Groundwater use is of fundamental importance to meet rapidly expanding urban,
industrial, and agricultural water requirements, particularly in semiarid zones. To
quantify the current rate of groundwater recharge is thus a prerequisite for efficient and
sustainable groundwater resource management in these dry areas, where such resources
are often the key to economic development. Increased groundwater recharge has been
documented where native vegetation or forest/shrub land was converted to grassland or
pasture, or where the land was cleared for agricultural purposes. The basic argument for
increased recharge is that evapotranspiration, primarily interception and transpiration, is
higher in shrublands than grasslands.
Chloride mass balance (CMB) has been used to estimate ancient recharge, but
recharge from recent land-use change has also been documented, specifically where
vegetation has been altered and deep-rooted species replaced with shallow-rooted
grasses. Chloride concentrations are inversely related to recharge rates: low Clconcentrations
indicate high recharge rates as Cl- is leached from the system; high Cl concentrations indicate low recharge rates since Cl- accumulates as a result of
evapotranspiration.
The objectives were (1) to assess the hypothesis that removal of woody-shrub
vegetation and replacement with grasses increases deep drainage, (2) to quantify the
amount of deep drainage after land-use change, and (3) to provide science-based data for
a better understanding of changing land-use impacts on deep drainage. Eight soils from
five locations in the Central Rolling Red Plains near Abilene and Sweetwater were
sampled. Each location consisted of a pair of similar soils with contrasting vegetative
cover: shrubland and grassland. At each site three to five soil cores were taken as deep as
possible and samples were taken by horizon, but horizons were split when their
thickness exceeded 0.25 m.
Soil Cl- profiles under shrubland at three sites showed that virtually no water
escapes beyond the root zone. High Cl- concentrations and inventories reflect soil
moisture fluxes that approached 0 mm yr-1 with depth. Evapotranspiration may be
largely responsible for Cl- enrichment in those profiles. Surprisingly, soil moisture flux
past 200 cm under juniper woodlands was the highest with 2.6 mm yr-1.
Evapotranspirative Cl- enrichment in the upper 300 cm was not observed and may
suggest a different water uptake mechanism for this plant community.
Soil Cl- profiles showed increased recharge rates under grassland vegetation
ecosystem. Estimated deep drainage past 200 cm of 0.1 to 1.3 mm yr-1 was observed.
Low Cl- concentrations and inventories suggest a leaching environment that may be in
response to changes in land use/land cover.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7603 |
| Date | 2009 December 1900 |
| Creators | Navarrete Ganchozo, Ronald J. |
| Contributors | Hallmark, Charles T. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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