Comprehensive multiyear carbon budget of a temperate headwater stream

Headwater streams comprise nearly 90% of the total length of perennial channels in global catchments. They mineralize organic carbon entering from terrestrial systems, evade terrestrial carbon dioxide (CO 2 ), and generate and remove carbon through in‐stream primary production and respiration. Despite their importance, headwater streams are often neglected in global carbon budgets primarily because of a lack of available data. We measured these processes, in detail, over a 10 year period in a stream draining a 96 ha forested watershed in western Oregon, USA. This stream, which represents only 0.4% of the watershed area, exported 159 kg C ha −1 yr −1 , similar to the global exports for large rivers. Stream export was dominated by downstream transport of dissolved inorganic carbon (63 kg C ha −1 yr −1 ) and by evasion of CO 2 to the atmosphere (42 kg C ha −1 yr −1 ), leaving the remainder of 51 kg C ha −1 yr −1 for downstream transport of organic carbon (17 kg C ha −1 yr −1 and 34 kg C ha −1 yr −1 in dissolved and particulate form, respectively).