Determination of the gas diffusion coefficient of a peat grassland soil.

摘要

Peatland habitats are important carbon stocks that also have the potential to be significant sources of greenhouse gases, particularly when subject to changes such as artificial drainage and application of fertilizer. Models aiming to estimate greenhouse gas release from peatlands require an accurate estimate of the diffusion coefficient of gas transport through soil (D_s). The availability of specific measurements for peatland soils is currently limited. This study measured D_s for a peat soil with an overlying clay horizon and compared values with those from widely available models. The D_s value of a sandy loam reference soil was measured for comparison. Using the Currie (1960) method, D_s was measured between an air-filled porosity ( epsilon ) range of 0 and 0.5 cm3 cm-3. Values of D_s for the peat cores ranged between 3.2x10-4 and 4.4x10-3 m2 hour-1, for loamy clay cores between 0 and 4.7x10-3 m2 hour-1 and for the sandy reference soil they were between 5.4x10-4 and 3.4x10-3 m2 hour-1. The agreement of measured and modelled values of relative diffusivity (D_s/D₀, with D₀ the diffusion coefficient through free air) varied with soil type; however, the Campbell (1985) model provided the best replication of measured values for all soils. This research therefore suggests that the use of the Campbell model in the absence of accurately measured D_s and porosity values for a study soil would be appropriate. Future research into methods to reduce shrinkage of peat during measurement and therefore allow measurement of D_s for a greater range of epsilon would be beneficial.