Final answer:
The capillary fringe is the layer just above the water table and is a part of the zone of aeration. It's where both water from the saturated zone below and air from above meet, allowing for the expulsion of gases and improving water quality through the process of aeration.
Step-by-step explanation:
The capillary fringe sits directly above the water table and is part of the zone of aeration. The capillary fringe is the subsurface layer where water molecules are drawn upward from the water table by capillary action. This layer is above the fully saturated zone but is still influenced by the presence of groundwater below. In the capillary fringe, pore spaces in soil and rock contain both air and water, contributing to the aeration of the groundwater system. Below this is the saturated zone, where all pore spaces are filled with water.
In the process of aeration, air comes into contact with water, facilitating the exchange of gases and the removal of volatile substances. This process is essential for maintaining the quality of both groundwater and surface water. During aeration, unwanted gases such as hydrogen sulfide and ammonia can be expelled from the water, improving its odor and taste and making it safer for consumption and supporting aquatic life.