Free phase gas processes in a northern peatland inferred from autonomous field‐scale resistivity imaging

Abstract

The mechanisms that control free phase gas (FPG) dynamics within peatlands, and therefore estimates of past, present, and future gas fluxes to the atmosphere remain unclear. Electrical resistivity imaging (ERI) is capable of autonomously collecting three‐dimensional data on the centimeter to tens of meter scale and thus provides a unique opportunity to observe FPG dynamics in situ. We collected 127 3‐D ERI data sets as well as water level, soil temperature, atmospheric pressure, and limited methane flux data at a site in a northern peatland over the period July–August 2013 to improve the understanding of mechanisms controlling gas releases at a hitherto uncaptured field scale. Our results show the ability of ERI to image the spatial distribution of gas accumulation and infer dynamics of gas migration through the peat column at high (i.e., hourly) temporal resolution. Furthermore, the method provides insights into the role of certain mechanisms previously associated with the triggering of FPG releases such as drops in atmospheric pressure. During these events, buoyancy‐driven gas release primarily occurs in shallow peat as proposed by the “shallow peat model.” Releases from the deeper peat are impeded by confining layers, and we observed a large loss of FPG in deep peat that may likely represent a rupture event, where accumulated FPG escaped the confining layer as suggested by the “deep peat model.” Negative linear correlations between water table elevation and resistivity result from hydrostatic pressure regulating bubble volume, although these variations did not appear to trigger FPG transfer or release.

Understanding Peat Soil Deformation and Mechanisms of Peat Collapse Across a Salinity Gradient in the Southwestern Everglades

“…Numerous studies have used ERI to study peatland attributes and stratigraphy (e.g. Comas et al., 2004, 2011, 2015; Kettridge et al., 2008; Silvestri et al., 2019; Slater & Reeve, 2002; Terry et al., 2016; Uhlemann et al., 2016) and ERI has also been successfully employed to investigate karst features in the near subsurface (e.g. Chalikakis et al., 2011; Majzoub et al., 2016; Park et al., 2013; Zhou et al., 2002).…”

Advancing hydrological process understanding from long‐term resistivity monitoring systems

“…They also highlight some of the challenges concerning changes in spatial regularization within the data inversion process: a progressive increase in spatial regularization over time was required in order to match independently observed responses in wells. Terry et al (2016) used LTRM to investigate carbon gas dynamics in peatlands, focusing on improving understanding of the production and transport of methane-rich gasses within a peatland and to the atmosphere.…”

In-situ marine gas hydrate production methane leaks electrical monitoring system

“…Breen et al (2012) studied the ability of electrical resistivity tomography (ERT) to describe the spatial distribution of shallow gas and to estimate gas saturation by using twodimensional model experiments [12] . Resistivity imaging method has many practical applications in monitoring gas storage and migration, gas content in pore space [13][14][15] . Both model and in-situ experiments show that resistivity imaging technology can effectively describe the spatial distribution of non-conductive medium in pore space and preliminarily estimate its saturation.…”