Atmospheric pressure drives changes in the vertical distribution of biogenic free-phase gas in a northern peatland

Abstract

[1] Atmospheric pressure (Patm) is known to regulate methane emissions from northern peatlands. However, recent conceptual models differ in how gas production and release occurs in shallow (defined here as less than 1 m depth) versus intermediate to deep peat soils (i.e., more than 1 m depth). We used ground penetrating radar (GPR) measurements to non-invasively estimate the vertical distribution of free-phase gas and the dependence of this distribution on atmospheric pressure in a northern peatland. Variations in the travel time of the electromagnetic wave to three interfaces in the peat column were used in conjunction with deformation rod data and a petrophysical model relating electromagnetic wave velocity to free-phase gas content to model changes in the vertical distribution of free-phase gas over time. We found a negative linear relation between changes in free-phase gas content and changes in Patm for shallow peat soils and a positive linear relation for deeper soils. Our results suggest that (1) free-phase gas content confined in deep peat soils is larger and less variable to changes in Patm than gas in shallow/intermediate peat soils; (2) increases in Patm result in gas release from shallow peat soils into the atmosphere (i.e., rapid ebullition); and (3) decreases in Patm result in upward gas movement from intermediate layers to replenish shallow layers. Our results suggest that changes in Patm drive changes in the vertical distribution of free phase gas in peat soil and regulate methane ebullition from peat soils to the atmosphere. Our data shows a relationship between free phase gas and depth that may be due to changes in peat properties or increasing water pressure with depth.