Predicting the presence and release of free-phase gas in a wetland

Abstract

This study sought to improve the understanding of methane ebullition from wetlands by measuring total dissolved gas pressure (Ptdg), volumetric gas content, water pressure, and methane flux from surface chambers between July and September in the shallow part of a wetland. Capillary pressure, which is often ignored in estimating bubbling pressure, contributed up to 5% of the Pbub at shallow depths. Estimated bubbling pressure (Pbub(est)) was a better estimate of free-phase gas than Pbub(ave) given observed variations in Patm and Pw of up to 20 mm Hg. Although Ptdg increased with depth, free-phase gas presence did not vary with depth or time suggesting differential rates of production, retention, and release of gas with depth. Heterogeneities in the peat structure, most significantly the presence of a dense peat layer (~50 cm), contributed to limited agreement between gas-monitoring methods used.