Soil moisture and electrical conductivity relationships under typical Loess Plateau land covers

• Published in: Vadose zone journal 2022-01, Vol.21 (1), p.n/a
• Main Authors: Turkeltaub, Tuvia, Wang, Jiao, Cheng, Qinbo, Jia, Xiaoxu, Zhu, Yuanjun, Shao, Ming‐An, Binley, Andrew
• Format: Article
• Language: English
• Subjects: China; Depth; Electrical conductivity; Electrical resistivity; Electromagnetic induction; fallow; Flow distribution; Flow pattern; Geophysical exploration; Geophysical methods; geophysics; Land cover; Moisture content; neutrons; Parameter sensitivity; Pasture; pastures; Pore water; shrubs; Soil conductivity; Soil conservation; soil electrical conductivity; Soil erosion; Soil moisture; Soil water; soil water content; Solute transport; Solutes; Soybeans; Subsurface water; Sustainability; Vadose water; vadose zone; Variability; Vegetation; Vegetation changes; Vulnerability; Water conductivity; Water consumption; Water content; Water distribution; Water engineering; Water flow
• ISSN: 1539-1663; 1539-1663
• DOI: 10.1002/vzj2.20174

Vegetation changes that are driven by soil conservation measures significantly affect subsurface water flow patterns and soil water status. Much research on water consumption and sustainability of newly introduced vegetation types at the plot scale has been done in the Loess Plateau of China (LPC), typically using local scale measurements of soil water content (SWC). However, information collected at the plot scale cannot readily be up‐scaled. Geophysical methods such as electromagnetic induction (EMI) offer large spatial coverage and, therefore, could bridge between the scales. A noninvasive, multicoil, frequency domain, EMI instrument was used to measure the apparent soil electrical conductivity (σa) from six effective depths under four typical land‐covers (shrub, pasture, natural fallow, and crop) in the north of the LPC. Concurrently, SWC was monitored to a depth of 4 m using an array of 44 neutron probes distributed along the plots. The measurements of σa for six effective depths and the integrated SWC over these depths, show consistent behavior. High variability of σa under shrub cover, in particular, is consistent with long term variability of SWC, highlighting the potential unsustainability of this land cover. Linear relationships between SWC and σa were established using cumulative sensitivity forward models. The conductivity–SWC model parameters show clear variation with depth despite lack of appreciable textural variation. This is likely related to the combined effect of elevated pore water conductivity as was illustrated by the simulations obtained with water flow and solute transport models. The results of the study highlight the potential for the implementation of the EMI method for investigations of water distribution in the vadose zone of the LPC, and in particular for qualitative mapping of the vulnerability to excessive vegetation demands and hence, unsustainable land cover. Core Ideas An increasing trend in apparent electrical conductivity (ECa) corresponds with the increase in soil water content (SWC) under four typical land‐covers. Linear relationships between SWC and ECa were established using the cumulative sensitivity model. Elevated pore water conductivity effects the relationship between conductivity and SWC.