Wetlands: Definitions, Types, Processes, and Conservation

Wetland definitions and terminology

Wetlands are distinct semi-aquatic ecosystems where the ground is flooded or saturated with water—permanently, for years/decades, or seasonally—long enough to support aquatic plants. Flooding creates oxygen-poor (anoxic) soil conditions that shape wetland soils, vegetation, and ecological processes. Wetlands also function as transitional zones (ecotones) between terrestrial and aquatic environments, and they are commonly defined using hydrology (water level and duration) along with characteristic hydric soils and hydrophytes. Terminology and formal definitions vary by purpose. The Ramsar Convention defines wetlands broadly to include marshes, fens, peatlands, and water bodies (natural or artificial; permanent or temporary; static or flowing; freshwater, brackish, or salt), including certain shallow marine areas. In the United States, regulatory definitions similarly emphasize areas inundated or saturated by surface or groundwater at frequencies and durations that support vegetation adapted to saturated soil conditions. Ecological definitions also stress how inundation produces soils dominated by anaerobic and aerobic processes, forcing biota—especially rooted plants—to adapt to flooding. Wetland types and names are often based on dominant vegetation and water source. Common categories include marshes, swamps, bogs, and fens (with bogs and fens as peatland types), plus additional sub-types such as mangrove forests and vernal pools. Water can be tidal or non-tidal, and wetlands may be freshwater, brackish, saline, or alkaline. Regional names (e.g., prairie potholes, pocosins, turloughs, billabongs) reflect local terminology for particular wetland systems, while locations can be described by temperature zone and precipitation regime.

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Technical criteria: hydrology and hydric soils

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