Hydrogeophysical characterization of a peatland hillslope in the Belgian High Fens

Despite the fact that peatlands play an important role in climate regulation, biodiversity support, water regulation, carbon storage etc., they are understudied biotopes. The objective of this study, conducted in the Belgian High Fens, was to characterize and understand the soil surface and subsurface long-term characteristics which are conditioning the shorter-term hydrogeophysical processes. To this end, Ground-Penetrating Radar (GPR) and Electromagnetic Induction (EMI) were used and this source of information was complemented with soil coring and in situ soil water conductivity measurements. The GPR and soil coring allows to reconstruct the soil structure which is composed of a layer of approximately 80 cm of peat that developed on an impermeable clay layer issued of the slate bedrock decomposition. The EMI shows a bulk soil electrical conductivity (EC) around 10 mS/m, which is consistent with the relatively low values observed in other peat studies. The EC is lower in the slope, where the water fluxes are higher. The EC was higher (of about 3 mS/m) in summer than in spring. The EC values and dynamics seem to be mainly controlled by the ion content of the soil solution. This ion content is controlled by the water fluxes on the site evacuating the ions downhill to a river. The soil water content is believed to have a low impact on the EC as the site is quite saturated most of the year. No clear correlation was found between the EC patterns and the soil structure. A novel drone-borne, low-frequency GPR (< 50 MHz) is being applied on the study site to allow for a faster and easier EC mapping. This study highlights the major influence of the ion content on the EC patterns and dynamics in a peat site. This study will also be a basis to interpret further measurements that will be made on the site (water, soil and vegetation monitoring).