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Winter Blog: Cherskii 2013 ´´Flux measurement in winter´´

Chamber measurement in winter time (with evolving sledge) Chamber measurement in winter time (with evolving sledge)  Tuesday, 3rd of December 2013
 
When we were planning to come to Cherskii for fall/winter flux measurements, many people asked us if the permafrost ecosystem would be active in the fall/winter, i.e. whether or not any gas emits from soil at below zero degrees.
 
The short answer is yes, and surprisingly even photosynthesis (CO2 consumption) occurs by some lichen species, even though it was neither observed at very cold temperatures like -30 degrees nor with a thick snow layer on the ground – sunlight will hardly pass through thick layer of snow pack.

Basically the environment observational setup to capture the fluxes is similar at any season, but one big difference that needs to be considered for the measurement strategy in winter season obviously is the presence of snow. To measure flux with chambers, some people remove snow from the ground and measure directly on the ground, while others put chambers on top of snow.
 
Hotspots for gas emission through “tussock shadow”Hotspots for gas emission through “tussock shadow”There are several other indirect methods but these two are widely used. The reason why some people remove snow is that snow can absorb/preserve gases and the flux measured on top of the snow might not represent "real time" flux emitted by the ecosystem (usually the signal is underestimated and delayed). Despite of this, we decided not to remove snow.
 
The main reason is to not destroy the chamber sites. We have specific chamber locations where some sensors/probes are permanently installed, which we plan to use long-term over the coming years. So if we remove snow, the soil temperature would be different from that of the surrounding environment that is still covered by snow since the snow is very important for insulation.
 
As a consequence, if wintertime soil temperature changes (drops) because of snow removal, the flux measurements including those within the following seasons, will be affected by different soil processes. Primarily flux (emission rate) can be lower than it should be because of lower temperature. Physical processes can also change the flux pattern – depending on how rapidly it freezes soil or how much the temperature fluctuates over time without insulation. Moreover, one of the objectives of our study is to compare/upscale the chamber data to eddy covariance data, so if we disturb the chamber sites, their representatives for comparing with the eddy data will be poor.
 
(Photo 1) One very interesting pattern we observed in our data sets so far is the occurrence of higher flux rates in some chamber sites where big tussocks prevent accumulation of a closed snow cover on the ground. These exposed tussock sites appear to be very important pathways for gas exchange with the atmosphere so we are excited to see this variation depending on snow cover among chamber sites. (Photo 2)

One good thing is that the snow depth is not very high in our site so this shallow snow layer is not influencing flux so much. Snow is also changing like sand in desert ecosystems sometimes. Snow was accumulating gradually every day when it snowed and it stayed almost the same for the next days. But one time strong wind blew and the next day all the tracks of sledge and marks of chambers were disappeared. This can also compensate our disturbance while visiting chambers.
 
Written by Min
 
 
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