Date of Award

2022-08-01

Degree Name

Master of Science

Department

Geology

Advisor(s)

Hugo A. Gutierrez-Jurado

Abstract

Recent studies have suggested an ecohydrological separation of water exists in the northern Chihuahuan Desert, where vegetation types, rainfall regimes, and location in the terrain seem to determine the type of water (e.g. isotopically depleted or enriched in 18O and 2H) plants are able to source and use throughout their growing cycle. That work found evidence of creosote (Larrea tridentata) and mesquite (Prosopis glandulosa) using tightly bound soil water at both a site on an ephemeral channel and a site in higher elevated flat area because the isotopic signature of plant water at the beginning of the study did not match that of precipitation but matched the soil samples. This behavior suggested tightly bound soil water was utilized and was sufficient to meet dry period vegetation demand. Additionally, soils from the channelized site were shown to become both enriched and depleted faster in δ18O and 2H than the flatter site, showing clear differences in hydrologic dynamics of the shallow soils possibly due to the influence of runoff on the channel soils. However, questions remain about the influence of soil properties and vegetation competition on the water sourcing dynamics of desert vegetation. This study will be adding two vegetation dense, finer soil sites to the existing low-lying channel sites and higher, flatter piedmont sites. This study uses stable water isotope data to determine the relationship between subsurface water storage and desert vegetation in a dry piedmont in the Northern Chihuahuan Desert. Soil texture analyses were conducted on an instrument that measures suspension pressure, called PARIO. Vegetation xylem water was extracted using the cryogenic method to avoid isotopic fractionation. Soil samples were processed using the induction module (IM) attachment in the Picarro L2130-i CRDS. Quantitative observations of δ18O and Deuterium from precipitation, soil water, and stem water samples from Creosote Bush (Larrea tridentata), Honey Mesquite (Prosopis glandulosa), Tarbush (Flourensia cernua), and Poaceae sp. were obtained using laser-based cavity vi ringdown spectroscopy during two growing cycle periods for a total of 37 months in a piedmont location within the western side of the Jornada Experimental Range (JER). The results of this study at the JER show that there are factors influencing the available water for the four desert vegetation species studied throughout their growing season. When assessing the soil texture influence on water availability, it is apparent that VD/FS (Vegetation Dense/Finer Soil) areas experience little evaporation due to their finer soil texture and possibly increasing their soil water residence time. When assessing the vegetation competition influence on water sourcing, we observed that the plants have different water sources strategies depending on the site and species. The isotopic signature of the stem water in the vegetation at the VD/FS areas tend to follow that of precipitation more closely than those of the vegetation on the other sites. This may be due to the inability of vegetation in the VD/FS areas to obtain water past the shallow soils due to the presence of a highly indurated caliche interfering with deeper infiltration. At the FA (Flat Area), honey mesquite tends to show a more relatively isotopically depleted water suggesting a deeper source in the soil profile, whereas, creosote shows a more enriched water resembling that found on shallower soil. The CA (Channel Area) shows that the vegetation may have a similar source in the soil profile. We also observed that landscape may have an influence on water availability. The channel area has a wide range of isotopic values that may indicate additional runoff from upstream that is combining with water previously in the soil profile. The interpretation of these results illuminates the plant water use dynamics and strategies of highly resilient desert vegetation communities as affected by the structure of the shallow critical zone.

Language

en

Provenance

Recieved from ProQuest

File Size

91 p.

File Format

application/pdf

Rights Holder

Martha Elizabeth Gardea

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