“The treatment wetland has been one of the great success stories in the Colorado River Delta region.”Osvel Hinojosa, National Geographic Explorer/Director del Programa de Agua y Humedales, Pronatura Noroeste

It has turned desert into oasis, a noxious pollutant into a source of new life. Our Colorado River Delta program is filled with amazing outcomes, and the Las Arenitas treatment wetland is a truly remarkable story of reclamation and renewal.

Flying over this area of the Delta, just south of the U.S./Mexico border and past Mexicali, the capital of Baja California, you would never guess that you are looking at what used to be one of North America’s most important wetlands. Before upstream dams and diversions for farms and cities in the U.S. and Mexico slowed the Colorado River to a trickle, the river fed almost 2 million acres of fertile habitat for birds, fish, and other wildlife. Now, you see a panorama of tan, the color of dry. The dusty nothingness is so absolute that it’s no wonder most people had until recently given up the Delta for dead.

But soon you’ll see another sight, our vision of what is possible in this desiccated landscape. Next to a municipal wastewater treatment plant in the middle of this desert appears an unlikely expanse of water, vegetation, birds, and even tourists—250 acres of life.

Raising a Stink

All of this bounty started as waste. In 2007, to help deal with wastewater from its growing metropolitan region, the Mexicali state water authority, through the Comision Estatal de Servicios Publicos de Mexicali (CESPM), built the Las Arenitas Wastewater Treatment Plant. Soon after it began operation, however, it was apparent that the plant was already over capacity. Wastewater that was not treated up to standards suitable for human contact flowed into the Hardy River, a tributary of the Colorado River that is popular for hunting, fishing, boating, and swimming. Owners of homes and vacation camps along the river objected not only to the smell, but also to the risks to their health, their property values, and their tourist and recreation businesses.

Amid this mess, Francisco Zamora Arroyo, director of our Colorado River Delta Legacy Program, saw both a solution and an opportunity.  “In 2008, we approached CESPM with a plan to create a wetland next to the treatment plant that would provide additional treatment capacity, while also enhancing the river system and the local economy,” he says.

The idea was the wetland would acts as a biofilter, removing sediment and pollutants from the partially treated wastewater. Natural chemical processes and microorganisms living in the wetland’s vegetation would break down organic materials over time and improve the water quality.

We began construction in 2009. The treatment wetland is now 70 percent completed—and it’s working. The wetland is helping the state water authority and the city of Mexicali meet water quality standards at a lower cost than expanding the plant itself, and the improved conditions of the Hardy River are boosting property values and tourism and recreation businesses in the area.

But that’s just the start. The Delta is a critical stopover point for birds traveling along “Pacific Flyway,” the major north-south migration route that extends from Alaska to Patagonia at the southern tip of Argentina. The wetland has created new habitat for these birds, and provides a unique opportunity for people living in Mexicali to experience a wetland 20 minutes outside the city. For now, the recreation area includes walking trails and a small visitor center, but the state has proposed creating a more extensive municipal park in the future.

Furthermore, thanks to a forward-looking agreement that Sonoran Institute and our partner Pronatura Noroeste reached with the state government and CESPM, the wetland’s benefits extend far beyond the treatment area itself. We asked that 30 percent of the treated “effluent” (wastewater) be dedicated to the Hardy River. This ensures that, at current capacity, some 8,000 acre-feet of water flows into the Hardy River, and eventually into the Colorado River, every year for the next 20 years. The dedicated amount increases as more wastewater is treated at Las Arenitas, and will probably ultimately rise to about 12,000 acre-feet. The agreement represents one of the only instances in Mexico that effluent has been dedicated to environmental purposes. (story continues below sideshow)


Flocking Back

“The treatment wetland has been one of the great success stories,” says Osvel Hinojosa of Pronatura Noroeste, one of our longtime partners in the Delta and the organization that has been monitoring the bird population at Las Arenitas from the beginning of the project. “There’s been a very fast restoration response.”

In 2009, according to Osvel, the first count of birds in the area yielded about eight species and fewer than 100 total birds. Six years later, 160 different bird species are present, with a maximum bird count of 18,000 birds.

“The coolest part is that the wetland is providing breeding grounds for Yuma Clapper Rail and Virginia Rail,” Osvel says. “These are very rare birds that are endangered, so it’s really exciting that they are using the site for breeding.”

Of the many successes from the project, Osvel sees a shift in mindset as the most significant.

“The landscape itself is beautiful and very inspiring, but for me what is really important is the change in perspective from the water agencies,” he says. “Before this project, it was not conceivable that the agencies would invest so much in an environment project, in raising habitat, restoring wetland. And now they are very excited about Las Arenitas. The last three governments of Baja California are really excited about restoring wetland. For me, that change is the real importance of Las Arenitas. It has brought the topic of restoration to a very high level. “

State water officials agree: “The artificial treatment wetland was a creative solution that has allowed us to meet water quality standards with the additional benefit of creating a thriving wetland habitat. We acknowledge Sonoran Institute’s dedicated and pragmatic approach to restoring the Delta and helping improve quality of life in the region.  We are very happy with the success of the treatment wetland and look forward to continuing to partner with them in the future.”

Working together, the partners have developed the know-how for building a treatment wetland and are already looking to create another, smaller wetland, as growing treatment demands are quickly outpacing capacity.

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