Determination of the gas diffusion coefficient of a peat grassland soil

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 (E) range of 0 and 0.5cm(3) cm(-3). Values of D-s for the peat cores ranged between 3.2x10(-4) and 4.4x10(-3) m(2) hour(-1), for loamy clay cores between 0 and 4.7x10(-3) m(2) hour(-1) and for the sandy reference soil they were between 5.4x10(-4) and 3.4x10(-3) m(2) hour(-1). The agreement of measured and modelled values of relative diffusivity (D-s/D-0, with D-0 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 E would be beneficial.