Abstract
Information on the spatio-temporal variability of soil moisture in the vadose zone is important to assess groundwater recharge and solute transport in unconsolidated substrate as influenced by biological processes. Time-lapse electrical resistivity imaging (ERI) was used to monitor soil moisture dynamics to a depth of 9 m in a grassland, a grassland encroached by a juniper species (eastern redcedar, Juniperus virginiana), a juniper woodland and an oak forest in the south-central Great Plains, Oklahoma, USA. A site-specific relationship between moisture content and electrical conductivity data was developed for the soil zone, and a perched water zone was monitored at two of the sites. Results showed that (a) change in soil moisture content was linearly correlated to change in electric conductivity in the soil zone; (b) vegetation cover type induced differences in vertical bulk electrical resistivity (ER) profiles and influenced the temporal evolution of soil moisture profiles; and (c) juniper encroachment lowered the water level in the perched groundwater aquifer. Our results suggest land use and vegetation cover type, as opposed to rock properties, controls deep water drainage for the vegetation transition zone. Methods used to measure hydrogeophysical changes, such as ERI, can be used for broader understanding of geological, physical, and biological processes and their links in Earth’s critical zones.
Highlights
Understanding the existence and magnitude of deep drainage and water flowpaths in the vadose zone under contrasting vegetation types is critical to manage groundwater quantity and quality
The grassland site received 97 mm of rain four days prior to electrical resistivity (ER) data acquisition followed by periods of no-rain indicating a wetting-drying cycle (Fig. 3)
Electrical resistivity is inversely related to soil moisture content and this relationship is largely controlled by soil physico-chemical properties such as texture, particle size and geometry of pores, and pore fillings[14, 22, 28]
Summary
Understanding the existence and magnitude of deep drainage and water flowpaths in the vadose zone under contrasting vegetation types is critical to manage groundwater quantity and quality. Electrical resistivity imaging (ERI), a non-intrusive technique, has been used since the 1830’s3 to characterize and monitor water distribution, contaminant plumes, contaminations and remediation, fluid transport, groundwater flow and reactions, subsurface heterogeneity and anisotropy, to map soil texture and to monitor geo-hazards[4,5,6,7,8], but it’s use in monitoring vadose zone soil moisture dynamics and groundwater recharge is still limited[2, 9, 10]. Limited studies have utilized ERI to estimate deep drainage of water and understand the dynamic interaction between vegetation and vadose zone moisture. Alteration in water use patterns and rooting architecture[22] associated with changes in vegetation functional type, such as a transition between grassland and woodlands, is likely to affect the deep percolation dynamics and local recharge processes[17, 23, 24]. While previous research indicated that encroachment by junipers (Juniperus spp.) reduces runoff and soil moisture in the rooting zone[27], we currently do not know how encroachment affects deep moisture profiles which can differ due to factors such as bedrock drainage and perched aquifer in upland catchments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
