This fragile wetland is dying. Tour boats could be its unlikely saviour.

Piloted by gondoliers, colorful tour boats called trajineras, runs along a sun-spotted canal. They drift past serenaded mariachi musicians in their own boats and vendors selling snacks from wooden canoes.

This carnival scene takes place most weekends from Xochimilco (pronounced “zo-chee-MILK-oh”) – a Unesco World Heritage and a popular destination for tourists in southern Mexico City. eleven percent of the country’s biodiversity is found in this 6,400-acre wetland threaded by 105 miles of pre-Hispanic canals. It is a fact that some of the approximately two million tourists and chilangos (slang for Mexico City residents) who visit in a normal year know this before boarding the trajineras for an afternoon cruise.

But this fragile ecosystem faces an uncertain future, as pollution built over decades extracts life from these waterways, threatening a living heritage.

In a surprising twist, Xochimilco’s trajinera tourists could be the wetland’s unlikely saviors, if a local plan to use these wooden vessels to purify the murkiest depths of the canals takes off.

An ecosystem in danger

The Xochimilco wetland is considered one of the last living links with the Aztecsthanks to the reserve remarkable floating farms known as chinampas. Humans built these islands – 5,475 acres – from the nutrient-rich soil in the channel beds, making the chinampas one of the most productive types of agriculture in the world. In Mexico, they have fed the capital for a millennium.

Today, about 55 tons of chinampa-grown vegetables – from beets to native crops such as talamayota squash – fill the trestle tables daily at Mexico City’s neighborhood markets and sprawling wholesale supplier Central de Abastos de la Ciudad.

“Xochimilco has it all. It gives food and water, regulates the capital’s climate and mitigates flooding, provides work and is rooted in tradition,” explains Claudia Alejandra Ponce de León, professor of environmental sciences at the National Autonomous University of Mexico.

Yet the water used to grow these fruits and vegetables has been full of pathogens for years, says Refugio Rodriguez Vázquez, a clean water activist and professor of biotechnology at Mexico University. National Polytechnic Institutewho started studying the wetland in 2016.

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Vázquez says a toxic cocktail of agrochemicals from runoff and wastewater from land and floating farms is to blame. Sewage is dumped from El Cerro de la Estrella and three smaller treatment plants within a 12-mile radius into the canals at an alarming rate of 2,000 liters per second, she said. That’s enough to fill an 8 foot deep pool measuring 2.5 feet by 2 feet every second.

Compounding the problem, nitrogen and phosphorus from these sources proliferate algal blooms consisting of slow water (duckweed) and lirio acuático (water lily) — the latter, introduced in the 1980s by the then Mexican president “for decoration,” proved to be a problematic invasive species.

These flowers carpet the surface of the water, blocking out the sun and oxygen. “When [the algae] dies, it settles at the bottom of the channel in the form of sediment. This breeding ground of methane-producing bacteria then releases greenhouse gas in the atmosphere,” explains Vázquez.

“According to the Canadian government, our polluted canals make migratory birds like the mexican duck and the really sick great blue heron,” adds Armando Tovar Garza, biologist at Humedalia, a local conservation organization. Ecological degradation has already driven endemic species like the axolotl salamander to the brink of extinction in Xochimilco. “Wetlands are important for maintaining the quality of life in Mexico City as we know it,” says Garza.

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Xochimilco’s problems began 40 years ago, when the authorities bled its natural springs dry to supply Mexico City’s burgeoning population, then filled the canals with treated water. The toxic mix is ​​aggravated by illicit wastewater discharges from informal neighborhoods in the borough.

“This land has sunk six meters in the last two decades due to the extraction of water from aquifers towards Mexico City,” said Luis Martínez, a third generation chinampero, who grows 15 varieties of vegetables on her 2.5-acre plot in San Gregorio. “We desperately need to improve water quality.”

A modern solution for an old waterway

If all goes well, an ambitious plan to harness the power of tiny bubbles – delivered by tourist boats – could restore the wetland’s channels and have implications beyond Xochimilco.

“The nanobubbles can penetrate this muddy sediment,” says Vázquez. About 2,500 times smaller than a grain of table salt, these microscopic air pockets literally breathe life into oxygen-starved waters, “staying for up to six months…in the right conditions,” says Vazquez.

Since their discovery in the 1990s, nanobubbles have been used to remove pollutants in many industries including biopharmaceuticals and food processing. Because nanobubbles have no natural buoyancy, they stay underwater, where each tiny negatively charged bubble is attracted to positively charged pollutants and harmful toxins. This union causes the nanobubbles to release hydroxyl radicals, which can quench pathogens and slowly break down algae cell walls.

To deliver the bubbles, Vázquez designed a guerrilla-style installation of pipes and solar panels that harnesses the wetland’s existing tourist infrastructure – the trajineras, all of which number 1,103.

These motorless boats (seating up to 20 people) provide an essential stream of income for an entire community of musicians, floating chefs and remeros like Jose Gabriel Gonzales Franco. The fifth generation gondolier is a descendant of the Xochimilcas who lived here long before the arrival of the Aztecs. The Remero people still make godwit poles as their ancestors did, using wood from the endemic oyamel tree. “We own this land,” Franco says. “We [remeros] keep the tradition here.

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So far, Vázquez has only tested the prototypes in his canalside workshop and floating lab (a recycled trajinera baptized “little bird”). However, extensive computer models using a controlled study in a swimming pool, along with tons of supporting research, show that the app was successful in cleaning up polluted water.

A sweltering Saturday in October 2021 marked the first time the installation was installed on a trajinera with tourists on board. Two 50-watt solar panels have been fixed to the curved roof of the boat owned by Carlos Díaz, whose family has been ferrying visitors along the Cuemanco and La Cruz canals from the Flores Nativitas pier since 1960.

A tangle of wires connects the panels to a small control box, which creates photovoltaic energy. This powers a pump in the submerged tubes, which in turn is designed to pull water out of the channel, redistributing it as thousands of COVID-19 particle-sized bubbles. Vázquez says one aspect of his long-term plan is to communicate the project’s message in a series of infographics attached under the roof of each boat.

The following week, Vázquez and his team of PhD students took the setup out into the field to make sure all the moving parts worked together. This time they outfitted a fleet of tour boats carrying a group of scholars curious to see his invention in action. The flotilla set off from the Puenta de Urrutia pier, gateway to some of Xochimilco’s famous floating farms.

Beyond Xochimilco

Fortunately, the setup worked – a small but mighty victory in what promises to be a tough road for Vázquez, who must patent his homemade technology and get the local government on board.

It has not yet been possible to draw definitive data from the trial, mainly due to its very small scale. Additionally, it will likely take several months for the benefits of oxygenated waters to be tangible, due to the sheer volume of algal blooms. Still, hopes are high that the pump will succeed in achieving Vázquez’s goal of cleaning up a third of Xochimilco’s canal system.

Although there is still a long way to go, the academic community in Mexico and beyond is already considering other possible applications for Vázquez’s invention. Jordi Morató Farreras, coordinator of the UNESCO Chair in Sustainability at Polytechnic University of Cataloniasays he can imagine leveraging the technology in other protected destinations.

Oxygenating a lake in Colombia and decontaminating agricultural soils closer to home in the state of Puebla are just some of the ideas that many are floating around.

It would be a pride for the inhabitants. “I first went to Xochimilco eight years ago and was amazed by the amount of trajineras, the color of the water and the pollution of the water,” says Gabriela Vianey, a teacher at the local primary school, aboard the trajinera trial course. “I had no knowledge [Vázquez’s] project to date. I hope so [Xochimilco] will be there for my children’s children to see.

Sarah Freeman is a UK-based journalist focusing on conservation travel. Follow her on instagram.

Earnest A. Martinez