Abstract. Mobilization of dissolved organic carbon (DOC) and related trace elements (TE) from the frozen peat to surface waters in the permafrost zone is one the major consequence of on-going permafrost thaw and active layer thickness (ALT) rise in high latitude regions. The interstitial soil solutions are efficient tracers of on-going bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, DIC and 40 major and TE in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease of the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase of the permafrost coverage, decrease in the annual temperature and ALT, the DOC and many major and trace element did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2° N to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from continuous permafrost zone was equal or higher than that in sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, REEs, Zr, Hf, Th) elements exhibited an increasing, not decreasing northward concentration trend. We hypothesize that the effect of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REE, Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat pore-water enrichments in DOC and other solutes. A two-degree northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, SUVA, Ca, Mg, Fe and Sr will not exceed 20 % of their actual values. The projected increase of ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime are unlikely to modify chemical composition of peat pore water fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2.
Dissolved Organic Matter Characteristics and Important Site Factors in a Subtropical Mountain Forest in Central China
