by Rodrigo Pérez Ortega
Science, June 30, 2020
The most biodiverse place on Earth is an oasis in the middle of the desert
When the NASA came knocking on ecologist Valeria Souza’s door in 1999 asking her to join an astrobiology project in the middle of the Chihuahuan desert, she never imagined it would be the start of a life journey involving living fossils, evolution, extraterrestrial life and billionaires, with pristine lagoons at the center of it all.
The Cuatro Ciénegas (Four Marshes) basin is a rare oasis in the state of Coahuila, Mexico. Surrounded by barren mountains, its unique geochemical features—including very low phosphorous levels and plenty of sulphur and magnesium—make this wetland arguably the most biodiverse place in the planet. The level of endemism in this place, which is a system of springs, streams and turquoise-blue lagoons, has been compared to that of the Galapagos Islands. But it also holds important clues about the Earth’s past. In 2006, Souza and her collaborators (including her husband) established in a PNAS paper that 50% of the group of microbes they identified were most closely related to marine groups, even though Cuatro Ciénegas has not been in contact with the ocean for tens of millions of years. In fact, Cuatro Ciénegas is one of the rare sites where live stromatolites, a bacterial form of life that once dominated the oceans, can still be found. Thus, the basin has served as a model to study early life, evolution and diversification, since the conditions are very similar to the ancient seas of the Precambrian. Because of the low-nutrient conditions of the area, this also makes it a very important astrobiological study site, as they are similar to those on Mars. (Besides microbes, other live forms are also endemic, including fish and turtles.)
However, the days of Cuatro Ciénegas have been numbered since the 1970s, when a canal was constructed to drain its waters to use it for agriculture. “In the last 50 years, we have lost 95%” of the wetland, Souza says. Many of the stromatolites, or “living fossils,” have disappeared. At the time, very few people knew about the scientific importance of this place, but Souza has now made it her life mission to save the wetland to preserve this biodiversity hotspot, while racing to get as much data as she can before the last pools dry up. She has fought corrupt governments, confronted a giant dairy company (Grupo LALA, which was using the water for the cows and are now on her side), and convinced Mexican billionaire Carlos Slim to invest in her research there. “It has been a very complicated, long and difficult process,” she says. “But at the same time, very fortunate and enriching.”
In 2018, Souza and her team described a site in Cuatro Ciénegas as model for a “lost word.” The extreme nutrient imbalance in El Churince lagoon there favored the survival of ancestral microbes, which persisted due to environmental stability and low extinction rates, generating a diverse and unique bacterial community. After sampling about 1 km2, researchers identified 5167 species representing at least two-third of all known major groups of bacteria. When researchers analyzed the 2500 genomes of the Bacillus bacteria they found, their results increased the number of previously known species in the group by 21%. Right after they finished the study (thanks to funding from Slim), El Churince lagoon dried because of water overexploitation. It survived millions of years, Souza says, but it couldn’t survive the last 50 years of human intervention.
But not everything is lost. Souza and her team have formed alliances and have involved local high school students to protect the site and contribute to research. And in March, she and her team will travel to Cuatro Ciénegas to witness the long-awaited closure of the canal that has drained the wetland. With this last victory, she hopes the wetland will start a restoration phase. Moreover, an additional purpose of the trip is to study Asgard archaeas in a new site dubbed Archean Domes, as research from last year confirmed that this is the site with most diversity of Archaea.
For her work, Souza, who is a professor of the Ecology Institute at the National Autonomous University of Mexico (UNAM), was inducted last year into the American Academy of Arts and Sciences. She is the first Mexican woman to receive this honor.
After a pre-interview with Valeria, she has invited me to come with her and her team to Cuatro Ciénegas from March 18-23. There will be four teams on this trip. Her team from UNAM, a team from Cinvestav Irapuato, a team from the Autonomous University of Nuevo León, and a visiting team from the Weizmann Institute of Science in Israel. The plan is to witness the closure of the canal, take sediment samples of the pools and soils samples of the region, and take samples of Asgard archaeas. They will also do educational workshops for the local high school.
For this feature story, I would like to tell the story of research at Cuatro Ciénegas, but also of Souza and the rest of the Mexican scientists who have taken the lead on preserving this place. I would also speak to Souza’s collaborators at Arizona State University and University of Minnesota, Saint Paul, as well as critics of her (if any) to get a balanced view.
Although Cuatro Ciénegas is not new in the Mexican media, I could only find two old pieces on it in international media: here and here. Moreover, I don’t think anyone has told the story in details of why this place is so important, they just say it’s very biodiverse. Moreover, I haven’t seen any stories that tell in full the details of Slim’s funding and how she convinced one of the most important dairy companies in the country to side with her.
Regarding budget, a roundtrip to Monterrey (the closest city with international airport) is about $350-$400 on those dates (from Washington D.C), and accommodation is about $32-$64 per night. Valeria and her team would pick me up in the nearby city of Saltillo, Coahulia, and take me to Cuatro Ciénegas in their cars. Food is also very cheap there.