Continuous measurement of vertical distribution of CO2 concentration and its isotopic signature in a beech and a pine forest soil

Hubert Jochheim1, Stephan Wirth2
1 Institute of Landscape Systems Analysis, Leibniz-Centre for Agricutlural Landscape Research
2 Institute of Landscape Biogeochemistry, Leibniz-Centre for Agricutlural Landscape Research

P 3.5 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

A new approach was applied for the continuous detection of vertical profiles of CO2 concentrations and δ13C-CO2 signatures in soil.

Two ICP Forest intensive monitoring sites were studied, a beech forest located at Beerenbusch, and a pine forest located at Kienhorst, both in Brandenburg, Germany. CO2 concentrations in the air-filled pores of soil were measured in -10cm, -20cm, -30cm and -100 cm depths (3 replicas each), as well as below the humus layer and on top of soil surface based on a closed cycle of hydrophobic, gas-permeable porous polypropylene tubings. At both sites, soil moisture and temperature (TRIME probes) were measured in respective soil depths. During a measurement campaign, a mobile CO2 analyzer device, consisting of 16 pumps, 16 NDIR CO2-sensors (1.000 – 50.000 ppm), a 16-position multiplexer, and a data logger was connected to an isotope CO2 analyzer (CRDS, Picarro). Soil gas was circulated in a closed loop from the membrane tube passing a multiplexer system into the gas measurement setup. Special interest was directed to the assessment of temporal dynamics of soil CO2 concentrations in combination with monitoring of soil temperature and moisture in order to explain the underlying mechanisms. Isotopic signatures (δ13C-CO2) were monitored in order to trace sources of soil organic carbon. Furthermore, the effect of root density along a trunk distance gradient on soil CO2 concentration was assessed.

Our results after one year of measurements provided evidence for distinct vertical CO2 concentration gradients with seasonal dynamics. Varying impacts of soil temperature and moisture on CO2 concentration were revealed. Along distance from the tree trunk, increasing CO2 concentrations were found in -10cm and -20cm soil depths. The δ13C of soil CO2 was variable over time, and displayed a gradient with soil depth.

Letzte Änderung 04.04.2014