Switching predominance of organic versus inorganic carbon exports from an intermediate-size subarctic watershed

Hydrologic exports of dissolved inorganic and organic carbon (DIC and DOC) reflect permafrost conditions in arctic and subarctic river basins. DIC yields, in particular, increase with decreased permafrost extent. We investigated the influence of permafrost extent on DIC and DOC yield in a tributary of the Yukon River, where the upper watershed has continuous permafrost and the lower watershed has discontinuous permafrost. Our results indicate that DIC versus DOC predominance switches with interannual changes in water availability and flow routing in intermediate-size watersheds having mixed permafrost coverage. Large water yield and small concentrations from mountainous headwaters and small water yield and high concentrations from lowlands produced similar upstream and downstream carbon yields. However, DOC export exceeded DIC export during high flow 2011, whereas DIC predominated during low flow 2010. The majority of exported carbon was derived from near-surface organic sources when landscapes were wet or frozen and from mineralized subsurface sources when infiltration increased.