Abstract

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 (June–August) was −0.40 g C m−2 day−1 or −37 g C m−2 for the whole summer. Including spring and autumn periods the NEE was reduced to −6.8 g C m−2 and the annual NEE became positive, 24.7 gC m−2 due to the losses during the winter. 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. We find that this moss tundra emits about 94–100 g CO2-equivalents m−2 yr−1 of which CH4 is responsible for 3.5–9.3 % using GWP100 of 27.9 respectively GWP20. Air temperature, soil moisture and greenness index contributed significantly to explain the variation in ecosystem respiration (Reco) while active layer depth, soil moisture and greenness index were the variables that best explained CH4 emissions. Estimate of temperature sensitivity of Reco and gross primary productivity showed that a modest increase in air temperature of 1 degree did not significantly change the NEE during the growing season but that the annual NEE would be even more positive adding another 8.5 g C m−2 to the atmosphere. We tentatively suggest that the warming of the Arctic that has already taken place is partly responsible for the fact that the moist moss tundra now is a source of CO2 to the atmosphere.

Highlights

  • Climate warming is predicted to be most evident at high latitudes (Friedlingstein et al, 2006)with profound effects on ecosystem functioning

  • We quantify ecosystem respiration (Reco), gross primary productivity (GPP) and net ecosystem exchange (NEE) during the growing season based on measurements and we extend the time period to a full year by modelling

  • For CO2 exchanges and partitioning we combined the soil efflux measurements with the chamber system with the eddy covariance flux measurements. This was crucial for the partitioning and for gap filling because from 20 April to 20 August at this location the sun is above the horizon 24 hours of the day and this means that there were few occasions of dark nighttime measurements with the eddy covariance system and all of these were collected at the very end of the summer

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Summary

Introduction

Climate warming is predicted to be most evident at high latitudes (Friedlingstein et al, 2006)with profound effects on ecosystem functioning. One of the high latitude regions that are expected to experience the most dramatic changes caused by climate change is the Arctic. This region which is located roughly north of the tree-line is characterized by cold winters and cool summers and with mean annual temperatures below zero. Soil moisture and greenness index contributed significantly to explain the variation in ecosystem respiration (Reco) while active layer depth, soil moisture and greenness index were the variables that best explained CH4 emissions. Estimate of temperature sensitivity of Reco and gross primary productivity showed that a modest increase in air temperature of 1 degree did not significantly change the NEE during the growing season but that the annual NEE would be even more positive adding another 8.5 g C m-2 to the atmosphere. We tentatively suggest that the warming of the Arctic that has already taken place is partly responsible for the fact that the moist moss tundra now is a source of CO2 to the atmosphere

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