Partitioning of Dissolved Organic Carbon, Major Element and Trace Metal During Laboratory Freezing of Organic Leachates From Permafrost Peatlands

The climate change is likely to modify the freezing-thawing cycles in soils and surface waters of permafrost-affected and subarctic regions. Yet, the change of solution chemical composition during ice formation and evolution of remaining fluids remain very poorly known. Towards better understanding of dissolved (< 0.45 µm) organic carbon, major and trace elements behavior in permafrost peatland environments, here we performed laboratory freezing of peat leachates, from complete freezing to complete thawing in order to quantify the partitioning of solutes between the aqueous solution and the remaining ice. We hypothesized the existence of two main groups of solutes, behaving conservatively or non-conservatively during freezing depending on their incorporation into the ice or ability to coagulate in the form of insoluble minerals or amorphous materials in the fluid phase. An unexpected result of this work was that, despite sizable degree of element concentration in the remaining fluid and possible coagulation of organic, organo-mineral and inorganic compounds, the freezing and subsequent thawing produced the final concentrations of most solutes which were not drastically different from initial concentrations in starting leachates, prior freezing. This demonstrates high stability of dissolved (< 0.45 µm) OC, Fe, Al and some trace metals to repetitive freezing and thawing of surface waters in permafrost peatlands.