This presentation describes the methods and case studies of element flux measurements in the Arctic and subarctic rivers, in the Russian boreal and subarctic zone, along the gradient of permafrost-free terrain to continuous permafrost settings, developed on various lithology and vegetation coverage. The majority of existing flux measurements are based on combination of daily discharges from Russian Hydrological Survey gauging stations with punctual or year-around sampling of dissolved and particulate load following the chemical analysis. In this chapter, a new, geochemical-based look on the functioning of aquatic boreal systems is described which takes into account the role of the following factors on riverine element fluxes: 1) the specificity of lithological substrate; 2) the importance of organic and organo-mineral colloidal forms, notably during the spring flood; 3) the role of permafrost presence within the small and large watersheds and 4) the governing role of terrestrial vegetation in element mobilization from rock substrate to the rivers. Care of such a multiple approach, a first order prediction of element fluxes under scenario of progressive warming in high latitudes becomes possible. Two novel dimensions added to the existing knowledge of element transport from the land to the Arctic Ocean by the Russian boreal and subarctic rivers are i) evaluation of colloidal flux of dissolved substances and low molecular weight fraction and ii) assessing for the first time, the isotopic signatures of Ca, Mg, Si and Fe in several case watersheds of various lithology and permafrost coverage.
Results of this study and available literature data demonstrate that, while the climate warming will certainly affect the winter-time element fluxes and speciation, it is unlikely to change the nature and magnitude of the main fraction of TE flux to the ocean. This fraction of the flux occurs in colloidal form during several weeks of the springflood. At the present time it is not strongly affected by the climate change, or this influence is within the uncertainty of flux measurements. Overall, the major changes in the chemical and isotopic nature of riverine fluxes to the Arctic Ocean from Northern Eurasia under climate warming scenario are likely to be linked to the change of vegetation (species, biomass and geographical extension), rather than temperate and hydrology. The increase of the depth of active layer has an influence of the secondary order importance on the riverine fluxes given that the majority of continental flux to the Arctic Ocean is formed on permafrost soils, highly homogeneous over the depth profile.