Researchers often use two-dimensional (2D) experiments and computer models to study how water, air, and chemicals move and react in porous materials like soil and rock. However, these 2D approaches can give misleading results because they cannot fully capture the complex flow patterns that occur in real three-dimensional (3D) systems. This difference is especially important when the pores are not fully saturated with water, since the way water and air connect and create flow pathways is strongly influenced by the third dimension.

In this study, we used high-resolution 3D simulations to examine how mixing and chemical reactions occur in unsaturated porous media. We found two key results: (1) in 3D systems, the amount of reaction products peaks at intermediate water saturations, a behavior that does not appear in 2D models; and (2) the strong mixing effects often reported in 2D studies at low water saturations are much weaker in 3D. These differences show that the geometry and connectivity of phases in 3D is critical to how substances move and react underground.

Our findings demonstrate that relying on 2D studies can lead to incorrect predictions and emphasize the need for realistic 3D experiments to better understand subsurface flow and chemical reactions.