Traits of peat- and upland-derived stream dissolved organic carbon in the permafrost region around Abisko, northern Sweden

Abstract: Climate change-induced thawing of permafrost mobilizes previously frozen carbon of high potential reactivity, thereby, fuelling microbiological production of greenhouse gases. For this work, an analysis of the quantity, quality, and bioreactivity of DOC in streams from the Stordalen discontinuous permafrost catchment was carried out with stream water samples during the relatively warm summer of 2018. In the study area permafrost is limited to peatland which is present in lowland areas. We hypothesized that (i) peatland-influenced streams have a higher dissolved organic carbon (DOC) concentration than streams in upland areas of the Stordalen catchment. However, no strong differences in the quantity of DOC between peaty lowland and well-drained upland areas were found. In general, DOC quantity was lower compared to levels obtained by previous studies conducted in the area but due to the lack of discharge measurements for this study, a comparison with other studies is difficult. Furthermore, no clear pattern was detected regarding the extent of carbon degradation, represented by a small range of the ratio between the isotopically stable carbon-12 and carbon-13. However, a slightly enhanced degradation in areas located in upland areas was detected. Additionally, it was predicted that (ii) DOC from upland areas was associated with low molecular weight and relatively high bioreactivity compared to DOC derived from peaty lowland areas. The DOC from all sampled sub-catchments, including the lowland sampling points in the peat, showed surprisingly high bioreactivity, although the upland catchments, where peat was not present, were generally associated with the lowest molecular weights and highest bioreactivity of the DOC. Upland areas are characterised by a faster turnover of carbon, as oxygen can diffuse into the shallow organic layer. Thus, (iii) the share of labile C was higher in better-drained upland areas than in peatland areas. This work showed how quantifiable amounts of low molecular weight DOC can reach streams from permafrost catchments during a warm and dry summer, due to the increasing thickness of the active layer.