Tomás Aquino wins an ERC to understand the flow of water and contaminants in the soil

The IDAEA researcher Tomás Aquino has just obtained a prestigious ERC Starting Grant from the European Research Council to understand the transport of water, pollutants, and nutrients through the uppermost layer of the subsoil: the unsaturated zone.

The unsaturated zone of the subsoil

The unsaturated zone is defined as the space that extends from the earth’s surface to the water-saturated zone saturated, occupied by pockets of groundwater. This layer can vary from a few centimeters to several meters, depending on the location, and its complex shape and structure make it a real challenge to study.

 

In the field of hydrology, a zone is said to be saturated when all the pore space inthe rocks is completely filled with water, while the unsaturated zone has spaces occupied by water and others occupied by air. Furthermore, in the upper layer of the unsaturated zone, biological activity by microorganisms is very common.

This area is key to understanding the climatic and hydrological dynamics that keep ecosystems functioning properly and sustain human activity. In fact, agriculture and livestock farming depend on it, homes are built on it, and all land transportation routes are located there.

“In the unsaturated zone, rainwater infiltrates into the groundwater below, acting as a physical-chemical filter and serving as a barrier against aquifer contamination”, explains IDAEA researcher Tomás Aquino.

The unsaturated zone is highly complex

Like all underground systems, the unsaturated zone is highly heterogeneous. There is significant variability in its structure, thickness, and composition, whether observed on a millimetre scale or at the level of metres or kilometres.

“Our current knowledge about this area is very limited. This makes it extremely difficult to predict key parameters of the water-soil system, such as the composition of the filtered water, the time it takes to infiltrate, or the volume of flow that ultimately reaches the deeper layers”, says Aquino.

Another challenge in studying this intermediate zone is the presence of air. Air pockets found between stones, rocks, roots, and other soil components influence water flow. Additionaly, most current studies are based on laboratory experiments, where researchers establish controlled conditions, yielding physical-chemical reaction rates that do not necessarily reflect real-world processes.

This knowledge gap means that existing research is insufficient for a comprehensive understanding of these processes.

Uplift Project

Thanks to €1.5 million in funding from the European Research Council (ERC), the Uplift project will have 5 years to develop models capable of accurately predicting the flow of water, pollutants, and nutrients through the unsaturated zone.

The main objective is to develop stochastic, or probabilistic, methods that can predict large-scale behaviour with maximum accuracy. Given the extreme complexity of the unsaturated zone, it is practically impossible to determine processes at the micrometre or millimetre scale. However, by drawing from studies conducted in the saturated zone, researchers can use statistical methods to analyse the structure of the medium and make reliable predictions at the field scale (metres to kilometres).

“Although we do not know in detail what happens at the micrometre and millimetre scale due to the high heterogeneity of the environment, these methods allow us to make highly accurate predictions at larger scales”, explains Tomás Aquino.

The project is structured into two main areas: (1) a theoretical component, where the team of scientists will develop mathematical models; (2) an implementation component, involving both small and large-scale numerical simulations. The project benefits from key collaborations that will provide experimental data to validate these models both in the field and in the laboratory. IDAEA-CSIC’s collaboration with other European institutions is crucial; specifically, the University of Rennes and the ETH Zurich will test the models in laboratory settings, while the Vallcebre Research Basins Service of IDAEA-CSIC, which holds long-term real hydrological data will enable in situ validation.

“The true strengh of this project lies in developing models capable of predicting real-world phenomena. We will achieve this by understanding the physical processes of the unsaturated zone and the statistical characteristics that define it, allowing us to determine the model parameters and make them more accurately reflect reality,” concludes Aquino.

 

The key, therefore, is to identify the simplest variables or characteristics of the environment that enable a more accurate prediction of what happens in the soil at a real scale. In this way, a model can be developed where, by indicating the characteristics of a specific space (e.g. type of soil, geology, flow of water that circulates, etc.) it can more accurately predict what will happen to a contaminant or nutrient that infiltratesthrough this medium into the groundwater beneath.