Date of Award

1-1-2009

Document Type

Dissertation

Degree Name

Ph.D.

Organizational Unit

College of Natual Science and Mathematics

First Advisor

Anna A. Sher, Ph.D.

Second Advisor

Kenneth D. Lair

Third Advisor

Robert Sanford

Fourth Advisor

J. Michael Daniels

Keywords

Groundwater, Revegetation, Salinity, Saltcedar, Soil, Tamarix

Abstract

Tamarix spp. (a.k.a. saltcedar, tamarisk) invasion is considered a major ecological threat at both national and global levels, with supposed impacts on soil and water chemistry. One of the most often cited mechanisms of ecosystem change by Tamarix is through its ability to deposit salty exudates and salt-rich leaf litter. The degree to which Tamarix relates to elevated soil and groundwater salinity, however, has not been adequately quantified, especially in the context of environmental factors that may also influence salinity. If Tamarix does elevate localized salinity by means of uptake, concentration and exudation by plant tissues, then we might expect that the magnitude of its impact would be influenced by stand features such as density and age. Therefore, we analyzed soil and groundwater salinity associated with Tamarix stands across a gradient of densities and aboveground ages along an arid reach of the Middle Rio Grande in Central New Mexico. Stands were sampled both in areas exposed to and deprived of flooding to account for potential hydrologic impacts on soil and groundwater chemistry. Paired soil samples were collected underneath Tamarix canopies and in adjacent open areas to compare solute concentrations associated with Tamarix cover to those in soils exposed to greater rates of surface evaporation. Results indicate that flooding may be the most important factor for assessing floodplain salinity as the presence of this flushing mechanism was related to the lowest salt levels. Surface soil salinity was observed to increase with greater Tamarix stem diameter (a predictor of age) in areas deprived of flooding; however a hyperbolic pattern where salt level is highest under intermediate-aged growth and lowest underneath younger and older canopies seems to better explain the variability associated with salt level change by age. Tamarix density was not observed to influence soil salinity, but higher densities were associated with elevated groundwater salinity in flood-suppressed areas. Soils under Tamarix canopies had lower surface soil salinity than open areas deprived of flooding suggesting that surface evaporation may contribute more to surface soil salinity than Tamarix or may exacerbate contributions by leaf exudates. This research provides a unique opportunity to quantify the degree to which an invasive species can alter its environment. Results can be used to guide management decisions related to native species revegetation of Tamarix-invaded areas.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Michelle Kelly Ohrtman

Provenance

Received from ProQuest

File Format

application/pdf

Language

en

File Size

188 p.

Discipline

Ecology

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