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 CO(2) 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 CO(2) loss from streams necessarily underestimate the CO(2) loss with results from two catchments. Dissolved carbon export from headwater catchments is similar to CO(2) loss from stream surfaces. Most of the CO(2) originating in high CO(2) 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 CO(2) uptake. In the Krycklan catchment in Sweden, this more than doubles the CO(2) loss from the catchment. Thus, even when corrected for aquatic CO(2) loss measured by conventional methods, boreal and sub-boreal forest carbon budgets currently overestimate carbon sequestration on the landscape.