Preferential flow of gas in soils

气体在土壤中移动是因为土壤是具有连通孔隙的多孔介质。这种气体运动允许植物、细菌和真菌等数十亿生物呼吸和分解产物(例如碳氢化合物)。这些活动产生的气体必须从土壤中清除到大气中，以避免有毒。气体和水一样，不能在土壤中均匀地运动。气体只使用通过土壤一部分的路径，称为优先流动路径，这有利于气体的移动比模型预测的更快，如果气体将通过土壤体积。优势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集系统的效率等，但对土壤中气体的PF知之甚少。这项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。实验室实验将在重新填充的土柱上进行，并在田间观察到土壤非均质性的大型整体上进行。用CT扫描仪(如医院中的CT扫描仪)对土体进行扫描，在三维上描述土壤孔隙度，并将孔隙度结构与气体的Pf关联起来。该项目是提高对土壤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、氧化还原反应和土壤工程过程的效率有关的数据解释。

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.