Delineation and description of soil horizons using ground-penetrating radar for soils under boreal forest in Central Karelia (Russia)

This article focused on studying the landscape-scale spatial variation of boreal forest soils in data-scarce areas using ground-penetrating radar (GPR). An important goal of the research was to discuss correlations between attributes of the soil profile under boreal forest and GPR data. We detected the soil horizons of Entic Podzols and determined their attributes based on a GPR transect with a 400 MHz antenna unit. GPR cross-section showed the soil thickness variation over the transect being 18.8 cm to 44.7 cm. The mean depth for the soil's lower boundary from sounding was 23.1 cm versus the probing of 24 cm. The fieldwork research has revealed GPR patterns for different ecological settings: typical forest, paludified forest, and felling area. We investigated the GPR applicability for delineating organic layers in soils and considered quantifying soil organic carbon content (SOC) relying on GPR attributes. To achieve this purpose, we have surveyed Albic Podzols with a 1,700 MHz antenna unit considering vegetation cover. The resolution of GPR was ±1 cm, which made to determine relatively thin horizons. GPR reflected signal amplitudes demonstrated sensitivity to SOC variations in the organic layers. The obtained relationship between SOC and GPR attributes indicates the possibility of determining the carbon storage variations in situ. However, the problem is to substantiate the mechanism of the SOC influence on the signature of the GPR traces. The findings prove that GPR is a tool for predicting the state and scope of the transformation of sandy forest soils. GPR cross-sections can be the basement for a novel approach for forest soil mapping on a landscape scale. In prospect, digital soil mapping can include a sequence of methods: remote sensing – GPR – manual probing. Admittedly, alignments between soil characteristics and GPR attributes are needed to identify the capabilities and limitations of the method.