Date of Award

2022-12-01

Degree Name

Master of Science

Department

Geological Sciences

Advisor(s)

Mark Engle

Abstract

Caliche or pedogenic calcium carbonate (CaCO3) layers are a common feature of arid soils, but the environmental controls on their distribution are not fully understood. Caliche layers are thought to play an important role in shallow subsurface water storage and movement, due to their water retention capacity and ability to impede vertical water transport (Hennessy et al., 1983). Therefore, caliche distribution and stability play a role in controlling water distribution in arid lands. However, due to its largely subsurface nature, caliche can be difficult to investigate and map without significant effort. I hypothesize that noninvasive geophysical methods, such as ground-penetrating radar (GPR), may be an ideal approach to characterize shallow caliche layers as means to understand controls on its distribution.The goals of this research are to: 1) apply GPR to document the distribution and nature of subsurface caliche layers; 2) investigate the physical and chemical stability of caliche relative to its distribution at specific dryland sites; 3) examine the role of caliche layers in regulating soil water storage and movement. This research was conducted at two sites (one piedmont and one playa site) in the Chihuahuan desert at Jornada Experimental Range (JER) near Las Cruces, New Mexico. Seasonal GPR data have been collected to determine ideal conditions (e.g., soil moisture content) to map caliche with GPR in dryland environments. Water movement through and soil erosion above caliche layers were used as indicators of its physical and chemical stability, respectively, to understand caliche's chemical and physical stability across the two sites. Vertical water fluxes and soil moisture content in the shallow vadose zone were investigated using time series data from vertical profiles of Time Domain Reflectometry (TDR) soil moisture probes at multiple locations in the study sites. Surface stability was assessed through the implementation of the Revised Universal Soil Loss Equation (RUSLE), which has been largely used in soil science to determine soil erodibility (Benavidez et al., 2018; Chandramohan et al., 2002). GPR radargrams successfully identified the top surface of the shallowest caliche layer; those depths correlate with hand augering observations. Reflectors in GPR radargrams that are roughly coincident with the bottom of the caliche layer were also observed in several of the soil profiles. On the piedmont site, caliche was both physically and chemically stable on the Jornada Ⅰ surface (JⅠ), while it is physically but non chemically stable on the Organ surface (Qo). This research has demonstrated the utility of GPR to investigate the spatial distribution of caliche layers, and their presence relative to indicators of physical surface stability and chemical caliche stability. It also points toward the processes that lead to caliche formation or erosion in dryland environments.

Language

en

Provenance

Received from ProQuest

File Size

66 p.

File Format

application/pdf

Rights Holder

Nohemi Valenzuela Garay

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