Distribution and causes of intricate saline-sodic soil patterns in an upland South Australian hillslope

Abstract

We describe a soil–landscape investigation conducted in a South Australian upland hillslope (128 ha) to understand the distribution and causes of saline–sodic soil patterns using convenient, ground-based geophysical surveys of the hillslope. These surveys included: (i) EM31 for deep (~6 m) apparent electrical conductivity (ECa) patterns, (ii) EM38 for shallow (>1.5 m) ECa patterns, and (iii) Bartington MS2-D loop sensor for surface volume magnetic susceptibility (κ) patterns. From these surveys we inferred hillslope distributions of: (i) deep (~6 m) concentrations of salinity associated with deep groundwater systems and deposits of magnetic gravels (dominated by maghemite and hematite) (EM31 sensor); (ii) shallow (<1.5 m) soil salinity (EM38 sensor); and (iii) preservation of pedogenic magnetic materials (e.g. maghemite and hematite) (MS2-D loop sensor). We also describe terrain analysis to locate near-surface hydropedological patterns using topographic wetness index. When combined in 3D geographic information system, strong visual matches were identified between patterns in: (i) geophysical surveys, (ii) terrain, and (iii) soil survey data, thus allowing integrated interpretations of soil–landscape pedogenic processes to be made on a whole-of-landscape basis. Such mechanistic interpretations of soil–landscape processes reveal and map intricate saline and sodic soil–regolith patterns and groundwater and fresh surface water flow paths that were not revealed during a previous traditional soil survey.