Abstract
AbstractVegetation 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.
Highlights
Landscape alternation as conversion of natural ecosystems to agricultural lands, or application of soil conservation measures as revegetation for preventing land degradation, have a significant impact on soil water dynamics
Various factors are attributed to the disturbance of the soil water status such as high water demand, larger water-holding capacity of forest soils, deep roots, climate variability and plantation of vegetation in an inadequate environment (Cramer et al, 1999; Rodriguez-Iturbe et al, 2001; Jia and Shao, 2014; Barbeta et al, 2015; Lazo et al, 2021)
Most previous soil water – electromagnetic induction (EMI) studies have targeted relatively shallow variation in electrical conductivity; here we study variation in soil water and σ to depths of 4m
Summary
Landscape alternation as conversion of natural ecosystems to agricultural lands, or application of soil conservation measures as revegetation for preventing land degradation, have a significant impact on soil water dynamics. The conversion of natural vegetation to croplands with shallow rooting systems can increase water levels in unconfined aquifers and mobilizes salts to groundwater (Hancock et al, 2008; Radford et al, 2009; Scanlon et al., 2009; Kurtzman and Scanlon, 2011). Afforestation or revegetation, where trees, grass and shrubs are replanted, were related to depletion of soil water and reduction in groundwater recharge fluxes (Scott and Lesch, 1997; Allen and Chapman, 2001; Zhang et al, 2008; Gates et al, 2011; Huang et al, 2013; Adane et al, 2018; Bai et al, 2020; Ouyang et al, 2021). There is a growing interest in development of monitoring methodologies to improve our knowledge of these processes (Robinson et al, 2008; Krause et al, 2015)
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