Rapid magnetic susceptibility measurement for obtaining superficial soil layer thickness and its erosion monitoring implications

Abstract

Reliable and efficient erosion measurement techniques are essential for monitoring soil erosion rates and patterns, understanding soil erosion mechanisms and developing erosion prediction models. Existing erosion measurement techniques, typically including erosion pins, 3D laser scanners and erosion tracers, have some limitations in practice. A new in situ technique, called the magnetic layer detection (MLD) method, is introduced in this paper. The MLD method determines superficial soil layer thickness (SLT) by detecting the depth of an underground artificial magnetic layer (ML) using a magnetic susceptibility (MS) field probe. It enables a shift from rapid MS measurement to soil erosion or deposition quantification. The results of simulated soil profiles showed the relationship between SLT and volume MS of a target ML exactly followed a universal exponential equation, not sensitive to soil type and ML magnetism level. The theoretical analysis based on the optimally fitted curves showed the accuracy of the MLD method is <±2 mm, and the most effective detection depth ranged from 0 to 80 mm in superficial soil profile. The results of indoor water and wind erosion experiments indicated that the Nash-Sutcliffe efficiency and root mean square error of eroded SLT between the MLD method and the mass weighing method were 76.2% and 0.9 mm for water erosion, respectively and 91.2% and 1.2 mm for wind erosion, respectively. These results indicated the MLD method could rapidly and precisely determine the SLT induced by water erosion and wind erosion. Considering its rapid measurement, low cost, relatively high accuracy, little disturbance to soil erosion process, and no maintenance in monitoring points, the MLD method has great potential for widespread use in soil erosion monitoring.