CO 2 and CH 4 exchanges between moist moss tundra and atmosphere on Kapp Linné, Svalbard

<p>We measured CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> fluxes using chambers and eddy covariance (only CO<span class="inline-formula">₂</span>) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (9 June–31 August) was negative (sink), with <span class="inline-formula">−</span>0.139 <span class="inline-formula">±</span> 0.032 <span class="inline-formula">µ</span>mol m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span> corresponding to <span class="inline-formula">−</span>11.8 g C m<span class="inline-formula">⁻²</span> for the whole summer. The cumulated NEE over the whole growing season (day no. 160 to 284) was <span class="inline-formula">−</span>2.5 g C m<span class="inline-formula">⁻²</span>. The CH<span class="inline-formula">₄</span> flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511 <span class="inline-formula">±</span> 0.000315 <span class="inline-formula">µ</span>mol m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span>, which corresponds to a growing season estimate of 0.04 to 0.16 g CH<span class="inline-formula">₄</span> m<span class="inline-formula">⁻²</span>. Thus, we find that this moss tundra ecosystem is closely in balance with the atmosphere during the growing season when regarding exchanges of CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span>. The sink of CO<span class="inline-formula">₂</span> and the source of CH<span class="inline-formula">₄</span> are small in comparison with other tundra ecosystems in the high Arctic.</p> <p>Air temperature, soil moisture and the greenness index contributed significantly to explaining the variation in ecosystem respiration (<span class="inline-formula"><i>R</i>_eco</span>), while active layer depth, soil moisture and the greenness index were the variables that best explained CH<span class="inline-formula">₄</span> emissions. An estimate of temperature sensitivity of <span class="inline-formula"><i>R</i>_eco</span> and gross primary productivity (GPP) showed that the sensitivity is slightly higher for GPP than for <span class="inline-formula"><i>R</i>_eco</span> in the interval 0–4.5 <span class="inline-formula">^∘</span>C; thereafter, the difference is small up to about 6 <span class="inline-formula">^∘</span>C and then begins to rise rapidly for <span class="inline-formula"><i>R</i>_eco</span>. The consequence of this, for a small increase in air temperature of 1<span class="inline-formula">^∘</span> (all other variables assumed unchanged), was that the respiration increased more than photosynthesis turning the small sink into a small source (4.5 g C m<span class="inline-formula">⁻²</span>) 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.</p>

Abstract licence: CC BY

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