Understanding Wetlands: Types, Processes, and Policy

Wetland definitions and terminology

A wetland is a distinct semi-aquatic ecosystem where the ground is flooded or saturated with water—permanently, for years/decades, or seasonally—so that waterlogged, oxygen-poor (anoxic) soil processes occur. Wetlands form a transition zone between terrestrial and aquatic systems, and their vegetation is adapted to these waterlogged conditions. A simplified definition is land that is usually saturated with water, while more precise definitions emphasize water covering the soil or being present at/near the surface for enough time to support aquatic plants. Terminology and regulatory usage distinguish wetlands by hydrology (water level, flooding duration, and water table position) and by the types of plants and soils present. For example, the Ramsar Convention defines wetlands broadly to include marshes, fens, peatlands, and water bodies (natural or artificial; permanent or temporary; fresh, brackish, or salt), including certain shallow marine areas. In the United States, wetlands are defined as areas inundated or saturated by surface or ground water with sufficient frequency and duration to support vegetation adapted to saturated soil conditions. Wetlands are also described ecologically as systems where inundation produces soils with anaerobic and aerobic processes that force rooted organisms to adapt to flooding.

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Technical and regulatory wetland definitions

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