Low‐frequency electrical properties of peat

Abstract

[1] Electrical resistivity/induced polarization (0.1-1000 Hz) and vertical hydraulic conductivity (K v ) measurements of peat samples extracted from different depths (0-11 m) in a peatland in Maine were obtained as a function of pore fluid conductivity (s w ) between 0.001 and 2 S/m. Hydraulic conductivity increased with s w (K v / s w 0.3 between 0.001 and 2 S/m), indicating that pore dilation occurs due to the reaction of NaCl with organic functional groups as postulated by previous workers. Electrical measurements were modeled by assuming that ''bulk'' electrolytic conduction through the interconnected pore space and surface conduction in the electrical double layer (EDL) at the organic sediment-fluid interface act in parallel. This analysis suggests that pore space dilation causes a nonlinear relationship between the ''bulk'' electrolytic conductivity (s el ) and s w (s el / s w 1.3 ). The Archie equation predicts a linear dependence of s el on s w and thus appears inappropriate for organic sediments. Induced polarization (IP) measurements of the imaginary part (s 00 surf ) of the surface conductivity (s* surf ) show that s 00 surf is greater and more strongly s w -dependent (s 00 surf / s w 0.5 between 0.001 and 2 S/m) than observed for inorganic sediments. By assuming a linear relationship between the real (s 0 surf ) and the imaginary part (s 00 surf ) of the surface conductivity, we develop an empirical model relating the resistivity and induced polarization measurements to s w in peat. We demonstrate the use of this model to predict (a) s w and (b) the change in K v due to an incremental change in s w from resistivity and induced polarization measurements on organic sediments. Our study has implications for noninvasive geophysical characterization of s w and K v with potential to benefit studies of carbon cycling and greenhouse gas fluxes as well as nutrient supply dynamics in peatlands.

Peatland Volume Mapping Over Resistive Substrates With Airborne Electromagnetic Technology

“…To the best of our knowledge, AEM has never been specifically applied before for the retrieval and characterization of boreal peatlands. As reported for other peatlands (Boon et al, 2008;Comas et al, 2015;Kowalczyk et al, 2017), in this case we find a resistive substrate underlying the peat. Developments of the AEM technology (better system monitoring and early time gates, e.g., Schamper et al, 2014) in the last decade have pushed it toward high-resolution near-surface deposits mapping (i.e., within the first 10 m of depth; Skurdal et al, 2018), making it potentially suitable for studying peatland characteristics, depth, and extension.…”

“…Ground electrical resistivity mapping has been also found successful in several applications (Boon et al, 2008;Comas et al, 2015;Elijah et al, 2012;Kowalczyk et al, 2017). Even though peat usually is electrically more resistive than the substrate (often clays), ground geophysical measurements have shown that there are several examples of peat over resistive unit, both in tropical environments (Comas et al, 2015) and in northern European countries (Boon et al, 2008;Kowalczyk et al, 2017). Even though peat usually is electrically more resistive than the substrate (often clays), ground geophysical measurements have shown that there are several examples of peat over resistive unit, both in tropical environments (Comas et al, 2015) and in northern European countries (Boon et al, 2008;Kowalczyk et al, 2017).…”

Salinity dependence of complex conductivity of unconsolidated and consolidated materials: Comparisons with electrical double layer models

“…Our database is made up of 67 samples with σ 0 0 recorded as a function of salinity from multiple sources (Vinegar and Waxman, 1984;Flath, 1989;Lesmes and Frye, 2001;Slater and Lesmes, 2002;Slater and Glaser, 2003;Comas and Slater, 2004;Breede, 2006;Kruschwitz, 2008;Schröder, 2008;Revil and Skold, 2011). Table 1 summarizes the database, and includes the σ w range investigated, the selected measurement frequency, the source of the data set and a sample description.…”

Improved GPR interpretation through resolution of lateral velocity heterogeneity: Example from an archaeological site investigation

“…Detailed acquisition parameters are listed in Table 2. (Comas and Slater, 2004). a (Hanafy and al Hagrey, 2006).…”