Mapping Subsurface Stratigraphy Controlling Groundwater-Surface Water Interactions and Estimating Associated Subsurface Gas Content in a Degraded Fen

Rewetting efforts to restore anthropogenically degraded peatlands across Germany aim to curb the rapid release of carbon gases onset from peat desaturation. To monitor peat saturation across remediation efforts aimed to stabilize carbon-cycling, it is paramount to understand the hydrology controlling flow through these systems. Underlying mineral sediment stratigraphy controls peatland water levels, with more permeable structures altering flowpaths and sourcing minerogenous groundwater. In this study we examined the Zarnekow wetland, a degraded fen in northeast Germany, using a suite of electrical geophysical methods to map the stratigraphic interfaces between the peat and underlying mineral sediments. Rought terrain ground-penetrating radar (GPR) and towed transient electromagnetic induction surveys were deployed to characterize the mineral sediment interface across the fen. Variability in the mineral sediment interface was then compared to hydrological temperature signals indicative of groundwater upwelling, allowing for inferences about the stratigraphic controls on groundwater flow. An extended transect within the survey area was selected for targeted GPR surveys using both common offset and common midpoint geometries. These additional data allowed for estimates of the subsurface gas content. Time-domain induced polarization was deployed over the same transect to examine contrasts between the real and imaginary components of the complex conductivity. Initial results from the focused electrical surveys provide robust spatial insight into the gas distribution within the Zarnekow wetland. This study bolsters the use of electrical geophysics for seasonal monitoring of gas migration in the subsurface, informing ongoing peatland remediation efforts.