Preferential flow of gas in soils

气体在土壤中移动，因为土壤是多孔介质，具有连通的孔隙。这种气体运动允许数十亿的生物，如植物、细菌和真菌呼吸和分解产物（如碳氢化合物）。这些活动产生的气体必须从土壤中排除到大气中，以避免毒性。气体和水一样，在土壤中运动不均匀。气体只通过土壤的一部分，称为“优先流动路径”，如果气体在整个土壤体积中移动，这种路径有利于气体更快地移动，这比用模型预测的要快。优先流是由各种大小的土壤非均质性引起的。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获系统的效率等。对土壤中气体的PF所知甚少。本研究的主要目的是了解和量化几种条件下（如冻结，潮湿，有大孔隙）土壤中气体的PF。实验室试验将在重新包装的土壤柱和在现场观察到土壤异质性的大型单体上进行。将对单块石进行扫描（CT扫描仪，就像在医院一样），以三维方式描述土壤孔隙度，并将孔隙度结构与气体的PF相关联。该项目是提高对土壤中气体通量认识的重要一步。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.