HR: 1340h
AN: H43D-0517    [Abstracts]
TI: GroundwaterGeochemistry,SeasonalChangesandControlsonEolianMorphology.WhiteSandsNationalMonument,NewMexi co,TX
AU: * Rose, J M
EM: jmrose@utep.edu
AF: University of Texas at El Paso, 500 W. University, El Paso, TX 79965 United States
AU: Langford, R P
EM: langford@utep.edu
AF: University of Texas at El Paso, 500 W. University, El Paso, TX 79965 United States
AU: Cueto, M J
EM: mjcueto@utep.edu
AF: University of Texas at El Paso, 500 W. University, El Paso, TX 79965 United States
AB: The White Sands of New Mexico is composed of transverse, barchan and parabolic dunes formed of gypsum sand. Transverse dunes pass downwind into barchans and then vegetated parabolic dunes. This study focuses on the transition from barchan dunes that migrate rapidly (12 m/year) through an unvegetated landscape, to isolated parabolic dunes migrating at 1 to 2 m/year through vegetated, stabilized dunes and sand sheets. One theory is the vegetated parabolic dunes form where enough sand has been deposited above the permanent saline water table to allow the formation of a fresh water lens. Conversely, where there is enough vegetation, due to the permanent and highly saline groundwater table, the sand blows away as barchan dunes, deflating the dune field. In a 5 km long swath through the dunes, six sampling sites were established: two barchan, two parabolic and two in the transition zone between the two dune types. Groundwater as well as soil samples were collected to measure the seasonal variations on water salinity and of sand movement in the dune field. The water table is less than 1.5 m at all sites. During successive sampling during the first half of 2005, at the barchan sites, the water is three times more saline than the parabolic sites at (20,000 g/ml vs. 3,000-8000 g/ml). Sampling each two months from early December through June suggests the influx of fresh water into the basin has caused a salinity decrease in the soil water in both the transition and parabolic sites during the spring and summer from about 2,000-3,000 mg/L to about 1,000 mg/L). March results show an overall decrease in salinity readings although in May the results are more varied, showing some sites high and some showing low salinity readings but mostly ranging about 1,000 mg/L. The parabolic dunes specifically show an increase, in salinity from 1,000 mg/L in December to 8,000 mg/L in May. During the winter, thin zones of high salinity, or spikes, are found between 40 and 80 cm deep in the soil column in the parabolic dune area. These may correlate with very fine grained layers (mean 5 microns) in the soil. In the Transition sites, salinity decreases from December to May but hovers around 10,000 mg/L. The Barchan sites have relatively low salinity readings above the groundwater, whereas the groundwater is very saline. The values at the barchans sites remained relatively the same throughout the six months at around 20,000 mg/L. TDS (total dissolved solids) decreases from 7 g/L in the barchan to 2g/L in the parabolic dunes. In the barchan area, the amount of DO (dissolved oxygen) is also greater. It is presumed the vegetation and the associated ecology withdraw soil water, creating higher salinities in the soil column. These layers may have formed through precipitation from groundwater or through soil alteration of the eolian sand. The dramatic changes in groundwater salinity suggest dune fields can be shaped by dynamic feedback between eolian dynamics, vegetation and groundwater chemistry.
DE: 1051 Sedimentary geochemistry
DE: 1806 Chemistry of fresh water
DE: 1809 Desertification
DE: 1829 Groundwater hydrology
DE: 1852 Plant uptake
SC: Hydrology [H]
MN: Fall Meeting 2005