Groundwater is water systems that took millions of years to form and gave rise to large reservoirs, such as the Guarani Aquifer .
Considered the second largest source of freshwater in the world, it covers international lands in the territories of Argentina, Uruguay and Paraguay and Brazilian lands in the states of Goiás, Minas Gerais, Mato Grosso, Mato Grosso do Sul, São Paulo, Paraná, Santa Catarina and Rio Grande do Sul.
Qualified at times as a gigantic Mercosur “underground lake”, as it extends under the subsoil of the four countries forming this economic block, the Guarani aquifer has an area of 1.2 million km 2 and consists of spills of basalts, sandy sediments and sandstones.
Its average thickness is 250 m, reaching more than 800 m in some points; it is estimated that the water reserve is 45 thousand km 3 , that is, 45 quadrillion liters, more than all the rivers on the planet transport over a year. For all these reasons, it constitutes an invaluable reserve for South America, for the supply of the population and for the economic growth of the countries involved.
The water stored in the Guarani Aquifer comes from rain that falls on the surface and seeps underground. In this process, the liquid passes through porous rocks forming this important water table, which can be found thousands of meters deep.
The geological formation of the terrain favored the formation of the Guarani Aquifer, since, in the area, there is a porous sedimentary rock – the sandstone – that allows water to infiltrate.
At the same time, below the surface, there is basalt – magmatic rock – which is impermeable, preventing the water that passes through the sandstone to disperse in deeper regions, functioning as a “wall”, which keeps the water between the sandstone and it .
Other Brazilian aquifers
According to Prozipcodes, in Brazil, due to the ancient relief, there are many porous rocks, such as sandstones, siltstones and clays, which facilitate the formation of aquifers in the territory.
In addition to Guarani, aquifers are found in almost all regions of Brazil, including in semiarid regions, such as the interior of the Northeast. Q lmost 50% of the territory corresponds to sedimentary areas with permeable rocks, where the water underground are relatively abundant. Such rocks contain about 4 trillion m 3 of fresh groundwater, protected from periodic droughts that plague the semiarid region.
States such as Maranhão and Piauí, for example, are based on the large sedimentary basin Parnaíba-Maranhão, with an estimated volume of available water of 17,500 km 3 . Other large freshwater reserves in the subsoil are the Tucano-Jatobá basin, on the border between Bahia and Pernambuco; the Chapada do Araripe, between Ceará, Pernambuco and Piauí; the Chapada do Urucuia, on the border of Bahia with Mato Grosso do Sul, and the Chapada do Irecê, in Bahia. And even in the crystalline terrain there are sedimentary stretches, in which the probability of having access to aquifers is high.
Another gigantic underground reservoir, which is considered the largest in the world, was called the Alter do Chão aquifer , located in the states of Pará, Amapá and Amazonas and has almost twice the amount stored in the Guarani aquifer, 86 thousand km 3 or 86 quadrillion liters.
Threat to aquifers
Since the beginning of civilization, humanity has used and explored groundwater for its own consumption and to irrigate its crops. However, with the increase in the world population, especially after the industrial revolution that started in the 18th century, consumption has grown so intensely that the water potential of the globe may become insufficient to meet the most basic needs.
The great economic growth, especially in the southeast of Brazil, as in the Ribeirão Preto region where Guarani flourishes, increased the demand for water. The result is that the aquifer has been decreasing, since demand exceeds supply.
The technicians also warn of the risks of contamination of the aquifers by pesticides or fuels, especially through abandoned or poorly constructed wells.