Soil-atmosphere gas exchange of CH4 and N2O
The forest floor CH4 and N2O fluxes are measured with a manual non-steady-state chamber system placed on six permanently installed collars and samples are taken monthly or bi-weekly and the automatic and four of the manual chambers were placed in the catchment areas, whereas two manual chambers are located outside the catchment (Pihlatie et al. 2007, Aaltonen et al., 2010, Korhonen et al., 2013). The collars and chambers are made of stainless steel and the chamber dimensions are 40cm×29cm×15cm (w×d×h). The height of the collar and chamber together vary from 20 to 25 cm, depending on the vegetation. The chamber closure time is 60 min and four samples are taken 2, 20, 40 and 60 min after closure begins. The CH4 and N2O fluxes are estimated from a regression fitted to the four concentration readings.
The automatic chamber was made of stainless-steel (0.40×0.80×0.32m: width×length×height), it is equipped with two fans and a thermocouple for chamber air temperature measurement. The chamber is automatically closing 1-4 times per day for 60 min. During each enclosure a minimum of 4 gas samples are withdrawn from the headspace by a custom made autosampler (MaSa, Pohja-Metallityöpaja, Juupajoki, Finland).
The concentrations of CH4 and N2O in the gas samples are analyzed by a gas chromatograph equipped with a flame ionization detector (for CH4) and an electron capture detector (for N2O).
Aaltonen et al., 2011. Boreal pine forest floor biogenic volatile organic compound emissions peak in early summer and autumn. Agricultural and Forest Meteorology, 151, 682-691.
Korhonen et al., 2013. Nitrogen balance of a boreal Scots pine forest. Biogeoscience, 10, 1083-1095.
Pihlatie et al., 2007. Gas concentration driven fluxes of nitrous oxide and carbon dioxide in boreal forest soil. Tellus, 59B, 458-469.