Threatened Mexican oasis loses its main researcher and protector — will it survive?

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On a warm day in March, ecologist Valeria Souza went into a temazcal, or sweat lodge, in Texcoco, Mexico, to pray for the wetlands that she had been studying in the Chihuahuan Desert for the past quarter of a century. She had been performing this shamanic ceremony for years, asking for guidance to help save the scientifically treasured basin in the northern reaches of the country — known as Cuatro Ciénegas — from human exploitation. But this time was different.

Souza, the region’s lead scientist, based at the National Autonomous University of Mexico in Mexico City, instead asked for permission to step away and forgiveness that she couldn’t do more. Despite the fight she’d put up, farmers and other local residents have been slowly draining water from the area for their crops and other sustenance. This has led to many of the basin’s pools drying up, turtles and plants dying, and prized microbes receding into the ground beyond researchers’ grasp. With climate change pushing the landscape’s temperatures ever higher, it has been an uphill struggle.

Souza loves Cuatro Ciénegas. Researchers think that the isolated landscape has preserved microorganisms for hundreds of millions of years. “It’s a unique window into the past,” she says. But she is also tired, and says that it’s time to leave the task of protecting the basin to a new generation of scientists and advocates.

A lost world

Cuatro Ciénegas, which translates to ‘four marshes’, has long fascinated scientists. Although its name was inspired by springs located at the four cardinal points shaping the valley, in total, it contains more than 300 blue-green pools, or pozas, filled with microbes, bacterial mats and ancient microbial reefs called stromatolites. “It’s perhaps the most diverse place on the planet in terms of bacteria and archaea,” Souza says.

Valeria Souza, during a visit to Cuatro Ciénegas.Credit: Esteban Gonzalez de Leon

The wetland is fed by “an ancient sea” beneath the nearby Sierra de San Marcos y Pinos mountain, Souza adds. Rain on the mountain feeds the aquifer, which is heated by magma deep underground. The water then seeps upward, through ancient marine sediments, to form the pools.

The region’s stromatolites have especially intrigued scientists. In other parts of the world, researchers usually come upon stromatolites as fossils — dried-out layers of ancient cyanobacteria containing trapped sedimentary grains. But those in Cuatro Ciénegas are alive, allowing scientists to study what early life on Earth must have been like. One way they do this is by extracting stromatolite DNA and analysing how it might have evolved.

Drawn to the area in 1998, researchers funded by NASA’s Astrobiology Institute in Mountain View, California, went there to study the origins of life — with an eye towards understanding whether life could have once existed on Mars’s arid surface. James Elser, a limnologist who was one of the lead scientists on the project and who was at Arizona State University in Tempe, invited Souza to collaborate.

Emptied oasis

Souza confesses that the fight to save the place has been like a rock on her back.

Because it is one of the most abundant sources of water in the Chihuahuan Desert, Cuatro Ciénegas has been tapped extensively by local residents. Three main canal systems — La Becerra, Santa Tecla and Saca Salada — siphon water from the wetlands, especially to grow alfalfa (Medicago sativa), a crop mainly used to feed cows.

To halt this drainage, Souza brought in Mexican business magnate Carlos Slim, who partnered with the global wildlife charity WWF in 2009 to buy the land around the region’s largest lagoon, El Churince, and make it a protected area. She also successfully lobbied the dairy company Grupo LaLa, based in Gómez Palacio, to stop buying alfalfa from the region. But demand for water continues to soar, and the wetlands have steadily dried up.

This set of time-lapse aerial images shows El Churince, once the largest lagoon in Cuatro Ciénegas, dry up and disappear (images run from 1997 to 2022).Credit: Landsat data courtesy of the U.S. Geological Survey

By 2017, El Churince — which held the vast majority of fish species found in Cuatro Ciénegas and housed more than 5,000 species of bacteria, most of them only found in the region — was gone. Souza says that, after seeing the “graveyard of turtles and fishes” left behind, she mourned for years.

Others have tried to protect the region. For instance, in 2000, the civil association Pronatura Noreste in Monterrey acquired the Pozas Azules ranch, whose roughly 2,700 hectares hold 100 of Cuatro Ciénegas’ pools. But the organization has similarly struggled to make headway. The land is protected, but the aquifer beneath it is not, says the association’s director, Rosario Alvarez.

Souza would like to see Mexico’s National Water Commission (Conagua) take more stringent steps to protect the aquifer. The agency doesn’t keep a record of all the water that’s extracted from it, or the permissions for its use. This leads to over-extraction, which is collapsing the wetland, she says. “There is no inventory, and it’s urgent that [Conagua keep one] because the system cannot last five more years,” Souza adds.

Conagua did not respond to Nature’s requests for comment.

Saving an ancient world

Souza’s one hope is the generation of scientists and advocates she trained.

When she became interested in Cuatro Ciénegas, she spent time educating children from the local school, CBTA 22, as well as the surrounding community, about the importance of preserving the wetland. Among the people she taught is Héctor Arocha, now a biotechnologist who is taking over research in the basin. Arocha works for 2040 Plan, a foundation in Cuatro Ciénegas that seeks to support the development of the community over the next 25 years.

As part of that effort, on 4 April, Arocha opened Genesis 4C, the first scientific museum in the region, with the mission of creating a culture of conservation. “We gathered all the research that has been done in the valley in collaboration with Valeria and the whole team of researchers who have come over the years,” Arocha says. The museum has a research centre and plans to continue microbial-ecology projects on the origins of life, as well as to find uses for the wetland’s microorganisms in agriculture and medicine.

Souza also sees ecotourism efforts in the area as promising. “Hoteliers and non-governmental organizations own the largest areas of Cuatro Ciénegas,” she says. One of the hotels, the María Elena, is donating to the 2040 Plan. There’s also an ecotourism park, called Las Playitas, that educates visitors about the marshes and donates money to the foundation.

It’s hard to know whether the pools of Cuatro Ciénegas will survive, but Souza takes solace in the longevity of the bacteria that she loves. “Time is very relative” to the microbes living under the mountain, she says. The water in the pools might completely dry up, but the microorganisms are capable of patiently waiting millions of years underground before rising back up to the surface if the aquifer ever refills. Humans might never see that — “we will be extinct by then”, she predicts — but the microbes could endure.

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