Tundra regions of the world are characterized by a large amount of carbon stored in soils that could be released in the atmosphere with change in hydrology and temperature due to climate change. In the Arctic, recent evidence indicate that some Arctic areas on continuous permafrost are showing an increased number and extent of lakes. Therefore, even under scenarios of warming and drying of the Arctic, many regions underlain by continuous permafrost are likely to show increased water availability in coming decades. This means an increase in the water table over extensive tundra regions, which could result in large new areas of anaerobic soils, affecting respiration rates and carbon release/uptake to the atmosphere.

Several studies indicated that a decrease in the water table in the arctic tundra increases the CO₂ release into the atmosphere. However, to our knowledge, the effect of rise in water table above the surface level on the Net Ecosystem Exchange of large section of arctic tundra has never been investigated before.

In our experiment, through the use of three permanent eddy covariance towers, we measured CO₂ fluxes over three adjacent large areas (ha scale), where we manipulated water table levels.

Results/Conclusions

Here we show that the increase in the water table has a major effect on the CO₂ fluxes in the Arctic tundra, switching the ecosystem from a summer carbon sink to a slight carbon source. This is probably the result of light limitation of photosynthesis, as vegetation, covered by water, has lower light availability.

The results of this research highlights another unexpected aspect of the vulnerability of the arctic ecosystems to the change in climate and the consequences that possible or observed changes in hydrology have on the productivity of tundra regions. This is particularly relevant as it has been shown that in areas underlain by continuous permafrost the total lake area increased by 13,300 ha. This means an increase in water table over extensive tundra regions.

Even though study has been carried in Alaska and the observed lake extent change has been observed in Siberia, these two areas have similar vegetation, so the implication of this study are of major relevance for the whole arctic carbon balance.

Moreover, even if the Arctic Alaskan tundra has not shown an increase in lake extent in the continuous permafrost regions that has been observed in Siberia , therefore there is the risk of observing such change also in the Alaskan Arctic.