Although they are global, the effects of climate change caused by human activity are increasingly felt at a local scale, as happens at the Potosí basin, a dry region in Nuevo León where there has been a perennial fire for 30 years.
According to Priyadarsi Debajyoti Roy, a researcher at the Geology Institute of the National Autonomous University of Mexico (UNAM), the Potosí basin was not always a dry area.
Over 16,000 years ago, it used to be a wetland that contained a vast amount of biomass. Nevertheless, with the change of vegetation from trees to bushes, 11,000 years ago, and from bushes to grasses, 4,000 years ago, it became a semi-arid region.
“In less than 40 years, that ecosystem, that used to have runoffs that fed the aquifers, was devastated by diverse human activities,” he added.
Land-use changes (traditional agriculture was abandoned) in that region surrounded by the Sierra Madre Oriental has led to the constant extraction of underground water to irrigate the industrial agricultural fields with plants that require a lot of vital liquid, such as tomato, onion, potato, chili pepper, and alfalfa.
The over-extraction of water made the phreatic level to go down, at least, from 5 to 80 meters in a part of the Potosí basin, where there was still superficial water in the 1980s.
“Aquifer overexploitation also caused more desertification; from 1980 to date, it increased in several areas from two to three times and cultivation areas became six times smaller. Moreover, coverage from native bushes was reduced by four times,” as asserted Roy.
Peat
Another anthropic factor that worsens the ecosystem of the Potosí basin is the burning of peat, a sedimentary layer rich in organic matter that was formed thousands of years ago.
“Yes, 30 years ago, a spark that jumped out of the traditional burning of excess agriculture biomass lit the peat that was on the surface. Since then, the relentless combustion has been emitting carbon dioxide and other greenhouse gases that are harmful to the health of nearby communities,” as explained by the researcher.
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On top of that, by making the subsoil hollow, the underground burning of peat caused the collapse of the ground and, later, the generation of subsidence or vertical sinking with diameters from 10 to 20 meters. There are so many subsidences that, from 1980 to 2020, the land without use grew from 2 square km to 340. And the cultivation area, which used to measure 90 square km in 1980, is not currently only 16 square km.
“The area has become a desert due to the change in land use,” warned Roy.
Water pollution
Part of the fertilizers used for industrial agriculture to make crops more productive permeates into the aquifers and pollutes underground water. According to the World Health Organization (WHO), in order to water to be drinkable, it must contain specific concentrations of certain elements.
If nitrate surpasses 50 milligrams per liter (mg/l), it affects the health (in newborns, oxygen is reduced in the blood and produces the blue baby syndrome). If fluoride, which concentration should be of 0.9 mg/l, surpasses 1.5 mg/l, it causes fluorosis, calcification of ligaments, and bone deformation. If sulfate surpasses 600 mg/l, it can cause diarrhea and dehydration.
Water studies performed by the researcher and his colleagues at the Potosí basin show that fluoride surpasses the desired measure.
In several Wells, nitrate has reached 10 mg/l due to the fertilizers used in agriculture. That concentration does not directly affect health but it could increase with time.
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The Potosí basin does not have so much nitrate but nearby, at the Aramberri municipality, also in Nuevo León, there is another basin where this salt’s concentration is of 180 mg/l, that is thrice as what the WHO recommends to avoid blue baby syndrome.
“As of ammonium, which affects the water’s flavor and smell, the desired concentration is 0.2 mg/l. It is five times bigger there; which proves fertilizers, livestock, and septic tanks are also contaminating underground water,” said Roy.
Mist capture
During the ice age with cold environments, 20,000 to 30,000 years ago, water recharge at the Potosí basin took place through the underwater flow. In the last 11,000 years, natural climate change modified that hydrological dynamic.
Nowadays, water recharge in that basin is through surface runoff. However, due to its terrain, located at the skirts of the Sierra Madre Oriental, and due to global warming, the amount of water is less; likewise, due to the increase of temperature, the few runoffs evaporate before arriving at the basin.
“In order for that ecosystem to be sustainable once again, we should let it recover with as few human disturbances as possible. And for that, we would have to avoid extracting underground water and not using the basin for industrial agriculture activities, which would certainly affect the region’s economy. Regarding the people who live there, it would be best for them to migrate to other places in the country for they have been breathing the fire’s toxic gases for 30 years,” said Roy.
That said, eliminating industrial agriculture and moving people are two processes that should take place gradually and with the consensus of the inhabitants and the farmers as well as with the participation of the three government levels and NGOs. Meanwhile, since it is a dry area, it needs an alternative source of drinking water for the communities that are established there.
“There could be net to capture mist up high the Sierra Madre Oriental to obtain water for domestic use and traditional agriculture, as has successfully happened in arid regions in Israel, Chile, and Peru,” said the UNAM researcher.
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