2 OH (vanillic alcohol).All the guaiacol derivatives were of pure grade (Aldrich). Acetone, chemically pure grade (Ekros), was used without additional purification.In our experiments, the acidity of guaiacol derivatives was studied using their 0.01 M solutions in water3acetone mixtures. 20% aqueous tetraethylammonium hydroxide (Merck) was used as titrant. The potentiometric titration of aqueous-acetone solutions of guaiacol derivatives was carried out under argon with continuous stirring in a temperature-controlled glass cell at 25 + 0.1 oC. pH was measured on an Ekspert-001 (Ekoniks3Ekspert, Moscow) pH-ionometer equipped with an ESL-63-07 glass electrode and an EVL-1-M3 silver chloride electrode. This device was calibrated relative to aqueous reference solutions immediately before measurements. pK a was determined in each point of the titration curve by the equationwhere pH is the measured pH value in each point along the titration curve up to an equivalent point; V e , equivlent volume of titrant; and V, added titrant volume.The averaged experimental pH values of aqueousacetone solutions of guaiacol derivatives were recalculated to the negative logarithm of the proton activity pa H + relative to the proton activity in the infinitely dilute aqueous-acetone solution as standard state. This recalculation was carried out using the...

In the conditions of climate warming, the thawing of permafrost can provoke the formation of new thermokarst lakes and subsidence, which facilitates the removal of organic matter from thawed peat into natural waters. Hydrochemical studies of surface waters of the Bolshezemelskaya tundra have demonstrated the exponential dependence of the physicochemical parameters on the size of the water body (peat subsidence, thaw ponds, small lakes, thermokarst lakes). The hydrochemical features of thermokarst lakes of the Bolshezemelskaya tundra are determined by high content of DOC, surface runoff and the thickness of peat deposits. Measurements of concentrations and fluxes of methane showed that all studied water bodies of the Bolshezemelskaya tundra are oversaturated with CH4, and depressions, subsidence, and small water bodies (<100 m2) are characterized by the highest concentrations of DOCs. The contribution of these small reservoirs to the total coverage of the surface of the Bolshezemelskaya tundra area is significant, and their consideration can greatly change the assessment of methane fluxes from the arctic tundra.