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Scientists and farmers restore Aztec-era floating farms that house axolotls

  • In 1987, UNESCO declared the Xochimilco wetland area in southern Mexico City a World Heritage Site, recognizing in particular its chinampas, an ancient agricultural system in use since the time of the Aztecs.
  • In the past few decades, Xochimilco’s levels of production and of biodiversity have shifted: people have changed the purpose of many chinampas, and the population of axolotl salamanders, an iconic species endemic to the area, has decreased drastically.
  • Scientists from the Ecological Restoration Laboratory at the National Autonomous University of Mexico and farmers from the area are promoting a comprehensive restoration program to conserve this group of chinampas and all the living things that depend on it.

It was the 1980s, and before sunrise, Basilio Rodríguez was ready to work. He was still young, and he’d already helped to prepare the land for crops, gathered harvests, pulled weeds and took care of the plants. In late October, when he spent his nights cutting Aztec marigolds for the Day of the Dead, he would sleep on chinampas, or small artificial islands for developing agricultural systems. These were created by the Aztecs and are a large part of the identity of Xochimilco, a lake-filled area that has managed to survive in southern Mexico City.

It’s now a hot morning in September 2023. Rodríguez — slender, with an easy smile and soft voice — is 54 years old. It’s his day off from work, but he doesn’t spend it relaxing at home. Instead, he’s set out to work on his chinampa, a floating piece of land measuring less than a quarter hectare, or half an acre, on which crops can be cultivated. These include everything from epazote, a Mexican tea, to mint, parsley, radishes and onions to pumpkins, chamomile, rosemary and Aztec marigolds. The harvest depends on the season. Right now, this land, located in the Xochimilco wetlands, is plastered green with rows and rows of lettuce, ready to be cut and sold at market. Rodríguez plans to sow 10,000 additional lettuce plants in the space he’s prepared.

His chinampa, reachable only by canoe, is now unconventional in the area.

In the past, these pieces of land were only used to cultivate vegetables and leafy greens, as Aztec farmers did in the second decade of the 16th century. For several decades now, the purpose of chinampas has started to change: some are now soccer fields, restaurants, speakeasies, party rooms, sweat lodges, or domed steam baths made of adobe. Others have been abandoned. It’s a very different picture from 1987, when UNESCO granted World Heritage Site status to Lake Xochimilco and its chinampas for their role as a unique agricultural production system.

When he was a child, Basilio Rodríguez recalls “a huge number” of chinampas being used for agriculture.

“I knew so many farmers and they didn’t sow small [amounts] like I did; they planted between 7 and 8 hectares [17-20 acres],” Rodríguez says as he leans on his garden hoe, his hands caked with black dirt.

As the years went by, the landscape changed and caused concern.

In 2018, data from the United Nations’ Food and Agriculture Organization (FAO) revealed how much Xochimilco and the four other areas of Mexico City with chinampas — San Gregorio Atlapulco, San Luis Tlaxialtemalco, San Pedro Tláhuac and San Andrés Mixquic — had changed. Of 20,922 chinampas, only 17% were still being cultivated in an open-air environment or with greenhouses, shade nets or macro tunnels. The vast majority had been abandoned.

Yet despite its transformation, Xochimilco maintains its status as a World Heritage Site.

Basilio Rodríguez is known as the best fisher in the area, but that’s not his only talent: he also grows vegetables and leafy greens. Image by Aminetth Sánchez.

By changing local agricultural practices, the transformation of the chinampas also drove changes in the region’s biodiversity. This is because, in this area filled with lakes, everything is linked like a large chain, according to Carlos Sumano, a member of the Ecological Restoration Laboratory within the Institute of Biology at the National Autonomous University of Mexico (UNAM). If chinamperos, the people who work the chinampas, are in danger of disappearing, then so is the axolotl (Ambystoma mexicanum), the iconic species of Xochimilco.

For 15 years, researchers from the Ecological Restoration Laboratory and local farmers have worked to restore the area where the chinampas are. Their plan involves reducing the number of carp and tilapia (which are introduced species), promoting environmental monitoring, and creating “chinampa refuges” to reverse the transformation.

Giving a future to a species and an ecosystem

The axolotl is “an aquatic monster.” At least, that’s its name in the Nahuatl language: atl means “water,” and xólotl means “monster.” Its external gills, its smooth, scaleless skin, its crests, its fins, its ability to regenerate parts of its body, and its small eyes are part of one interpretation of the Fifth Sun myth, written by Bernardino de Sahagún, a Franciscan friar, in 1577. It said that in order to make the sun and the moon move in the sky, a god needed to be sacrificed; but one deity, Xólotl, Quetzalcoatl’s twin, tried to escape death by turning into a cornstalk, then into an agave plant, and, finally, into an axolotl. In the end, he was killed.

The axolotl is one of 16 species of salamanders in the genus Ambystoma that’s native to Mexico. The axolotl itself is found only in Xochimilco and the other chinampa areas around Mexico City; it’s listed domestically as endangered, and globally as critically endangered.

Imagen de un ajolote registrada en la laguna de Alchichica. Foto: José Alfredo Hernández.
An axolotl in Laguna de Alchichica. Image by José Alfredo Hernández.

When the Aztecs designed this area’s system of canals and wetlands, axolotls grew and reproduced successfully in these habitats. A 2015 study noted it was common to see axolotls moving around in the water or being used as a source of food in communities. After the fall of the Aztec Empire in 1521, these aquatic ecosystems began to deteriorate.

“The pace of deterioration was gradual and subtle until the middle of the 20th century,” the study noted. “At this time, axolotls seemed to be sufficiently numerous to support a fishery for local consumption. However, the rate of deterioration increased precipitously as Mexico City more than tripled in size between 1950 and 1975.”

The destruction of the area around the lakes has advanced quickly, and the causes behind it have only diversified. In addition to the growth of the urban area, other factors include the introduction of exotic species — particularly fish like carp and tilapia — in the 1970s; the application of agrochemicals in some chinampas; wastewater discharge from nearby homes; changes in land use; the quantity and quality of the available water; and the use of motorboats for transportation.

“A progressing trend started to be seen in the decrease in the number of axolotls per square kilometer in the Xochimilco area and, overall, in the remainder of the basin,” Sumano said.

The Ecological Restoration Laboratory at the Institute of Biology at UNAM has an ambitious goal: the long-term restoration of the chinampas in Xochimilco. This will be done by applying an intensive fishing program to reduce the number of carp and tilapia, with an environmental monitoring system and the rehabilitation of chinampas and secondary canals to create refuges to strengthen the conservation of the axolotl and other native species. Image by Aminetth Sánchez.

The density of axolotls dropped from 6,000 per square kilometer (15,500 per square mile) in 1998 to only 100/km2 (260/mi2) in 2008, according to the 2015 study. This represents a decrease of 98% in 10 years, and that decline has only continued.

Luis Zambrano González, director of the Ecological Restoration Laboratory at UNAM, led the most recent census of axolotls. In 2014, together with his team, he set out to count how many of the salamanders there were in the Xochimilco ecosystem. Sitting in a boat, with an axolotl expert in the front, the team shot a net into the canals to determine how many axolotls were in the area. They found less than 35/km2 (91/mi2). This is a drastic decrease that was confirmed by nearby residents, who say they fear that when the next census is conducted, there won’t even be 10/km2 (26/mi2). “Yes, yes, yes, that scenario is very possible,” Zambrano says.

To prevent this scenario from worsening, a team of researchers and farmers is working on a restoration project to create chinampa refuges.

Water: The focus of the rehabilitation efforts

Carlos Sumano bikes to his workplace, Cuemanco dock in Xochimilco, one of the points of departure for the area’s traditional trajineras, or wooden boats decorated with flowers and colored paper. As soon as he arrives, the 39-year-old takes a hat, puts on some rubber boots and steps into a canoe. Using his sense of balance, good rowing technique and a clear route, he gets to work managing the restoration project: resolving pending matters, talking with chinamperos, and visiting the refuges where the ongoing work to recover the axolotl population is taking place.

Carlos Sumano is the bridge between the chinamperos and the UNAM laboratory. Image by Aminetth Sánchez.

For the last 15 years, the Ecological Restoration Laboratory at UNAM’s Institute of Biology, coordinated by Zambrano, has had an ambitious goal: the long-term restoration of the chinampas in Xochimilco. This will be done by applying an intensive fishing program to reduce the number of carp and tilapia, with an environmental monitoring system and with the rehabilitation of chinampas and secondary canals, used for irrigation, to create refuges to strengthen the conservation of the axolotl and other native species.

“The first three or four years, we were dedicated to trying to understand the fundamental causes of why the axolotl was headed toward extinction,” Zambrano says. Later, in collaboration with people who own the chinampas, they finished developing the comprehensive plan. “The time spent, and the constant work with chinamperos, resulted in a robust plan. These are two things in restoration ecology which do not always work; people do restoration dynamics and leave. Then the locals say, ‘This doesn’t help me at all.’ What I’ve learned is that if one wants to do a restoration project, it has to be long term.”

What the laboratory wants is not only to have more axolotls, but also to restore their entire habitat. “We can have a billion axolotls in fish tanks. It’s nothing more than a matter of having the fish tanks; it is possible, and many [people] do this. But that is not useful,” Zambrano says. “If we wipe out the axolotl in Xochimilco and there are many in Germany, the species no longer exists, because the species is an evolutionary product of its interaction with its own ecosystem; it is a fundamental part. In another way, it is a combination of DNA that survives but is not a species as we know it, because it also modifies its habits, its behavior, its physiology. So restoring the species essentially involves restoring its habitat.”

The project addresses the crux of several problems, including the quantity and quality of the water, according to biologist Miguel Rivas, a member of the laboratory. “There was a negative feedback loop: bad harvests, little monetary income [for farmers], land abandonment, and so the quality of water and the biodiversity were dropping,” Rivas says in an interview at his lab a 30-minute drive from Xochimilco.

Improving the area’s water quality also increases the agricultural yields of the chinampas, protects the lives of native species — such as axolotls, mesa silverside fish (Menidia jordani) and acocile shrimp (Cambarellus montezumae) — and reduces the presence of exotic species. This positive cycle aims to counteract the negative loop that the researchers have identified.

Rivas adds that wetlands like Xochimilco are strategic ecosystems for mitigating the effects of climate change. This is primarily due to the important role they play in terms of carbon capture and storage. This is also because they act as shock absorbers for extreme changes in the climate, and even more so if they’re located in a city. “If at any moment the Xochimilco wetland were to disappear, it would immediately have several impacts, as if they were billiard balls: it would affect the temperature, flooding and carbon capture. It would change the environment much more,” Rivas says.

A restored ecosystem has better water quality and a wider variety of insects. Image by Aminetth Sánchez.

Chinampas: The center of the action

The chinampa refuges are the protagonists of this story. In 2008, the UNAM laboratory began to foster the transformation of these floating pieces of land with rehabilitated canals to improve the lives of axolotls and other native species. These are special sites to promote the restoration of axolotl habitat and allow the amphibians to complete the three stages of their life cycle: embryonic, larval and adult (when the process of reproduction usually occurs). These sites are far from the threat of their predators and far from poor-quality water.

“The approach consisted of considering the chinampa and the secondary canals, or trenches, as environmental units whose interaction is very dependent on each other,” according to the master plan for the project. “In other words, the activities that are developed on a chinampa directly influence the quality of the secondary canals, and this, in turn, influences the conservation of the agricultural capacity of the chinampas.”

These types of chinampa refuges have two main characteristics. The first is that the secondary canals that surround the pieces of land have a gate at the front to prevent carp and tilapia from entering. This structure, made from a wooden frame and a plastic net, guarantees that the water from the main canal, or acalote, mixes with the water from the secondary canal, but without providing access to invasive species. The second characteristic is that, on the shores of the land, Bonpland willow trees (Salix bonplandiana) are planted and stakes are installed to stabilize the land and prevent it from breaking into fragments. Technical protocols are the basis for these actions.

Once the land is in place and the canals are rehabilitated, plants are brought in to act as biofilters. This technique involves using aquatic plants like bulrush (Schoenoplectus americanus) and broadleaf cattail (Typha latifolia) to clean the water. As the plants’ roots grow, they serve as natural barriers, in addition to the gates, to help keep out invasive species.

“The result is clean water, of very high quality, where axolotls, frogs and other very small animals — very sensitive to pollutants — live,” says Felipe Barrera, a chinampero. “This is our indicator that we are doing things well.”

Felipe Barrera’s chinampa measures about a tenth of a hectare, or a quarter acre. In the middle and along its edges, it contains restored spaces that function as refuges. Image by Aminetth Sánchez.

Not just any chinampa can function as a refuge. The minimum requirements to achieve this status are sufficient water quality and level, agrochemical-free farming, agriculture-based land use, and a committed chinampero. “Here, planting is an art,” says Basilio Rodríguez.

During the first stage of the project, from January to May 2012, a quarter hectare of chinampas was rehabilitated. The impact? Parts of the area around the lake at Xochimilco improved, food production increased, certain canals and trenches recovered, habitats were rehabilitated, and the water condition in some areas improved.

In 2014, the lab conducted a workshop with farmers to teach them the chinampa refuge model and the production of organic fertilizers, biofertilizers and pest control substances. As a result, many of the farmers went on to dig trenches that ended up serving as refuges for axolotls.

The goal: To transform 400 chinampas

Fifteen years since the launch of this project, the results have been encouraging: 40 rehabilitated chinampas, 36 refuges, 71 biofilters built, 12 hectares (30 acres) of land planted, 228 direct beneficiaries (chinamperos and their families), and 912 indirect beneficiaries (day laborers who work on chinampas). The researchers say they’re determined to improve even more.

“What we would like is to have about 400 chinampas in the next 15 years,” Zambrano says. “There is space for this, [and there are] also possibilities and economic abilities to do this. The only things left are a little [bit of] political will and some work with the government.”

Each refuge is in a different stage, according to Sumano. Some are in the chinampa rehabilitation phase, and others already have some axolotl populations. The time it takes to transform the spaces varies, since each chinampero has different economic resources and available time.

A model of the structure of a chinampa refuge, top, and an example of a gate at the entry to the secondary canals. Images courtesy of UNAM Ecological Restoration Laboratory.

Basilio Rodríguez harks back to four years ago, when his chinampa was level with the water and looked like a pond. Together with the researchers, he reconstructed the patch of land, removed the sediment, aligned some stakes and filled in the holes. “Now the land looks beautiful,” he says.

There’s no uniform design for the refuges. Since the sizes of each plot of land and their distributions vary, some people focus only on the canals that surround the land, while others put small refuges above the chinampas as if they were small ponds.

Sumano, who manages the initiative in the field, knows by heart the status of each chinampa refuge, its location, and even its owners’ lunch schedules.

“We are working with Basilio; his refuge is in an intermediate stage. He is working a lot on the agricultural part, but the refuge is still lacking. We are hoping to finish consolidating it this year,” he says, dressed in a white shirt and denim jeans as he zips through the canals of Xochimilco on his canoe.

“This is Mr. Felipe’s refuge; it was one of the first ones. How old is it? About seven years. He wanted to make his refuge above the chinampa,” Sumano says as he tethers his canoe to a tree.

Recovering chinampas; recovering the ecosystem

Older locals say the chinampas in Xochimilco used to measure 10 by 100 meters (33 by 330 feet). This was the most common configuration, about one-seventh the size of a professional soccer field. Felipe Barrera’s chinampa refuge is exactly this size. Here, he grows corn, Aztec marigolds, mint and much more. There’s diversity among the plants, insects and even the water quality. For a chinampero, it’s paradise. “When we talk about a healthy ecosystem, it is this way, just like this: diverse,” Sumano says.

The plan to restore his chinampa began seven years ago, after Barrera returned to Xochimilco to restart his family’s tradition of working with chinampas. The first step was to find a way to gather clean water. “I began to collect rainwater in tanks that, [although] they are not exactly a secondary canal, they can serve as storage,” the 47-year-old says in a vibrant voice.

He later joined forces with the team from the UNAM laboratory and Pedro Méndez, another chinampero, to work on the restoration of the secondary canals, known as apantles, which provide water for the crops. The premise of this scientific project is that nothing can be achieved without the participation of local farmers and residents. It’s a project by everyone, for everyone.

The impact of the chinampa refuges on the area directly translates into better water quality, superior crops, a more bountiful harvest, wider economic benefits, and, as a result, a greater appreciation for the land, according to Rivas from UNAM. Having better water quality also fosters greater diversity and a healthier ecosystem, which can act as a buffer zone against climate change.

Sumano dips his hand into one of the secondary canals at Barrera’s chinampa refuge, in which he estimates that about 500,000 pesos ($30,000) has been invested. The water looks different: crystalline, clear and see-through. There’s a smell of vegetation, and the plants’ roots are white. There’s a variety of aquatic fauna, such as water bugs and small crustaceans. This image is very different from the green-blue water in the main canal of Xochimilco, where the roots are dark from the dissolved solids and pollutants contaminating the water.

Carlos Sumano, who manages the ecological restoration project in the field, knows by heart the status of each chinampa refuge, its location and even its owners’ lunch schedules. Image by Aminetth Sánchez.

“Once we see insects present on the plants, especially on the root area, we can begin to have small fish, acociles [and] larger fauna. And in the end, if everything is restored, we can have axolotls, because the ecosystem is working,” Sumano says.

This is what many of the farmers also want. They share the dream that their ecosystems will succeed. However, their work isn’t over with the launch of a refuge. Monitoring, evaluation, maintenance, the use of biofertilizers and organic fertilizers, and the use of mud to germinate seeds are some of the tasks that they must continue to carry out to be part of this network. These tasks can also result in the produce harvested from their chinampas being granted an ecological distinction called a “Chinampera Label.” It’s not a formal certification, but it recognizes their agroecological quality.

This distinction can only be obtained by chinamperos whose harvests have earned a total score of 53 points in terms of the quality of their water, their chinampas’ production and their refuges. There are three levels that define the progress of their refuges. Claudia Medina, Cassandra Garduño, Basilio Rodríguez and Felipe Barrera are some of the 18 farmers who now hold this title and can sell their produce at Tienda UNAM, the supermarket at the National Autonomous University of Mexico.

“More marketing spaces are opening for consumers who want these types of products. And the chinamperos themselves have marketing strategies [and] their own clients, and this distinction allows them to have security,” Sumano says. In addition, this distinction is a source of economic strength for a project that, year after year, has sought funding from governments, companies, organizations and initiatives to continue.

After 15 years of this work, the laboratory is clear that the most significant achievement is that there’s now a model for restoration with evident benefits in bodies of water.

“It is a living example of how humanity can coexist in an ecosystem, producing food, meeting its needs, and, at the same time, conserving and respecting the environment,” Sumano says with excitement. “It is possible to do so; the chinampa is an example of [the idea] that this is real, that it is possible, that it can be done, that it works.”

Banner image: Basilio Rodríguez has been a chinampero since childhood. His current work is the building of a refuge to help conserve the axolotl. Image by Aminetth Sánchez.

This story was reported by Mongabay’s Latam team and first published here on our Latam site on Feb. 13, 2024.

Citation:

Voss, S. R., Woodcock, M. R., & Zambrano, L. (2015). A tale of two axolotls. BioScience65(12), 1134-1140. doi:10.1093/biosci/biv153

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