When we talk about water reserves, we're not just referring to the water available in rivers, lakes, or reservoirs, but also to groundwater reserves found in aquifers. However, many people don't know exactly what an aquifer is , nor the enormous importance they have for the sustainability of freshwater on the planet.
In this detailed article, we will explain what an aquifer is, how they are formed, the different types that exist, their ecological relevance and their crucial role in water supply. We will also look at the threats that aquifers face and how it is possible to manage them sustainably.
What is an aquifer
An aquifer is a geological formation that has the capacity to store and transmit groundwater. It is composed of permeable materials, such as sand and gravel, which allow water to flow through their pores. Aquifers play a fundamental role in the hydrological cycle , as they help feed surface water sources such as springs, rivers, and lakes.
Aquifers are located in the zone known as the saturated zone , which is the area where the pores or fissures in the rock are completely filled with water. The amount of water an aquifer can store depends on its porosity, and its capacity to transmit water is determined by the permeability of the materials that compose it.
The importance of aquifers lies not only in their storage capacity but also in the quality of the water they contain. Because they are underground, aquifer water is usually free of contaminants and suspended solids, making it one of the purest sources of drinking water.
Formation of aquifers
Aquifers form through the process of water infiltration, typically from precipitation (rain or snow). When rainwater falls to the ground, some of it flows into surface water bodies, while some infiltrates the soil and descends until it reaches a layer of permeable rock. This process is part of the water cycle and is driven by two important factors: gravity and lithology (the nature of the rocks).
Water typically continues to flow downwards until it reaches a layer of impermeable rock, such as clay or granite, which blocks its passage to deeper layers. In areas where water accumulates, an aquifer forms . Depending on the porosity of the rock layers, water can circulate through them, creating a water reserve that in many cases can be used for human consumption, irrigation, or even industry.
Types of aquifers
Aquifers can be classified according to several criteria. The most common is the type of hydrostatic pressure they contain, which divides aquifers into unconfined, confined, and semi-confined.
- Free aquifers: Also known as unconfined aquifers, these aquifers are in direct contact with the atmosphere, and the water they contain is at atmospheric pressure. The permeability of the covering material allows water to easily circulate to the surface.
- Confined aquifers: They are bounded by impermeable layers that enclose them both above and below, which generates a pressure greater than atmospheric pressure on the water. When a well is drilled into a confined aquifer, the water can naturally rise due to internal pressure.
- Semi-confined aquifersThey have a semipermeable upper layer, which allows water recharge, but less easily than in free aquifers.
Importance of aquifers
Aquifers are vital for water supply in different parts of the world. It is estimated that more than 2.500 billion people depend exclusively on groundwater to meet their drinking water needs. Furthermore, they are a crucial source for irrigated agriculture , which accounts for more than 67% of the water used in food production.
Another important point is the role of aquifers in regulating the water cycle . During periods of drought, aquifers can release water to maintain the levels of rivers, wetlands, and lakes, which in turn helps sustain biodiversity in these ecosystems. Therefore, their preservation is vital not only for human water supply but also for environmental sustainability.
Flora and fauna in aquifers
Aquifers are not only important for the water they provide, but also because they are home to unique biodiversity. Although they are dark and light-deprived environments, many species of microorganisms and small animals have developed adaptations to survive underground.
Among the most common species are invertebrates such as rotifers and oligochaetes . However, mammals and reptiles also visit these ecosystems in search of water. Furthermore, plants with deep roots, known as stratophytes , are able to access groundwater.
Threats to aquifers
Unfortunately, aquifers are being threatened by various human activities, including:
- Overexploitation: Water extraction from aquifers is often greater than the natural rate of recharge, which depletes these reserves and causes land subsidence.
- Contamination: Fertilizers and pesticides used in agriculture, as well as industrial and urban waste, are filtering into groundwater, contaminating these sources with toxic substances.
- Salt intrusion in coastal areasIn regions close to the sea, uncontrolled extraction of groundwater has allowed salt water to invade aquifers, making the water unusable for human consumption.
Differences between aquifers and springs
It's important to distinguish between aquifers and springs . While springs are points where groundwater naturally emerges to the surface, aquifers are underground formations that store water. A spring may depend on the flow from an aquifer, but not all aquifers form springs.
Springs are usually more accessible and visible, while aquifers, being underground, require hydrogeological studies to be located and managed appropriately.
The water that flows from a spring varies according to the season of the year and the amount of rainfall, since it is fed by the same aquifers that capture rainwater.
Hydrogeological investigations allow us to determine an aquifer's capacity and its health. That is, whether it is overexploited, whether the water quality is good, or whether its use needs to be regulated.
The study of these systems is crucial to implement policies that prevent the decline of these essential resources for life on Earth.
Aquifers represent one of the most resilient, but also vulnerable, key sources of water. Sustainable management is essential to ensure that future generations can access clean water.