Using electromagnetic induction method to reveal dynamics of soil water and salt during continual rainfall events

The spatial patterns and dynamics of soil water and salt at the field scale between rainfall events are not well understood due to a lack of appropriate instruments for measurements. In this study, we conducted time series EMI surveys and then mapped apparent electrical conductivity (ECa) to estimate the relative changes in soil water and salt in an Achnatherum splendens steppe ecosystem in Qinghai Lake watershed, China. The results indicated that ECa could be used as a surrogate for interpreting changes of water and salt content in soil. The ECa images clearly showed that ECa values increased rapidly after rainfall events, and the increased amplitudes of ECa values in soils under A. splendens (AS) were obviously greater than that of soil in the interspaces between A. splendens tussocks (IAS). This demonstrated that rainwater infiltrated faster and in greater quantity into the soils under AS because of their coarse-textured surface soils with greater macroporosity and higher hydraulic conductivity as compared to the interspace soils. Moreover, the increasing salinity in AS and decreasing salinity in IAS after rainfall events suggested that overland flow might perhaps have occurred from the interspaces into A. splendens areas. The temporal stability of ECa maps demonstrated that there was great soil variability at the study plot, especially in soil salt. This study highlighted that the time series ECa images could qualitatively capture dynamics of soil water and salt at the field scale after rainfall events, and it linked the dynamics of soil water and salt to vegetation variability.