Current forest carbon fixation fuels stream CO₂ emissions

Area of Science:

• Ecology
• Biogeochemistry
• Environmental Science

Background:

• Stream carbon dioxide (CO2) emissions significantly impact climate forcing.
• Groundwater inputs are suspected to sustain stream CO2 emissions, but pathways remain unclear.

Purpose of the Study:

• To investigate the biogeochemical pathways and timescales of lateral CO2 export from streams.
• To determine the source and age of CO2 emitted from streams in a boreal forest ecosystem.

Main Methods:

• Extensive radiocarbon (14C) characterization of CO2 and dissolved organic carbon (DOC) in stream water.
• Analysis of CO2 and DOC from groundwater sources within an old-growth boreal forest.

Main Results:

• Stream CO2 showed radiocarbon levels consistent with contemporary atmospheric CO2.
• Stream CO2 14C levels were largely independent of the 14C-DOC in the same water samples.
• Indicates a direct, rapid pathway for CO2 return to the atmosphere.

Conclusions:

• Stream CO2 emissions act as a 'shortcut' for recently photosynthesized carbon from forest vegetation to the atmosphere.
• This represents a positive feedback in forest catchment carbon budgets.
• Stream CO2 emissions are highly sensitive to forest carbon allocation shifts driven by climate and land-use changes.