Soil-atmosphere gas exchange of CO2

Technical information

Automated closed static automatic chambers ("Toheli") are used for continuous soil CO₂ efflux measurements. The chambers are planned and constructed by Topi Pohja. They are made of transparent PMMA (acryl). Thickness of the sides and UV-permeable cover is 6 mm and 3mm, respectively. The chamber is 250 mm in height of which 70 mm is aluminum collar.  The ground area of the chamber sides is 250 mm times 200 mm and it is open towards the ground. Seal is rubber (sienikumi).

Operation of each chamber is controlled with microcontroller box (by Heikki Laakso). The chamber opens and closes by a gear motor (hammasvaihdemoottori)* with circa 4 rounds per minutes or by compressed air (2009->). In 2009, the chamber has been programmed to be closed for 3½ minutes every 30 minutes. Earlier, the chamber was mostly closed for the 3½ minutes but stayed opened thereafter for 30 minutes. The controller gives sign whether the chamber is closed or open. The state is found from the data file.

The system uses 12 VDC. The need for currency is circa 300 mA in motion and 20 mA immobilized.

In the chambers, there is a fan with a diameter of 25 mm and air temperature measurements. Vaisala CARBOCAP® Carbon Dioxide Probe GMP343 (Vaisala Oyj, Vantaa,Finland) enters the chamber through a hole on one of the sides. The measurement signal is automatically corrected for temperature but the oxygen, pressure and moisture corrections are turned off. (Pressure affects the oxygen correction.) Therefore, the concentrations must be corrected afterwards according to Vaisala classified equations. The probes has been calibrated circa once a month. In 2008 there were some technical difficulties and all of the sensors were sent to maintenance during which all the versions were updated from v4 to v7. New versions have been in use from the beginning of 2009. Notice, that there is a slightly different correction equations for the different versions

There is a varying set of other measurements too depending on year and chamber. Usually they are having an air moisture measurements (xx) and radiation sensors (Li-Cor 190SZ and Photodiodes xxx). The exact set of measurements can be concluded from the diaries (.txt, ELOG) and dutyinfo\fileinfo.xls (sheets ToHeLi_1-2 and ToHeLi_3). 

Locations and additional information

In 2008, the chambers were fully darkened with aluminium cover. In 2007 and 2009 they have been transparent except for the time of manual CO2 measurements every second week when the chambers were darkened for couple of hours. The manual measurements are located in the folder \Soil_dynamics\Flx_chambers\CO2_flux.

In 2007 and 2008, there were two chambers. One of them (1; *.vsl, *.vch, *.lis, *.li1) was located on the top of the water catchment near the pit 100 and the valoharava -pole. The other one (3; *.v2k, *.li3) was located near the dam of the big catchment near the pit 80 and next to the soil CO2 profile measurements. There has been only mosses and spare population of linnaea in the chamber1. In the chamber3, there has been a dense population of lingonberry and some blueberry accompanied by Polytrichum.

In 2009, there were three chamber. The additional one (2) was located near pit 100. The data exists in the same file with the chamber 1 (*.li1). Wavy hair grass dominated the vegetation in the chamber.

The total height of the chambers 1/2/3 were 0.20 cm + 0.030/  /0.020 cm;  0.030/  /0.020 cm and 0.022/0.012/0.024 cm in the summers 2007-2009, respectively.

Nowadays two of the chambers are normally transparent and one is covered with aluminum foil to prevent the light from entering the chamber.

Another soil chambers setup: see Tree gas exchange measurements (Photo), reference:

Pumpanen et al., 2001. An open chamber system for measuring soil surface CO₂ efflux: Analysis of error sources related to chamber system. Journal of Geophysical Research, 106, 7985-7992.

CO₂ efflux is also measured manually every two weeks during the snow-free period from 14 collars attached permanently on the soil. The chamber is based on similar measurement principle as the automated chamber, but the shape is different. The chamber has a cylinder shape with 20 cm diameter and height. And the chamber is covered with aluminum foil to prevent the light from entering the chamber.  Air is mixed inside the chamber with a small fan.