Soil gas concentrations of CO2, CH4, N2O, BVOC and δ13C

Soil air gas concentrations (CO₂, CH₄, N₂O, BVOC) can be determined from gas collectors, which were made of semipermeable PTFE tube (ID: 10.95 ± 0.25 mm Wall: 1.01 ± 0.1 mm IND: 15 ± 10 microns, International Polymer Engineering, Tempe, AZ) and stainless steel tube. A 10 cm-long semipermeable PTFE is connected from both ends to stainless steel tube using airtight stainless steel connectors (Swagelok). The semi permeable part of the collector is buried in the vertical face of soil pit and the stainless steel tubes were led to the surface of the soil. The collector enables through flow or circulation of air when connected to a pump or collection of discrete air samples when collected to syringes with airtight 3-way valves. We installed the air collectors in each soil horizon in 5 soil pits and the pits were filled with the original soil keeping the soil in the original order of excavation in 2011 and in 2011. Soil air CO₂ concentration is also monitored continuously at 1 minute intervals with NDIR CO2 sensors buried inside the soil profile (Vaisala GMM 220, Vaisala Oyj, Helsinki, Finland) close to PIT 100.

Picarro G1101 isotopic CO₂ analyzer started sampling of soil air CO₂ and δ¹³CO₂ profiles from pits 70 and 100 in July 2014. There's sampling for 7.5 min at each depth, starting from pit 100 deepest sample tube. After both pits are done, the instrument is measuring ambient air at ~0.5 m height for one hour, then starts the cycle again. The instrument is also measuring methane but the accuracy and precision are less than stellar.