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Accueil du site → Doctorat → États-Unis → 1989 → Temporal and spatial variability of soil moisture on the Jornada Range in southern New Mexico

New Mexico State University (1989)

Temporal and spatial variability of soil moisture on the Jornada Range in southern New Mexico

Nash, Maliha Saddiq Baqir

Titre : Temporal and spatial variability of soil moisture on the Jornada Range in southern New Mexico

Auteur : Nash, Maliha Saddiq Baqir

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 1989

This Dissertation consists of three parts. The main part (parts 1 and 2) deals with temporal and spatial variability of soil moisture along a 2730 m transect in southern New Mexico. Experiments were also conducted on solute transport through columns. The results of the latter experiments are presented in part 3. In part 1, soil water content and rainfall were measured bi-weekly at 30 m intervals along the transect. Time series techniques (autocorrelations and crosscorrelations) were used to examine the relationships between the water content and rainfall, and to compare the relationship of the overall average (the entire transect) soil moisture content with that of individual transect segments. Water content showed a significant correlation with rainfall with time lags between 6 and 10 weeks. The response time to rainfall was shorter in the surface soil than at the deeper depths. Wetting of dry soil was different for the entire transect as compared to individual transect segments. This difference is due to differences in soil texture along the transect, resulting in antecedent water content. In Part 2, soil moisture and vegetative cover (ephemeral, perennial forb and perennial grass) measured at 30 m intervals along the same transect were compared using kriging and cokriging. The average kriging and cokriging variances and the mean sum of squares (SSQ) were used to compare the two methods. Based on SSQ comparisons, cokriging is the best method for estimation of spring ephemeral cover (for observations from all stations) and for perennial spring grass cover (for observations from alternate stations). In part 3, the classical convection-dispersion equation was used to describe tritium and chloride movement through short soil columns. R values did not change for tritium when a model based on mobile-immobile water regions was used. This implies that all water in the soil column participated equally in tritium transport. Chromium transport was best described using a two-type sites adsorption model with a sink-term (irreversible reaction). A model based on two site sorption was used to describe boron movement in soil. For this soil Cr moved as fast as the water, while boron was considerably retarded.

Mots clés : Agronomy, Statistics, Hydrology, Pure sciences, Earth sciences, Biological sciences Temporal variability

Accès au document : Proquest Dissertations & Theses

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