A critical mini-review on the low-field nuclear magnetic resonance investigation of pore coupling effects in near-surface environments

The assessment and monitoring of groundwater resources is increasing importance to ensure the continuous supply fresh water for human activity endangered ecosystems. These include fully saturated aquifers, in unsaturated soil, trapped as rock moisture weathered bedrocks. Low-field nuclear magnetic resonance (NMR) a method with unique sensitivity pore water, it based on magnetization relaxation behavior spin moment hydrogen atoms forming molecules. It cost-effective minimally-invasive technology that can help characterize structures distribution transport different types subsurface materials. However, interpretation NMR data from samples complex bimodal or multimodal porous geometries requires consideration coupling effects. A pore-coupled system presents significant exchange between macro- micropores within measurement time, making independent characterization each environment difficult. Developing better understanding great accurate estimation hydrogeological parameters data. This mini-review state-of-art research exploring two factors controlling coupling: surface geochemistry network connectivity, summarizes existing experimental numerical modeling approaches have been used study discusses effects partially conditions. At end this review, we outline major knowledge gaps highlight needs vadose zone.