The effect of open-water pools on the net ecosystem CO2 exchange of a boreal peatland

Peatland open-water pools are a common feature on temperate, boreal and subarctic peatlands. A limited number of studies, focusing mainly on the growing season, have shown pools to represent net sources of carbon dioxide (CO₂) to the atmosphere. However, their impact on the net ecosystem carbon dioxide (NEE-CO₂) is poorly understood. Considering the magnitude of the CO₂ flux from these water bodies, it is uncertain whether peatlands with open water pools are net sink for CO₂. To date, the evaluation of the CO₂ budget of peatlands with pools has only been explored through spatial extrapolation and temporal interpolation of point measurements made using static chambers; the errors introduced by such method can be larger than the fluxes. In this study, we measured the annual CO₂ exchange from peatland open-water pools, we assessed if the presence of pools has a measurable impact on the peatland NEE-CO₂, and we evaluated the CO₂ sink potential. We measured open water CO₂ flux using a combination of the headspace technique and a non-dispersive infrared CO₂ sensor. NEE-CO₂ was measured using eddy covariance. Our results confirm that the peatland open-water pools are a significant source of C to the atmosphere, with an annual release of 103 g C m^-2, of which 15% was released during the ice-met period. The CO₂ release from the pools had a measureable impact on the NEE-CO₂; an increase in pool contribution to the ecosystem CO₂ fluxes results in a reduction in both ecosystem level maximum gross photosynthesis and ecosystem respiration. Despite significant CO₂ loss from the pools, we found the overall peatland to be a net sink for CO₂ for the measurement period.