Wetlands

When did wetlands become more strictly defined?

mid-twentieth century

Why did wetlands need to have precise definitions?

Their value began to be recognized in the 1970s which resulted in this need.

Are wetlands terrestrial or aquatic systems?

While sharing components of both, they are technically neither

What are the distinguishing features of wetlands?

1. Hydrology

2. Physiochemical Environment (soil conditions)

3. Biota

Hydrology

wetlands are distinguished by the presence of water, either at the surface or within the root zone

Physiochemical environment

Wetlands often have unique soil conditions that differ from adjacent uplands (i.e., hydric soils). This creates anaerobic conditions, which supports biota adapted to wet environments

Biota

Wetlands support biota such as vegetation adapted to wet conditions (hydrophytes), and are characterized by an absence of flood-intolerant biota. contains both obligate (OBL) and facultative (FACW, FAC) species.

Obligate wetland (OBL) vegetation

Almost always occurs in wetlands under natural conditions (>99%)

Facultative wetland (FACW) vegetation

Usually occurs in wetlands (67%-99%), but is occasionally found in non-wetlands (1%-33%)

Facultative (FAC) vegetation

Equally likely to occur in wetlands non-wetlands (34%-66%)

(I)

Hydrology (water level, flow, frequency, etc)

(II)

Physiochemical environment (soil, chemistry, etc)

(III)

Biota (vegetation, animals, and microbes)

(IV)

geomorphology (elevation, slope, basin shape, etc)

(V)

climate (precipitation, temp, evapotranspiration)

Difficulties defining wetlands

1. Hydrologic variability (daily, seasonally, yearly)

2. Wetlands are ecotones

3. Wetland species’ tolerance varies (obligate and facultative)

4. Wetlands exist in diverse landscape contexts

5. Human influence

Hydrologic variability

the depth and duration of flooding can vary among different wetlands and within any given wetland daily (e.g., tidal marsh), within a year (e.g., swamp, fen, vernal pool, etc.), or among years

Wetlands are ecotones

boundaries around wetlands are arbitrary, gradients are only occasionally sharp and obvious

Wetland species’ tolerance varies

some species in wetlands require saturated conditions (obligate), which some only tolerate saturated conditions and can live in non-saturated substrates (facultative)

Wetlands exist in diverse landscape contexts

they vary widely in size, landscape location, and connectivity (e.g., a coastal marsh that takes up thousands of acres vs. an isolated mountain fen that’s 10 square meters)

Human influence

human modifications can obscure indicators of naturally-occurring wetlands (e.g., agriculture, dams, etc.)

Swamp

a wetland dominated by trees or shrubs

Marsh

a frequently or continuously flooded wetland characterized by emergent herbaceous vegetation (no trees)

Bog

a type of peat-accumulating wetlands primarily fed by precipitation (i.e., little inflow or outflow of groundwater or surface water)

Fen

a type of peatland in which there is some degree of groundwater influence and can support woody and/or herbaceous vegetation

Two groups of wetland definitions

scientists: definitions need to facilitate classification and research

regulators: definitions provide legally-binding frameworks for management

Scientific definition A. Circular 39 (USFWS) ( Shaw and Fredine1956)

waterfowl habitat, massive inventory and delineation effort, 20 basic types of wetlands

-shallow and sometimes temporary to intermittent waters
-they are referred to by such names as marshes, swamps, bogs,
wet meadows, etc.
-usually with emergent vegetation

Scientific definition B. USFWS: Cowardin et al.

states wetlands must have one or more of the following: land that support hydrophytes, predominantly undrained hydric soil substrate, saturated with water or covered by shallow water at some time during growing season

Legal definition A. US Army Corps of Engineers via Clean Water Act (1977)

Wetlands means areas that are inundated or saturated by surface or ground water that, under normal circumstances, support lots of vegetation typically adapted for life in saturated soils.

1975 version: vegetation that requires saturated soil conditions, excluded facultative biota

No specific reference to hydric soils, only saturated soil conditions. Over the years the rules have shifted, but the 1977 version remains the most used legal definition

Legal definition B. Food Security Act: Swampbuster Provision 1985

Wetland means:

A. has a predominance of hydric soils

B. inundated or saturated by surface or groundwater and has hydrophytic vegetation

C. support a prevalence of such vegetation under normal conditions

The swampbuster provisions…

Notably excludes wetlands in Alaska. Forestry and ag activities were exempt before swampbuster provision (USDA was still providing subsidies for wetland drainage in 1985). Updated CWA to include a soils component.

Legal definition C. Jurisdictional Wetlands

wetlands that fall under Section 404 of the CWA (hydrology and hydrophytes) or the swampbuster provision of the FSA (hydric soils)

1. Boundaries are important: wetland delineation identifies jurisdictional wetland boundaries. Hydrology, hydric soils, and hydrophytic vegetation as key components.

2. Individual US states may have more specific jurisdictional wetland requirements (e.g., NY State Freshwater Wetlands Act)

Choice of Definitions

1. Precision varies: the definition of wetlands depends on the objectives and the field of interest of the user

2. Truly accurate wetland definitions require a fundamental understanding of wetland ecology and its unique processes!