SOURCES, TYPES, STORAGE, AND RELEASE OF SALTS IN THE SOIL-WATER SYSTEM OF THE RIO GRANDE, TEXAS

Salts are the most frequent contaminant that limits full utilization of the Rio Grande (RG) in Texas. This study investigated the sources and type of salts of the Rio Grande between El Paso and Del Rio, Texas. The study used data from high-resolution spectroradiometer, GER 3700, with recent and historical hydrochemicaland climatic data obtained from Texas New Mexico Water Commission (TNWC) and the U.S International Boundary and Water Commission (US IBWC); microscopic and other geochemical techniques were also used to achieve the mentioned objectives. The study found that salinity began to increase in the Rio Grande due to salt flushing from the Pecos and the middle Rio Grande, and the more recent increase (after 1995) was caused by drought in the Rio Conchos Basin in Mexico. More basic reasons include increased uses of the water resources in the middle Rio Grande, irrigation return flow, and salt pick-up in the Pecos Basin and due to evapo-transpiration from salt cedars, which have spread over the Pecos, as well as the middle Rio Grande. The study found that the chemistry of the water in the Rio Grande was dominated by sodium, chloride, calcium and bicarbonate ions. Four different types of salt crusts exist in the Rio Grande were reported. Those included: a) white puffy crusts and were identified as hydrated calcium sulfate b) hard white pans and identified as sodium sulfate, c) thin transparent crusts and were identified as sodium chloride d) transparent crystallized crusts with brown and silt like color, and were identified as sodium chloride mixed with silt and clay. The study also classified the corridor types of selected riparian zones of the middle Rio Grande in the vicinity of El Paso, Texas that is responsible for salt storage and release processes of RG, as the collected data indicated. Those types were: a) barrier consist of clayey type of soil without void of vegetation, and sodic soil, 2) conduit of connected sandy soils patches, soil with good drainage and free from sodium salts, soil with high relative gradient, and 3) source-type of corridor which consist of salt crusts on compacted soils with thickness of 3 to 5 cm.