Permafrost Mapping with Electrical Resistivity Tomography: A Case Study in Two Wetland Systems in Interior Alaska

Abstract

Surface-based 2D electrical resistivity tomography (ERT) surveys were used to characterize permafrost distribution at wetland sites on the alluvial plain north of the Tanana River, 20 km southwest of Fairbanks, Alaska, in June and September 2014. The sites were part of an ecologically-sensitive research area characterizing biogeochemical response of this region to warming and permafrost thaw, and the site contained landscape features characteristic of interior Alaska, including thermokarst bog, forested permafrost plateau, and a rich fen. The results show how vegetation reflects shallow (0–10 m depth) permafrost distribution. Additionally, we saw shallow (0–3 m depth) low resistivity areas in forested permafrost plateau potentially indicating the presence of increased unfrozen water content as a precursor to ground instability and thaw. Time-lapse study from June to September suggested a depth of seasonal influence extending several meters below the active layer, potentially as a result of changes in unfrozen water content. A comparison of several electrode geometries (dipole-dipole, extended dipole-dipole, Wenner-Schlumberger) showed that for depths of interest to our study (0–10 m) results were similar, but data acquisition time with dipole-dipole was the shortest, making it our preferred geometry. The results show the utility of ERT surveys to characterize permafrost distribution at these sites, and how vegetation reflects shallow permafrost distribution. These results are valuable information for ecologically sensitive areas where ground-truthing can cause excessive disturbance. ERT data can be used to characterize the exact subsurface geometry of permafrost such that over time an understanding of changing permafrost conditions can be made in great detail. Characterizing the depth of thaw and thermal influence from the surface in these areas also provides important information as an indication of the depth to which carbon storage and microbially-mediated carbon processing may be affected.

Best practices for using electrical resistivity tomography to investigate permafrost

“…This array can also utilize multichannel instrument capabilities to reduce data acquisition time, as can any array that involves multiple potential measurements for a common current pole/dipole. Several studies compare different array types and their abilities to resolve permafrost features (e.g., [49][50][51] ). Some practitioners collected data using multiple array types and amalgamated the data to take advantage of the strengths of each array (e.g., 51 ).…”

Time-Lapse Electrical Resistivity Tomography (TL-ERT) for Landslide Monitoring: Recent Advances and Future Directions

“…In the last 20 years, more than 200 papers have been published on ISI journals (Figure 1). The TL-ERT method found an impressive number of applications crossing different disciplines, from hydrogeology [9][10][11][12] to agriculture [13][14][15][16], from engineering geology [17][18][19][20] to geohazards [21][22][23][24], from CO2 storage [25] to the study of the effects of the climate changes on soil and near subsurface [26][27][28][29].…”

Near‐surface geophysical imaging of a thermokarst pond in the discontinuous permafrost zone in Nunavik (Québec), Canada

“…Geophysical methods seem to be an appropriate way to achieve these objectives, because they can provide detailed spatial information about the physico‐chemical and thermal properties of the ground, in both vertical and horizontal directions. Numbers of studies have proven the efficiency of electrical resistivity tomographies (ERTs) to distinguish between unfrozen, frozen, or ice‐rich areas, at the landscape scale 13–16 . Indeed, the electrical resistivity of a water‐saturated medium varies over several orders of magnitude when the pore water freezes.…”

“…Numbers of studies have proven the efficiency of electrical resistivity tomographies (ERTs) to distinguish between unfrozen, frozen, or ice-rich areas, at the landscape scale. [13][14][15][16] Indeed, the electrical resistivity of a water-saturated medium varies over several orders of magnitude when the pore water freezes. However, as the electrical resistivities of ice and air are quite similar, it is less straightforward to distinguish unsaturated from icefilled porous media on the basis of the ERT values alone.…”