Water Transport in the Vadose Zone and Hydrological Processes in Soil-Plant-Atmosphere Continuum (SPAC) in West Texas, USA

Water and energy transport in the vadose zone is critical in linking the atmosphere and groundwater system, which plays an important role in the terrestrial hydrological cycle. Although numerous studies have been conducted, the comprehensive understanding of the soil-plant-atmosphere continuum (SPAC) is still limited. In this study, water transport within the SPAC under a semi-arid climate, including rain infiltration and evaporation mechanisms, have been investigated by a combination of on-site monitoring of meteorological and soil water data, isotope tracers, numerical simulations, and remote sensing at a natural rangeland in West Texas. Possible sources of atmospheric moisture in west Texas were studied by the isotope tracers at different seasons and weather conditions. The summer moisture is mainly sourced from the local evapotranspiration (ET) flux and the southeasterly moisture from the Gulf of Mexico, which is isotopically enriched. In contrast, the winter and spring moisture is mainly sourced from the inland ET carried by the westerly wind, which is isotopically depleted. In addition, the high 17O-excess record in atmospheric vapor in the summer of 2022 resulted from the intense evaporation fractionation of the preceding precipitation. Soil water monitoring and HYDRUS simulations show that typical rainfall events in summer 2022 can hardly penetrate 40 cm of the soil profile in semi-arid West Texas. However, the uncommon extended rainfall events in the summer of 2023 penetrated deeper than 100 cm below the soil surface, possibly recharging the Ogallala Aquifer about 15 m below the surface. Isothermal liquid flux was a dominant water component during the early stage of rainfall events. By contrast, thermal vapor flux became a dominant component in the topsoil after a prolonged dry period, and the vapor flux was estimated to contribute as much as 92% of the total water flux of the topsoil. A combination of a new analytical technique and a post-calibration method based on 17O-excess indicator were developed to solve the organic interference issues in Isotope-Ratio Infrared Spectroscopy (IRIS) and the results show that the stable isotope tracers provided good agreement with the numerical simulations of water transports in the rain percolation and identifying the drying fronts in the evaporation processes. In addition, in the vegetated site, the compensation root water uptake can enhance actual transpiration (Ta) by 29% compared to the non-compensation. The Ta contributes approximately 38% and 74% of ETa during the extended rainy period from late May to early June of 2023, and the dry period in late June of 2023, respectively. In summary, this study is one of the first to combine on-site observation, stable isotope tracer, numerical simulation, and remote sensing to investigate the water transport in the SPAC and atmospheric moisture sources in a semi-arid environment. The results from this study can provide valuable scientific information on the soil water dynamics in vadose zone hydrology and terrestrial hydrological cycle in the semi-arid regions, potentially contributing to improved water resources management.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Geology and Geophysics

Grantor

Texas Tech University

Year dc:date.issued

2024

Author dc:creator

• Ling, Xinying

Chair dc:contributor.committeechair

• Horita, Juske

Committee members dc:contributor.committeemember

• Ridley, Moira K.
• Deb, Sanjit
• Goebel, Timothy S.

• soil water transport
• soil-plant-atmosphere continuum
• vadose zone
• HYDRUS-1D
• stable isotope tracers

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/2346/100508

OAI identifier oai:identifier

oai:ttu-ir.tdl.org:2346/100508