EL PASO — Increasing salinity levels in the Rio Grande above Amistad Dam may threaten the amount of water that can be used for drinking or crop irrigation, according to a new study from the Texas Water Resources Institute and the Texas Agricultural Experiment Station.
The report, “Flow, Salts, and Trace Elements in the Rio Grande: A Review,” was co-authored by Drs. Seiichi Miyamoto and Lloyd Fenn of the Texas A&M University Agricultural Research Center at El Paso, and Dr. Dariusz Swietlik of the Texas A&M University-Kingsville Citrus Research Center at Weslaco.
Miyamoto said salinity is the major factor that limits how water can be used in the region. The highest salinity levels in the Rio Grande occur from Fort Quitman to Presidio (2,000 to 5,000 milligrams per liter) and where the Pecos River enters the Rio Grande (2,000 to 4,000 milligrams per liter).
Salinity levels above Amistad Dam have steadily increased since the 1950s, and at some sites are higher than U.S. Environmental Protection Agency limits for drinking water and guidelines for the water quality needed to irrigate crops. Salinity problems in Amistad Reservoir also are getting worse, according to the study.
“The continuing increase in salinity levels in Amistad Reservoir is of special concern,” Miyamoto said, “because it will further limit how water can be used in this arid region. The standard way of lowering high salinity levels is by providing increased freshwater flows, but unfortunately that’s not a viable solution here because water supplies and surface water runoff are limited.”
He said that alternative solutions to reduce salinity levels may include minimizing flows of saline water into the river. This could be done by developing brine diversion dams or to reuse saline water to irrigate salt-tolerant grasses and other crops.
Miyamoto said that deterioration of water quality could have negative implications for high value agricultural production in the Middle and Lower Rio Grande. For example, many crops that are now grown in the region — such as chile and green peppers, onions, pecans, citrus, and peaches — can thrive when salinity levels are moderate, but production could decrease if too much salinity occurs.
The report also includes information on the flow of the Rio Grande and its tributaries, current levels of salts and trace elements, and compares existing contaminant levels in the river to water quality standards.
Miyamoto said that a significant result of the report is an increased realization of how little is known about the Rio Grande and how much research still needs to be done.
“This report provides an overview of how water quality in the Rio Grande watershed has changed over the past 45 years and what some of the implications of those water quality changes may be,” Miyamoto said. “Because more salts and higher levels of sodium are building up in the river, there may be an increased likelihood that soils will deteriorate and will be less able to support high value crop production.”
The report recommends that more studies are needed to determine how to manage irrigation return flows, how to control salinity and limit salt loads, how to manage sodium inputs, and trace element monitoring.
The report (TR-169) is available free from TWRI by calling (979) 845-1851.