Electromagnetic Conductivity Imaging of Soil Salinity in an Estuarine–Alluvial Landscape

Abstract

In coastal–estuarine agricultural landscapes, shallow and often saline water tables are problematic because they limit agricultural productivity. To understand the dynamics of rainfall events and tidal influences, natural resource management baseline data need to be collected to describe the heterogeneous nature of the soil and interactions with fluctuating groundwater tables, particularly in areas characterized by coastal acid sulfate soil. Electromagnetic induction instruments are increasingly being used because they measure the apparent soil electrical conductivity (ECa, mS m−1), which is related to soil salinity and hydrologic properties. Our aim was to demonstrate how the ECa data from a DUALEM‐421 can be used in conjunction with inversion software (EM4Soil) to develop electromagnetic conductivity images, which are two‐dimensional cross‐sections of estimates of the true electrical conductivity (σ, mS m−1). We show how the estimates of σ can be related to the electrical conductivity of a saturated soil paste extract (ECe, dS m−1) across an estuarine landscape and situated within Quaternary fluvial sediments adjacent to Rocky Mouth Creek on the far northern coast of New South Wales, Australia. Our results indicate that a good linear relationship (r2 = 0.70) can be established between σ and ECe, and the results reflect the existing soil landscape units.