- A group of researchers studied that the rise in sea level and the change in aquifer recharge in Yucatán will increase the salinity of groundwater, the only source of supply in the peninsula.
- According to their calculations, in 2100, people on the coast will not find fresh water until they are about 18 kilometers away from the point where the waves break.
- In an extreme scenario, salt intrusion into the aquifer will prevent the reproduction of species such as flamingos.
- This problem is developing in the midst of a social crisis generated by the increase in tourism and real estate developments that have displaced local populations farther and farther from the coast.
Irineo Novelo, district commissioner of Sisal, remembers that it was easy to find fresh water as a child: it was enough for his dad to dig a hole in the sand or his grandfather dig a well a meter and a half out of the sea to observe the clear water, take it with his hands and satisfy his thirst.
He doesn't remember exactly the moment when that became exceptional, he only knows from a mental calculation that 58 years had passed. Several of the wells that exist in Sisal - a coastal town in the state of Yucatán, in the Gulf of Mexico - have been converted into latrines since the water that comes out of them began to smell and taste like salt, a phenomenon known as “salinization”.
Irineo Novelo. Photo: Miguel Guillermo.
Although this is already a reality in several areas of the Yucatan coast, the problem will worsen, experts say. In October 2024, a group of researchers concluded in an article that rising sea levels and changes in the recharge of the freshwater aquifer in Yucatán (the process of storing water in the subsoil) will increase groundwater salinity causing “complex socio-economic and environmental consequences” on the northwestern coast, where Sisal is located. This is especially important considering that groundwater is the most important and practically the only source of supply in the Yucatan Peninsula.
For now, the town of Sisal continues to supply itself with fresh water that comes out of a well located six kilometers inland from the beach line. However, that supply is not guaranteed in the long term. Everything indicates that over time he will also be compromised.
The situation takes on special relevance at a time when the town is at the center of social tensions, because its inhabitants claim coastal land as their own to prevent them from ending up in possession of real estate. In this process, federal authorities accuse them of felling two hectares of mangroves, something that the villagers deny. For these facts, the Attorney General's Office (FGR) opened an investigation. These ecosystems act as a natural barrier that is key to regulating coastal salinity.
When the aquifer becomes salty
In every coastal aquifer, there is a natural movement of fresh water to the sea. This is how fresh water mixes progressively with salt water. In aquifers such as the one in the Yucatan Peninsula, the thickness of this mixture, called the salt interface, is thin and ranges from 1 to 1.5 meters deep, explains the researcher at the National Autonomous University of Mexico, César Canul-Macario.
When it happens that, due to some natural phenomenon or human action, the sea begins to gain space, that salt interface changes. “In this case, the salt intrusion implies that the sea is gaining space for the freshwater aquifer,” says Canul-Macario, “and waters that were not salty before are beginning to present salinities that may not be suitable for human consumption,” he explains.
In 2020, César Canul-Macario observed saltwater entering the first kilometers of the aquifer near the northwestern coast of Yucatán, where Sisal is located, and predicted how salt intrusion will progress in the years 2040, 2060 and 2100. According to their calculations, in 2100, people on the coast will not find fresh water until they are 18 kilometers away from the point where the waves break.
Photo: Miguel Guillermo.
The rise in sea level and changes in rainfall, two scenarios caused by the climate crisis, are the origin of this problem and will continue to affect the distribution of salinity in the coastal aquifer and the quality of the water, supposes the Canul-Macario study. In fact, by 2040, the researcher assures, vital areas of the aquifer will be compromised, such as the primary source of public water supply in Sisal. This year, he indicates, the water that supplies the population will exceed the permitted global and local concentrations of minerals, salts and dissolved metals.
Canul-Macario's research was based on data from the International Panel on Climate Change (IPCC), the main scientific body that provides the necessary information to the decision makers that make up the United Nations Framework Convention on Climate Change.
The IPCC has projected a sea level rise of between 40 and 80 centimeters by the year 2100 on the coast of the Yucatan Peninsula. In addition, it foresees changes in the hydrological regime, that is, in the rains, which could affect the supply of the aquifer. According to Canul-Macario, in an aquifer such as that of Yucatán, where the hydraulic gradients (that is, the inclination between the water of the continent and the water of the sea) are very flat, an increase of up to 80 centimeters has great implications, since even a small increase in the average sea level generates important changes in the aquifer.
Long-term monitoring
The biologist Erick Soto, a technician at the UNAM, is responsible for monitoring salinity in nine wells in the Yucatan Peninsula. When you reach one of the Sisal wells, take out a reel and place an oceanographic instrument at its tip that allows you to measure the conductivity, temperature and depth of the water. He drops the reel into the well and the instrument drops rapidly until it touches the water, 17 meters deep.
Biologist Erick Soto monitors nine wells. Photo: Miguel Guillermo.
After taking a water sample, connect the device to a computer that calculates the data. While presenting the findings, the scientist explains that in the aquifer, fresh water is kept at the top because it has a low density. Saltwater, on the other hand, stays below because of the higher density that salt gives it. If the oceanographic instrument used by Soto shows an increase in salinity levels compared to previous records, it means that salt intrusion has increased, that is, that salt water is gaining space.
The work that Soto does obtains a profile of water pressure, conductivity and temperature, variables necessary to study characteristics of the ocean such as its salinity, density and chemical composition.
One of the wells monitored by Soto. Photo: Miguel Guillermo.
During the monitoring, Soto recorded seawater 16 meters deep in two wells. The first one is located 291 meters from the sea; while the second one is 4.73 kilometers away.
Graphic credit: Dr. Roger Pacheco
“For me it's critical,” he says, referring to the well that is more than four kilometers from the beach. “At less than five meters (depth), salinity changes up to 22 grams per liter. Seawater has 36 grams of salinity. I have higher brackish water than the mangrove forest,” he says.
“In the well located at 291 meters, it varies much more and that is also serious,” he says.” It is not the same thing that the salinity starts at 10 meters as at 12 meters. Here they can run out of water sooner.”
The well that feeds fresh water to Sisal is six kilometers inland on the Sisal-Hunucmán highway. “This area that supplies the coastal population shows significant reductions in the thickness of fresh water, so that by 2100 the extraction of fresh water in this area would not be feasible,” explains the latest study by Canul-Macario.
Until a few days ago, Irineo Novelo was unaware of the projections of the Canul-Macario studio. “It would be nice to be informed. We should know what is being done and what information we have about Sisal,” he says. He is clear that because they are located close to the ocean, coastal populations are more vulnerable and completely dependent on aquifers for drinking water.
In August 2024, the population of Sisal, of almost 2100 people, was left without a pipe to provide water to their homes for a month because of a fire. That experience, Irineo says, “confirmed how vulnerable we are.” “I had to see where to get to in order to have access to water. I had to keep an eye on the pipes and sometimes give for refreshments so that the water reaches your tank. Since you don't have the famous wells in the patios, you have to search and fix yourself so that you have the water here in the house and bathe, cook, wash. Water is needed even for the most basic things, such as processing corn for tortillas,” he adds.
Biologist Erick Soto agrees with Novelo regarding the lack of dissemination of the topic and recognizes the importance of people monitoring their wells in the future. That, he explains, would allow them to obtain evidence to ensure better water quality and the survival of vital species on the coast.
“There are people who ask me: 'How is my well? ' , and for me that participation is what gives importance to the study. A man told me that the water at the height of a well 64 meters inland in Sisal was fresh and now it is no longer. These are issues that they themselves have noticed over the years, but there is a lack of data to corroborate and make requests,” he explains.
In addition, salinization also impacts ecosystems. From the smallest organisms such as crustaceans, mollusks or some bacteria to larger ones such as flamingos. Recently, flamingos were distributed in other areas when they normally arrive in Celestún. The increase in salinity to the north in the different ecosystems meant that there was food before and they were left behind in several locations, Soto says.
Phytoplankton, one of flamingos' favorite foods, dehydrates with increasing salinity. “It's like when you bathe and your fingers wrinkle, we can handle it, but there are organisms that don't,” says the biologist.
“Mangroves or swamps are the most affected,” Soto says. The Chelemeras - a group of Mayan women who restore mangroves in Chelem, Yucatán - told Soto that there were mangroves that did not exist even if they set the correct salinity due to the intrusion generated by rising sea levels.
Soto believes that in the future it should be the citizens who monitor the wells. Photo: Miguel Guillermo.
In the end, the entire cycle is affected: “Let's remember that sperm and eggs are cells. There are many organisms that go and introduce their eggs or reproduce in mangroves towards the aquifer. The increase in salinity affects the perfect composition to absorb and they die or their organisms simply cannot develop because there is never fertilization. That's a little more extreme. If salinity progresses, they won't be able to reproduce,” he explains.
We can't take long
In Tulum, located in the state of Quintana Roo, also on the Yucatan Peninsula, it is common for tourists to brush their teeth with bottled water from hotels. In untouristic neighborhoods such as Mayapax, Los Huracanes and Villas Tulum, on the other hand, residents can spend up to eight days with salty and yellowish water coming out of the faucet.
To solve the problem, in 2023, the installation of two desalination plants was announced in Quintana Roo: one in Tulum and the other in Cozumel, with the capacity to desalinate 50 liters of brackish water per second.
This strategy is one of the options proposed by César Canul-Macario for the northwestern coast of Yucatán in the future, when increased salinity reduces the thickness of the fresh water that is still available to the population.
The costs depend on the quality of the salt in the water. “Right now they still have fresh water, but in a very adverse scenario they would have completely salty water, which is where painting is starting to be much more expensive. On average worldwide, one cubic meter of desalinated water is around two or three dollars. Plus the cost of taking it home,” says the researcher.
In his studies, Canul-Macario also proposes other options such as waterproof walls along the coast to control saltwater intrusion, the collection of rain or the artificial recharge of fresh water. However, it has reached similar conclusions: the increase in salinity translates into an increase in the prices of drinking water given the costs of operation and maintenance.
Although the scenarios that Canul-Macario projected in his study are not immediate, he insists on the need to act quickly considering that there are other variables that also contribute to the salinization of the aquifer. For example, the increase in demand for fresh water due to the accelerated growth of the population, tourism and the real estate sector in the region.
For this note, Cristina Pérez Bojórquez, mayor of Hunucmán, the municipality to which Sisal belongs, was personally requested to interview Cristina Pérez Bojórquez. However, his assistant evaded setting a date. The only thing he argued on the subject, during a tour of environmental authorities in Sisal, was: “It's something that cooperatives have expressed because the places where they lead to tourism (are affected)”.
Irineo Novelo fears that the reality of his community will become like that of Ciudad del Carmen or Tulum, where they depend on desalination plants. “I hope that science will have more advanced ways to make seawater suitable for human consumption,” he says concerned.
* This text was made possible thanks to the financial support and editorial support of Mongabay and Causa Natura.
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