Water in the Unsaturated Zone

Abstract The soil profile immediately below the land surface and above the water table is called the unsaturated zone, where the pores contain both water and air. This zone differs from the saturated zone, where the pores are saturated with water. The unsaturated zone is sometimes called the vadose zone. The thickness of an unsaturated zone can range from zero (e.g., when a lake or marsh is at the surface) to hundreds of meters, as is common in arid regions. It is a zone of natural and human‐induced activity. It experiences physical phenomena such as thermodynamic interactions, transport processes of various kinds, and chemical reactions involving both natural and artificial substances. Several biological activities involving plant roots, rodents, worms, microbiota, and other organisms also take place in this zone. The zone is used for cultivating plants, constructing structures, and disposal of waste. To a large degree, the unsaturated zone controls the transmission of water to aquifers (water bearing strata), as well as to the land surface, to water on the surface, and to the atmosphere. It also acts as a filter as it removes undesirable substances before they reach and affect aquifers.