Identification 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.
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.
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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.
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
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:
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
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 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.
2. Soils in Aquic suborders and Aquic subgroups that are:
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.
NOTE: Color is not a reliable indicator in sandy or coarse textured soils.
Coarse-textured or sandy hydric soils:
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.
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.
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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