Abstract
Global warming can substantially affect the export of dissolved organic carbon (DOC) from peat-permafrost to aquatic systems. The direct degradability of such peat-derived DOC, however, is poorly constrained because previous permafrost thaw studies have mainly addressed mineral soil catchments or DOC pools that have already been processed in surface waters. We incubated peat cores from a palsa mire to compare an active layer and an experimentally thawed permafrost layer with regard to DOC composition and degradation potentials of pore water DOC. Our results show that DOC from the thawed permafrost layer had high initial degradation potentials compared with DOC from the active layer. In fact, the DOC that showed the highest bio- and photo-degradability, respectively, originated in the thawed permafrost layer. Our study sheds new light on the DOC composition of peat-permafrost directly upon thaw and suggests that past estimates of carbon-dioxide emissions from thawed peat permafrost may be biased as they have overlooked the initial mineralization potential of the exported DOC.
Highlights
The above studies indicate that a substantial fraction of permafrost soil dissolved organic carbon (DOC) may be either photo- or bio-degradable
We compared the optical characteristics of DOC originating from the active layer and the thawed permafrost layer to evaluate the potential effect of permafrost thaw on the DOC properties in receiving ecosystems
The concurrent analysis of the various facets of DOC composition and degradability showed that the initial degradability of this DOC fraction was higher in the thawed permafrost layer than in the active layer, suggesting an efficient loss on its way to the receiving aquatic ecosystems
Summary
The above studies indicate that a substantial fraction of permafrost soil DOC may be either photo- or bio-degradable. Most studies have assessed bio- and photo-reactivity separately or they have been conducted in mineral soil and not organic (peat) permafrost. No study has concurrently measured and compared the bio- and photo-degradability of peat-permafrost DOC with DOC from the active layer. The aim of this study was to simultaneously compare the bio- and photo-reactivity of the DOC extracted directly from experimentally thawed peat-permafrost with DOC derived from the overlaying active layer. We further incubated the soil pore water extracts to assess the bio- and photo-degradation of DOC, and the metabolic response of the natural bacterial assemblage
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