Quantity and composition of waterborne carbon transport in subarctic catchments containing peatlands and permafros

Both quantity and composition of waterborne transport of dissolved organic carbon (DOC) from peatlands has been hypothesized to be affected by permafrost thaw. Changes in DOC can impact the carbon (C) balance of peatlands directly, but also the carbon balances and metabolism of downstream aquatic environments. In this study I have investigated the DOC export from different peatland types in the Stordalen catchment of northern Sweden (68.20N, 19.03E). The research was performed at various spatial and temporal scales in order to assess the importance of peatland permafrost thaw for both peatland and catchment DOC export. In the Stordalen catchment, peatland permafrost thaw leads to the conversion of palsas (a rain-fed peatland type with a permafrost core) into bogs dominated by Sphagnum mosses or into fens of varying nutrient status depending on their hydrological setting.;The palsas were found to have low DOC export rates, at between 2.5 and 3.5 g C m-2 yr-1, and its composition characterized by several bulk DOC indices was of poor substrate quality for microbial degradation. The DOC export from the bogs was not found to differ in quantity to that of the palsas, but its DOC composition had lower aromaticity and a larger fraction derived from microbial sources. Snowmelt runoff occurred early on the palsa and bog, and mass flux at this time of years was responsible for >70% of the annual DOC export -- causing the palsas and bogs to significantly affect catchment DOC export patterns during early snowmelt runoff, despite covering <4% of the catchments. Partly due to the restricted DOC export, the Stordalen palsa/bog complex was found to be net annual C sinks despite its low ecosystem productivity.;In contrast, the fens were found to export 2 to 4 times as much DOC as the palsas and bogs, with a majority of the DOC export occurring outside the snowmelt runoff period. Several pieces of evidence show that fens not only act as catchment sources of DOC, but through selective degradation they transform DOC that reach the fens from upstream sources, causing the fens to regulate catchment DOC composition and concentrations during summer and fall low runoff periods despite covering only a small fraction of the catchment area.;The impact on peatland DOC export from permafrost thaw is primarily dependent on the hydrological setting after thaw in Stordalen, where a conversion of palsas into fens has the greatest potential for the alteration of catchment DOC export patterns.