Tong, C.; Huang, J., and Jia, Y., 2015. Small-scale spatial variability of soil methane production potential and porewater characteristics in an estuarine Phragmites australis marsh.

High temporal and spatial variability is a problem when quantifying methane flux from wetland soils. Spatial variability of methane production at the landscape scale has been investigated for different wetlands, but few studies have examined soil methane production at the small scale. Here, we investigated small-scale spatial patterns of soil methane production potentials and concentrations of porewater acetate, dissolved CO₂, , , and soil dissolved organic carbon (DOC) in a brackish Phragmites australis marsh of the Min River estuary, southeast China. Sampling was performed for an area of 1.6 × 1.6 m to a depth of 30 cm (5-cm intervals) using a grid of 0.4 m resolution. Data were interpolated by an inverse distance moving average weighted method. Large differences in soil methane production potentials were detected between each grid across lateral space. Coefficients of variation (CVs) often exceeded 100%, indicating very high spatial variability in methane production potentials on the small scale in the horizontal direction in brackish P. australis marsh. Results also showed no significant spatial autocorrelation in methane production potentials at the small scale. Topsoil (0–5 cm) showed the greatest methane production potentials (1.07 μg g⁻¹ d⁻¹). The CVs of acetate and dissolved CO₂ concentrations were always <50%, except in the topsoil, which indicates a lower spatial variability of the concentrations of substrates compared with methane production potentials. Spatial autocorrelation in porewater acetate and dissolved CO₂ also was not strong at the small scale. The mean concentrations of acetate and soil DOC were indistinguishable (p > 0.05) between the six depth layers. The results of this study confirm methane production is probably one of the biogeochemistry processes bearing the most distinct spatial variability in soil.