Fig 3. Significant relationship between permafrost soil area as a percentage of watershed area (%) and ¹⁴C age of dissolved organic carbon (DOC) in years before present.

Note: samples 3 and 15 were not included in the regression because the old DOC ages of these two samples were attributed to factors other than permafrost carbon contributions. Sample 3 was collected from the lower reaches of the large Longyangxia reservoir on the main stem of the Yellow river. The long residence time of water in the reservoir [23] or carbon age reservoir effects [50] may therefore have contributed to the old ¹⁴C age of DOC in this sample. Sample 15 was collected from Yarlung Tsangpo Grand Canyon, the region with the maximum topographic slope on the Tibetan Plateau [51].