CO2 and CH4 exchanges between moist moss tundra and atmosphere on Kapp Linne, Svalbard

We measured CO₂ and CH₄ fluxes using chambers and eddy covariance (only CO₂) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (9 June-31 August) was negative (sink) with -0.139±0.032 µmol m^-2s^-1 corresponding to -11.8 g C m^-2 for the whole summer. The cumulated NEE over the whole growing season (day no. 160 to 284) was -2.5 g C m^-2. The CH₄ flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511±0.000315 µmol m^-2s^-1 which corresponds to a growing season estimate of 0.04 to 0.16 g CH₄ m^-2. Thus, we find that this moss tundra ecosystem is closely in balance with the atmosphere during growing season when regarding exchanges of  CO₂ and CH₄. The sink of CO₂ as well as the source of CH₄ are small in comparison with other tundra ecosystems in high Arctic.

Air temperature, soil moisture and greenness index contributed significantly to explain the variation in ecosystem respiration (R_eco) while active layer depth, soil moisture and greenness index were the variables that best explained CH₄ emissions. Estimate of temperature sensitivity of R_eco and gross primary productivity (GPP) showed that the sensitivity is slightly higher for GPP than for R_eco in the interval 0 – 4.5 ºC, thereafter the difference is small up to about 6 ºC and then it began to raise rapidly for R_eco. The consequence of this, for a small increase in air temperature of 1 degree (all other variables assumed unchanged) was that the respiration increased more than photosynthesis turning the small sink into a small source (4.5 gC m^-2) during the growing season. Thus, we cannot rule out that the reason why the moss tundra is close to balance today is an effect of the warming that has already taken place in Svalbard.