Decimeter-Scale 3-D Heterogeneity of Soil Physical, Hydraulic and Pore-Geometry Properties in a Norwegian Field Soil.

Heterogeneous water flow in undisturbed soils is a complex natural occurrence that is challenging to quantify due to changes in soil hydraulic properties across different spatial scales. The use of geophysical methods, such as Electrical Resistivity Tomography (ERT), provides minimally-invasive approximation of the spatial heterogeneity of the soil. This spatial distribution can then be combined with hydraulic properties to inform a model. We conducted an experiment involving different field and laboratory sensory techniques and measurements with the objective of examining decimeter-scale 3D functional heterogeneity and its physical drivers in natural soil. The location of an Intensively Investigated Soil Volume (IISV) with dimensions of 2x1x0.8m was selected from surface ERT runs performed at two sequential resolutions on a clay loam soil in the Gryteland catchment near Ås, Norway. The first run was used to find an area of varied electrical resistivity within a 23.5x11.5m area with 0.5m electrode spacing; the second run measured electrical resistivity over a 4.7x1m area using 0.1m electrode spacing. Parallel trenches were excavated on the two longest sides of the IISV to allow horizontal installation of 20 pairs of TDR probes and tensiometers into distinct features found in the higher resolution ERT run. We monitored water content, temperature, electrical conductivity and pressure potential at 10 minute intervals for two weeks. After completion of the data collection the investigated volume was intensively sampled for bulk density (n=30), the measurement of soil hydraulic properties (n=89), of which 25 were also used for CT scanning and subsequent image analysis. We present the resulting data, measured from the micro-scale (X-CT) to the mesoscale (ERT) with focus on the spatial correlation length of soil physical structure and flow phenomena and a way to cluster/upscale soil physical, morphological and hydraulic properties for use in 3D simulation modeling.