What characterizes a wetland?

A wetland is characterized by its unique hydrological conditions, which include having soil that is saturated with water for part of the year. This saturation leads to distinct soil types and supports specific vegetation adapted to such conditions, such as cattails and reeds. Wetlands play a vital role in ecosystems; they act as natural water filters, provide habitat for numerous species, and help in flood control. The presence of saturated soil distinguishes wetlands from other types of environments, as it creates a unique ecosystem that relies on this intermittent water availability for its biological diversity.

The other options do not accurately reflect the characteristics of wetlands. For instance, wetlands are not devoid of vegetation; in fact, they often have rich plant life. Furthermore, they are not always underwater; rather, they may experience seasonal variations in water levels. Lastly, wetlands are not confined to desert environments, which typically have dry soil and lack the necessary conditions for wetland ecosystems to thrive.