Studying water quality in Colorado River Delta's Cienega de Santa Clara

A University of Arizona researcher is coordinating a project to monitor water quality in the largest wetland in the Colorado River Delta, the Cienega de Santa Clara in Mexico. The effort will evaluate how operation of the Yuma Desalting Plant (YDP) might affect the cienega.

Researchers will start gathering baseline information in August. The YDP is scheduled to conduct a 3-month trial run at 10 percent of its full capacity during the spring of 2007. The scientists will also collect water quality data during and after the YDP's trial run.

The Central Arizona Project (CAP) is funding the scientific monitoring effort.

"It's a critical first step in a long-term, bi-national effort to systematically evaluate how variation in water quantity and quality affects the delta's ecosystems," said the project's principal investigator Karl W. Flessa, a professor of geosciences at The University of Arizona in Tucson.

The Cienega de Santa Clara is an important stopover for birds that migrate along the Pacific Flyway and provides habitat and feeding grounds for an estimated 200,000 shorebirds, ducks and geese. It is also home to federally listed threatened and endangered species including the Yuma Clapper Rail (Rallus longirostris yumanensis), the Southwest Willow Flycatcher (Empidonax traillii extimus) and a species of desert pupfish, Cyprinodon macularius.

The cienega is also the basis of a growing ecotourism industry for nearby communities in Mexico.

"This project is a great example of how cross-border cooperation among federal agencies, state agencies, environmental groups and academic institutions can address critical problems in the use of water resources," Flessa said.

Jaqueline García-Hernández, a research scientist at Sonora's Research Center for Food and Development (Centro de Investigación en Alimentación y Desarrollo) in Guaymas, Mexico, is the project's director. She and Osvel Hinojosa-Huerta, a UA doctoral candidate and conservation director at Pronatura Noroeste-Sonora in San Luis Río Colorado, and their colleagues will conduct the field and laboratory studies. García-Hernández studied water quality in the cienega and elsewhere on the Colorado Delta as part of her doctoral research at the UA.

Most of the water that flows into the Cienega de Santa Clara is from Arizona's Wellton-Mohawk Irrigation and Drainage District. The water, which is primarily agricultural return flow, is too salty to count toward the United States' treaty obligation to provide Colorado River water to Mexico. The water has been directed into the cienega since the 1970s. Now about 100,000 acre-feet (32.6 billion gallons) of brackish water flows into the cienega each year.

The U.S. Bureau of Reclamation's YDP, completed in 1992, was built to desalinate the water that now supports the Cienega de Santa Clara. But the high streamflows on the Colorado River at that time were sufficient to provide the low-salinity water the United States is required to provide Mexican farms and cities. Therefore, the YDP has never gone into regular operation.

The current drought has renewed interest in running the plant, but its full-scale operation would mean that the cienega would get less water and the water would be much saltier, Flessa said. Such water might harm many of the plants and animals that live there. Environmental groups have opposed running the de-salting plant because of the potential impact on the cienega.

In 2005 Sid Wilson, general manager of the Central Arizona Project, led a working group of key people from water agencies and environmental groups to issue a report, "Balancing Water Needs on the Lower Colorado River," ( that identified ways to meet the needs of water users in the United States and Mexico without harming the cienega. The group suggested alternate sources of water for the YDP to use and also alternatives to desalinization.

The report called for starting a monitoring program for the cienega. The CAP has provided $80,000 for the new monitoring program.

"CAP's support for this project is outstanding. It marks the beginning of the end of one of the most bitter water wars on the Lower Colorado," said working group member Jennifer Pitt of Environmental Defense.

Water samples will be taken every month for the next year from 17 locations within the cienega. The program will test the water's salinity, dissolved oxygen, nutrients, selenium concentration and other characteristics and will evaluate whether the trial run of the YDP has affected water quality.

"Monitoring during the next year will provide long-needed baseline information and increase our understanding of how hydrologic variation affects environmental quality in this critical wetland," said Flessa, director of the National Science Foundation-supported Research Coordination Network for the Colorado River Delta.


Contact information:

University of Arizona:
Karl W. Flessa
[email protected]

Central Arizona Project Media Contact:
Robert Barrett
[email protected]

Bureau of Reclamation:
Jim Cherry, 928-343-8155
[email protected]

Environmental Defense:
Jennifer Pitt, 303-447-7209
[email protected]

Related Web sites:

Colorado River Delta Research Coordination Network

Central Arizona Project

Balancing Water Needs on the Lower Colorado River:
Recommendations of the Yuma Desalting Plant/Cienega de Santa Clara Workgroup

Yuma Desalting Plant

Environmental Defense

Last reviewed: By John M. Grohol, Psy.D. on 30 Apr 2016
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