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Identification of Wetlands

Onsite Identification: Corps of Engineers Methodology

Many federal, state, and local agencies, private organizations, and landowners need to identify or delineate the boundaries of wetlands for a variety of purposes. Each agency may be required to use one or more federal, state, or local laws or guidelines defining wetlands in specific ways. For example, the U.S. Army Corps of Engineers (Corps) administers the Section 404 program governing the discharge of dredge and fill material into waters in the U.S. as defined and guided by Section 404 of the Clean Water Act. The wetlands which fall within the Section 404 regulation are referred to as jurisdictional wetlands. The indicators of wetlands suggested by the Corps in their 1987 Manual for Delineation of Wetlands, (US ACOE 1987), are used as the basis for determining the presence of a wetland by most scientists and engineers. Other, broader, definitions of wetlands are generally used in addition to, or in place of, the Corps guidelines when the ecological aspects of wetlands are the focus. The U.S. Fish and Wildlife Service scientists and many other scientists, land use planners, and watershed or water quality managers, utilize the Cowardin system for more in-depth identification or classification of wetlands.

The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (formerly the Soil Conservation Service) will perform identification of wetlands on agricultural lands, as well as on non-agricultural lands within agricultural lands, or on non-agricultural lands, for landowners/operators who are USDA program participants (USEPA 1995). Natural Resources Conservation Service agents can determine the extent of wetlands for both the Swampbuster program and Section 404 at the same time using the definitions under Section 404 and the 1987 Manual. Formerly, Corps agents were required to make the Section 404 delineation. "Agricultural lands" are intensively used and managed cropland, hay land, pasture land, orchards, vineyards, and areas which support wetland crops (e.g. cranberries, rice, taro, and watercress) (USDA 1995).

The indicators of the presence of a wetland listed below are used in the Corps process of delineation provided in the 1987 Manual for Delineation of Wetlands (US ACOE 1987). A jurisdictional wetland requires three conditions (hydrophytes, hydrology, and hydric soils). The information given below is just basic information for onsite identification and should not be used for permitting or wetland delineation in a legal context. It is provided as a tool for watershed and water quality managers who want to assess whether an area is a wetland and thus may contribute to the watershed functionally. Onsite identification of the presence of a wetland will require familiarity with soil science and plant identification.

Wetland Indicators for Delineation (based on the 1987 Manual
(US ACOE 1987))

The indicators of the presence of a wetland are hydrophytic vegetation (plant life growing in water, soil, or on a substrate that is periodically deficient in oxygen due to excess water), presence of water, and hydric soils (soils saturated, flooded, or ponded, long enough during the growing season to develop anaerobic conditions in the upper profile). Observations of field indicators are used to determine whether the criteria are satisfied since the criteria alone may not be enough to document presence of a wetland. In particular, flooding or saturated soil conditions may occur for only a short time during the year, and generally not when delineators are present. For an ecological determination of the presence of a wetland, all that may be required is the presence of hydrophytic vegetation that require flooded or saturated conditions for survival. Such vegetation is outcompeted by upland species when wetlands are drained.


Hydrophytic vegetation

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Photo courtesy of
USDA NRCS

Photo courtesy of
US Army Corps of Engineers

Photo courtesy of
USDA NRCS

Criteria for a wetland: more than 50% of the composition of the dominant species (largest relative basal area (trees), greatest height (woody understory), number of stems (vines) or greatest areal cover (herbaceous understory)) from all strata (overstory, understory, woody vines, ground cover/herbaceous understory), must be obligate wetland (OBL) species, facultative wetland species (FACW), and/or facultative (FAC) species.

Field Indicators for hydrophytic vegetation

If obligate species comprise all dominant species in the community and there has been no recent significant hydroperiod alteration, soils and hydrology need not be determined for ecological determination of wetland presence.

Obligate and facultative wetland species are the most reliable indicators of the presence of a wetland. Since OBL species only occur in wetlands, their presence signifies that the area is a wetland. FACW species are less reliable, however, they do occur most often in wetlands (67-99%) than in uplands. A community dominated by OBL or by OBL and FACW should always be a wetland unless the area's hydrology has been significantly altered by human activity or other impacts.

If an area has FAC species but still greater than 10% areal cover of OBL species, the presence of a wetlands is indicated (Tiner 1993).

The U.S. Fish and Wildlife Service has listings of wetland plant species by region available on the WWW at URL HTTP://www.nwi.fws.gov/Ecology.html


Hydrology

Wetlands require permanent or periodic inundation or soil saturation at the surface for a week or more during the growing season to be a wetland ecologically as well as for jurisdictional purposes. These conditions create an anaerobic environment which affects the plants and soil. Hydrology is not as useful for wetland identification as the use of vegetation and soil characteristics since many wetlands are dry for much of the year. Hydrology is a feature of the regulatory determination of "jurisdictional wetlands" but is considered "technically flawed" by experts in the field of delineation who recommend that only vegetation and soil characteristics be used (Tiner 1993; Day et al. 1993).

However, if obligate species comprise all dominants in the community and there has been no recent significant hydroperiod alteration, the hydrology characteristic is fulfilled for jurisdictional wetland delineation even if no water is present.

Field indicators of wetland hydrology:

  1. visual observation of inundation
  2. visual observation of soil saturation in 18" hole to 12" depth
  3. watermarks (stains on bark or other fixed objects)
  4. water-borne debris deposition, particularly in aboveground vegetation
  5. water-borne sediment deposits on plants and other vertical objects
  6. drainage patterns within wetlands, including scouring
  7. water stained (blackened or grey) leaves
Other indicators of wetland hydrology are morphological adaptations to flooded or saturated conditions (see below), and hydric soil characteristics.

Recorded data of soil inundation and saturation for a significant time (more than a week) during the growing season and aerial photographs displaying inundation are other useful information sources to determine hydrology.

Morphological adaptations to permanent or periodic inundation or
soil saturation and examples of species displaying adaptations
Adaptation                      Species
<hr>
Buttressed tree trunk                 Taxodium distichum (Bald cypress), 
(swollen bases)                          Nyssa (Gum)

Multiple trunks                          (Acer rubrum) Red maple

Pneumatophores (knees)           Taxodium distichum, Nyssa aquatica 
Stubby projections extending 
from the roots to heights above 
the average water level.

Adventitious Roots                    Plantanus occidentalis (Sycamore), Salix
Roots occurring on plant            (Willow), Ludwigia (Water primrose) 
stems and above soil surface.

Shallow roots (exposed)              Acer rubrum (Red maple)

Hypertrophied lenticels                Salix (Willows), Acer rubrum (Red maple)
Large lenticels, allowing 
greater gas exchange

Aerenchyma in roots and stems   Juncus spp. (Rush), Typha spp. (Cattails), 
spongy, air filled tissue                Cyperus spp. (Sedges)

Polymorphic leaves                     Sagittaria (Arrowheads),
Leaves that have different 
shapes depending on site conditions

Floating leaves                           White water lily,

Hydric soils

Hydric soils take time to form, and are formed from regular or constant water saturation or inundation. Hydric soils include:

1. All Histosols except Folists,

Histosols are organic soils (more than 50% of upper 32 inches by volume is organic) or any depth of organic material on bedrock; Folists are non hydric organic soils originating from excessive moisture in tropical and boreal mountains.

or,

2. Soils in Aquic suborders and Aquic subgroups that are:

  1. Somewhat poorly drained and water table <0.5 ft from the surface (>1 week during the growing season.
  2. Poorly drained or very poorly drained and have either:
    1. Water table <1 ft from the surface for (>1 week during the growing season if permeability (6 in/hr in all layers within 20 inches of the surface
    2. Water table < 1.5 ft from the surface for (>1 week during the growing season if permeability <6 in/hr in all layers within 20 inches of the surface.
    3. Soils that are ponded for long duration (or inundation by a single event for (7 days) during the growing season.
    4. Soils that are frequently flooded (> 50% probability of flooding in a given year) for long duration during the growing season.
Field indicators of hydric soils:

These are listed in the order in which they can be used to definitively indicate whether soils are hydric and the area is a wetland.

  1. Histosols (except Folists)*
  2. Histic epipedon *
  3. Sulfidic materials (H2S) in mineral soils emitting the smell of rotten eggs
  4. Aquic moisture regime (usually hydric soil) or peraquic moisture regime*
  5. Reducing soil conditions as indicated by:
    1. Gleyed soils (blueish or greenish gray) immediately below A horizon, matrix chroma (predominant color) less than or equal to 1 (using Munsell Soil Color Book)
    2. Bright mottles immediately below A horizon or 10 inches and/or matrix chroma of less than or equal to 2 (if soil has mottles; color determined with wet or moist soils)
    3. Iron (reddish brown) and/or manganese (black) concretions
*always hydric soils

NOTE: Color is not a reliable indicator in sandy or coarse textured soils.

Coarse-textured or sandy hydric soils:

  1. High organic matter content in the surface horizon. The mineral surface layer will appear darker than the mineral layer below it.
  2. Dark vertical streaking of subsurface horizons by organic matter movement as water table fluctuates.
  3. Wet Spodosols. Accumulation of organic matter 12 to 30 inches below the mineral surface.
Useful references for determining hydric soils are the USDA Soil Surveys and the USDA Hydric Soils List.

The Primary Indicators Method (PRIMET), developed by Ralph Tiner, U.S. Fish and Wildlife Service, is a technically sound, precise, practical, efficient, method of wetlands delineation requiring a single site inspection. It is based on the same information as is presented above but puts it into a series of questions. It is usable throughout most of the year and encompasses regional variation. PRIMET is a useful tool for watershed and water quality managers who want to get a sound but efficient assessment of whether an area is technically a wetland and thus may contribute to the watershed functionally. Wetlands Vol. 13, No. 1, 1993 p. 56.

Offsite Identification of Wetlands

Offsite identification of wetlands can be a useful screening tool to determine the possible existence of wetlands. However, on-site verification is necessary to establish the existence, size, shape, and type of wetlands. Some resources for offsite identification of wetlands include:

U.S. Geological Survey (USGS) Topographic Maps

These maps portray vegetation cover types, surface features, rivers, lakes, canals, submerged areas, and bogs. Specific terms are used. A marsh or swamp is characterized by saturated, not inundated, soil conditions in the root zone, with emergent herbaceous or floating vascular (aquatic bed) vegetation. A wet meadow is an example. A submerged marsh or swamp has inundated soil conditions with emergent herbaceous or floating vascular (aquatic bed) vegetation. An example is a cattail (Typha) marsh. A wooded swamp or marsh has saturated soil conditions with shrub (including sapling) or forest vegetation. A red maple (Acer rubrum) swamp is an example. A submerged wooded marsh or swamp, has inundated (ponded) soil conditions with shrub (including sapling) or forest vegetation. A bottomland hardwood forest with cypress (Taxodium) is an example. The term land subject to inundation indicates floodplain areas. Rice fields and cranberry bogs are often wetlands that have been manipulated by man. The USGS Topographic Maps allow historical evaluation of a site which can be useful for restoration purposes. Small wetlands, however, are often not included because of their size and the scale of the maps -- generally 1:24000 -- (1 inch = 610 meters).

National Wetlands Inventory

The National Wetlands Inventory (NWI) was initiated by the U.S. Fish and Wildlife Service in 1975 to characterize the extent of wetlands and open water in the United States. Under the Emergency Wetlands Resources Act of 1986, the Fish and Wildlife Service is required to map wetlands of the lower 48 states and to assess the nation's wetland resources every 10 years.

The maps are produced from high altitude aerial photographs at a scale of 1:600,000 and use U.S. Geological Survey Topographic Maps (USGS Topo Maps) as basemaps with the wetlands and deepwater systems as overlays. The Cowardin system specifically corresponds to the NWI maps. There is error inherent in the NWI maps beyond the normal human error involved in photointerpretation and mapmaking, since small wetlands are generally not distinguishable from the surrounding uplands at a scale of 1:600,000 and small wetlands may not have been mapped on the USGS Topo Maps. The National Wetlands Inventory maps are available in paper as well as digital format and magnetic tape in MOSS export, DLG3, Arc for workstations, and Arc/Info for PC.

USDA Soil Conservation Service Soil Surveys and Hydric Soils List

Soil surveys may be used to identify and delineate hydric soils, however accuracy of the maps is variable. The Soil Conservation Service is now called the Natural Resources Conservation Service.

The three types of maps described above may be used together to develop an estimate of the location and type of wetlands in a particular area.

Aerial photographs and satellite images may be used as well and are available in many formats and scales.

Some states have developed wetlands maps and mapping is ongoing in other states.

Source: (Kent 1994a)


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