Land-Atmosphere exchange of CO2, water and energy at a boreal minerotrophic mire

• Main Author: Sagerfors, Jörgen
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2007
• Subjects: Arctic
• Online Access: https://pub.epsilon.slu.se/1320/; https://pub.epsilon.slu.se/1320/1/Thesis_v1.04.pdf

Boreal and sub-arctic peatlands cover a small part of the global land area (only ca 3%) but have stored considerable amounts of carbon during Holocene. The carbon stored is equivalent to ~ 20-30% of the global soil carbon pool and ~ 40-60% of the carbon currently held in the atmosphere as CO2. Due to the enormous amounts of carbon available in the peat, great interest has been paid to whether the carbon will remain in the peatlands, or migrate to the atmosphere. The current fluxes of carbon between these ecosystems and the atmosphere are therefore considered to be important in global carbon budgets, and may be even more important in the future, if the exchange rates change in response to anticipated climatic changes. Five years of continuous Eddy Covariance measurements on an acid, oligotrophic, minerogenic, mixed mire, Degerö Stormyr, has shown that the mire ecosystem was a stable sink for CO2, with an uptake of 54 ± 6 gCO2-Cm-2y-1 (±SD). Also when considering carbon effluxes such as by CH4-C or carbon in the runoff water, the mire still remains as a stable sink of 27 ± 6 gCm-2yr-1 (±SD). A positive water balance is a prerequisite for the development and maintenance of peatland ecosystems. The water balance is, in turn, intimately connected to the energy balance at any site since the partitioning into evapotranspiration of water directly affects the water balance. The water balance is delicately controlled by the relationship between precipitation and recharge, evapotranspiration and discharge. A high water table is required to maintain the moist environment essential for mire plant species. Both the annual water balance and the within-year variability in water balance affect the development and maintenance of mires. By combining traditional measurements of precipitation and runoff with Eddy Covariance measurements of evapotranspiration, we could achieve an estimate of the total water balance and further analyze seasonal variations in the respective water pathways. The mire did not show any sign of water limitation within a wide range of water levels measured during the five years of the study. Mire systems are often considered to be “wet” and are sometimes compared to lakes. Data from Degerö Stormyr shows that the opposite is more common, that the mire is house-holding with its water and that a mire surface with low water content has relatively lower evapotranspiration than many other ecosystems such as e.g. a forest ecosystem. Therefore we conclude that regarding the water availability at Degerö Stormyr, it is at a stable equilibrium and extreme changes are needed to alter the present water regime and in turn, alter the carbon balance into a source.