Abstract
Abstract. Electromagnetic induction (EMI) measurements are widely used for soil mapping, as they allow fast and relatively low-cost surveys of soil apparent electrical conductivity (ECa). Although the use of non-invasive EMI for imaging spatial soil properties is very attractive, the dependence of ECa on several factors challenges any interpretation with respect to individual soil properties or states such as soil moisture (θ). The major aim of this study was to further investigate the potential of repeated EMI measurements to map θ, with particular focus on the temporal variability of the spatial patterns of ECa and θ. To this end, we compared repeated EMI measurements with high-resolution θ data from a wireless soil moisture and soil temperature monitoring network for an extensively managed hillslope area for which soil properties and θ dynamics are known. For the investigated site, (i) ECa showed small temporal variations whereas θ varied from very dry to almost saturation, (ii) temporal changes of the spatial pattern of ECa differed from those of the spatial pattern of θ, and (iii) the ECa–θ relationship varied with time. Results suggest that (i) depending upon site characteristics, stable soil properties can be the major control of ECa measured with EMI, and (ii) for soils with low clay content, the influence of θ on ECa may be confounded by changes of the electrical conductivity of the soil solution. Further, this study discusses the complex interplay between factors controlling ECa and θ, and the use of EMI-based ECa data with respect to hydrological applications.
Highlights
Electromagnetic induction (EMI) methods are widely used for soil mapping, as they allow fast and relatively low-cost surveys of soil apparent electrical conductivity (ECa) over areas up to several squared kilometers in size (McNeil, 1980)
As discussed earlier in the text, intrinsic limitations exist in the EMI measurement technique which may limit the comparability of absolute ECa values; we did not attempt to interpret the temporal changes of ECae from one measurement date to the other, but rather we focus on the ECae–θd relationship for every single measurement date and depth of monitoring which, provides useful hints about the strength and persistence of the relationship
Repeated EMI surveys were conducted on a hillslope site within the Schäfertal catchment, of which soil properties and soil moisture dynamics were known
Summary
Electromagnetic induction (EMI) methods are widely used for soil mapping, as they allow fast and relatively low-cost surveys of soil apparent electrical conductivity (ECa) over areas up to several squared kilometers in size (McNeil, 1980). The use of non-invasive geophysical techniques for soil mapping is very attractive, the dependence of the measured ECa on a number of parameters complicates any interpretation to determine soil properties or states (Robinson et al, 2012). A firm understanding of the spatial and temporal variability of soil electrical conductivity (EC) and an appreciation for its highly complex interactions with static soil properties and dynamic state variables, at low-salt concentrations, is needed (Sudduth et al, 2001, 2005; McCutcheon et al, 2006), and it is helpful for understanding when EMI
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