Modeling Water, Heat, and Nitrate Dynamics in the VadoseZone: A Case Study of the Beauce Aquifer (Orleans, France)

The Unsaturated Zone (UZ), the portion between the soil surface and the groundwater table, has a significant impact on subsurface water resources. This zone controls water movement from the soil surface to the aquifer and acts as a natural filter, purifying groundwater by removing or transforming solutes as water moves from the surface towards the water table. A thorough understanding of the processes occurring within the UZ is essential for sustainable land and water resource management, especially in the context of climate change and increasing agricultural demands. This study is conducted on a representative scale of the Beauce aquifer and is leverage extensive data from the Observatory of transfers in the Vadose Zone (O-ZNS) in Villamblain, France. The observatory’s unique setup, which includes a 20-meter deep well with a diameter of 4 meters, multiple boreholes, and innovative environmental sensors, provides high-resolution 3D measurements of fluid flow and heat/mass transfer processes.
The complex and coupled processes governing mass and heat transfer in the UZ determine the fate of pollutants and impact groundwater quality. In this study, a coupled model of water, heat, and nitrate transfer in the UZ of the Beauce aquifer is developed to assess the impact of climatic variations and agricultural practices on groundwater responses. Hydraulic properties, meteorological data, water table levels, and agricultural data—including crop types, fertilizer application rates, and pesticide usage reported by local farmers—are used as model inputs for the period from 2021 to 2025.

Numerical simulations are validated against volumetric water content measurements at the well level and against observed water content and temperature profiles in a 2-meterdeep soil pit. The model predictions showed in general good agreement with experimental observations, confirming its reliability. Various scenarios are explored by altering meteorological inputs and nitrogen fertilization rates to evaluate their impacts on groundwater responses. The results demonstrated diverse behaviors of the UZ, highlighting the sensitivity of groundwater quality to agricultural practices and climatic conditions.

The outcomes of this research provide valuable insights into the mechanisms governing the heat and mass transfer through the UZ of carbonate aquifers, contributing to more accurate predictions of groundwater responses to intensive agriculture, ecological and climatic changes.