Preferential flow of gas in soils

气体在土壤中移动，因为土壤是具有连通孔隙的多孔介质。这种气体运动允许数十亿生物（例如植物、细菌和真菌）呼吸并分解产物（例如碳氢化合物）。这些活动产生的气体必须从土壤中消除到大气中，以避免毒性。气体和水一样，在土壤中不是均匀移动的。气体只通过一部分土壤的路径，称为“优先流动路径”，这有利于气体的移动速度比模型预测的更快，如果气体将通过大量土壤体积移动。优先流是由各种大小的土壤非均匀性引起的。PF影响植物和微生物的生长，化学反应，土壤净化系统和垃圾填埋场气体捕集系统的效率等。本研究的主要目的是了解和量化的PF气体在土壤中的几种条件下（如冻结，潮湿，与大孔隙）。实验室实验将在重新填充的土柱和大型整料上进行，其中土壤异质性与野外观察到的相同。将对整料进行扫描（如医院中的CT扫描仪），以三维描述土壤孔隙度，并将孔隙度结构与气体PF相关联。该项目是提高对土壤中气体通量的认识的重要一步。它将有助于开发更合适的模型，土壤管理和净化，改善与植物，微生物，氧化还原反应有关的数据解释，以及土壤工程过程的效率。

Gas move in soils because soils are porous media with connected pores. This gas movement allows billions of organisms such as plants, bacteria, and fungus to breathe and decompose products (e.g. hydrocarbons). These activities generate gases that must be eliminated from the soil toward the atmosphere to avoid toxicity. Gases, as for water, do not homogeneously move in soils. Gases use pathways through only a portion of the soil, called 'preferential flow pathways', which favour faster movement of gases than it would be predicted with models if the gases would be moving through the bulk soil volume. Preferential flow is caused by soil heterogeneities of all sizes. PF affects the growth of plants and micro-organisms, chemical-reactions, efficiency of soil decontamination systems and gas capturing systems in landfills, etc. Very little is known on PF of gases in soils. The main objective of this research is to understand and quantify PF of gas in soils under several conditions (e.g. frozen, wet, with macropores). Laboratory experiments will be conducted on repacked soil columns and on large monoliths in which soil heterogeneity is as observed in the field. The monoliths will be scanned (CT scanner as in hospitals) to describe soil porosity in three dimensions and correlate the porosity structure with PF of gas. This project is an important step in improving knowledge on gas flux in soil. It will help in developing more appropriate models, soil management and decontamination, improving data interpretation relative to plant, microbes, oxydo-reduction reactions, and efficiency of engineering processes in soils.