Large Carbon Dioxide Fluxes from Headwater Boreal and Sub-Boreal Streams

Half of the world''s forest is in boreal and sub-boreal ecozones, containing large carbon stores and fluxes. Carbon lost from headwater streams in these forests is underestimated. We apply a simple stable carbon isotope idea for quantifying the CO₂ loss from these small streams; it is based only on in-stream samples and integrates over a significant distance upstream. We demonstrate that conventional methods of determining CO₂ loss from streams necessarily underestimate the CO₂ loss with results from two catchments. Dissolved carbon export from headwater catchments is similar to CO₂ loss from stream surfaces. Most of the CO₂ originating in high CO₂ groundwaters has been lost before typical in-stream sampling occurs. In the Harp Lake catchment in Canada, headwater streams account for 10% of catchment net CO₂ uptake. In the Krycklan catchment in Sweden, this more than doubles the CO₂ loss from the catchment. Thus, even when corrected for aquatic CO₂ loss measured by conventional methods, boreal and sub-boreal forest carbon budgets currently overestimate carbon sequestration on the landscape.