Temporal mapping of the three-dimensional spatial distribution of solute transport in soils is needed for an improved understanding of the underlying processes. Numerous studies have confirmed that Brilliant Blue imaging provides spatially highly resolved information on solute transport in soils. A drawback of the method, however, is its destructive character, which prevents three-dimensional mapping of the temporal evolution of Brilliant Blue plumes or fronts. In this study, we determined that the negative ionic charge of the Brilliant Blue molecule for moderately acid and basic environments provides an electrical conductivity contrast that can be detected by means of time domain reflectometry (TDR) and electrical resistivity tomography (ERT). Time-lapse ERT supplies three-dimensional spatiotemporally resolved image data through minimally invasive measurements but with limited spatial resolution. A joint application of Brilliant Blue imaging and (time-lapse) ERT offers potential benefits such as ERT image validation by dye staining, spatiotemporally resolved Brilliant Blue displacement studies, and improved ERT inversion regularization based on Brilliant Blue image-derived solute plume or front characteristics. This study illustrates the efforts needed to quantitatively relate Brilliant Blue concentration and electrical conductivity as well as the potential and limitations of noninvasive smoothness-constrained ERT for solute imaging in soils.

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