Appendix 4: Indicators of Wetland Hydrology, Plants and Soils

INDICATORS OF HYDROLOGY

The following hydrologic indicators can be assessed quickly in the field. Although some are not necessarily indicative of hydrologic events during the growing season or in wetlands alone, they do provide evidence that inundation or soil saturation have occurred at some time. One should use good professional judgment in deciding whether the hydrologic indicators demonstrate that the wetland hydrology criterion has been satisfied. When considering these indicators, it is important to be aware of recent extreme flooding events and heavy rainfall periods that could cause low-lying nonwetlands to exhibit some of these signs. It is, therefore, best to avoid, if possible, field inspections during and immediately after these events. If not possible, then these events must be considered in making a wetland determination. Also, remember that hydrology varies seasonally and annually as well as daily, and that at significant times of the year (e.g. late summer for most of the country) the water tables are at their lowest points. At these low water periods, signs of soil saturation and flooding may be difficult to find in many wetlands.

1). Visual observation of inundation - The most obvious and revealing hydrologic indicator may be simply observing the areal extent of inundation. However, both seasonal conditions and recent weather conditions should be considered when observing an area because they can affect whether surface water is present on a nonwetland site.

2). Visual observation of soil saturation - In some cases, saturated soils are obvious, since the ground surface is soggy or mucky under foot. In many cases, however, examination of this indicator requires digging a hole to a depth of 18 inches and observing the level at which water stands in the hole after sufficient time has been allowed for water to drain into the hole. The required time will vary depending on soil texture. Saturated soils may also be detected by a "squeeze test," which involves taking a soil sample within 18 inches (actual depth depends on soil permeability) and squeezing the sample. If free water can be extracted from the soil sample (indicating soil saturation), both the season of the year and the preceding weather conditions should be considered.

3). Oxidized channels (rhizospheres) associated with living roots and rhizomes - Some plants are able to survive saturated soil conditions (i.e., a reducing environment) because they can transport oxygen to their root zone. Look for iron oxide concentrations (orangish or reddish brown in color) forming along the channels of living roots and rhizomes as evidence of soil saturation (anaerobic conditions) for a significant period during the growing season.

4). Water marks - Water marks are found most commonly on woody vegetation but may also be observed on other vegetation. They often occur as stains on bark or other fixed objects (e.g., bridge pillars, buildings, and fences). When several water marks are present, the highest usually reflects the maximum extent of recent inundation.

5). Drift lines - This indicator is typically found adjacent to streams or other sources of water flow in wetlands and often occurs in tidal marshes. Evidence consists of deposition of debris in a line on the wetland surface or debris entangled in above-ground vegetation or other fixed objects. Debris usually consists of remnants of vegetation (branches, stems, and leaves), sediment, litter, and other water-borne materials deposited more or less parallel to the direction of water flow. Drift lines provide an indication of the minimum portion of the area inundated during a flooding event; the maximum level of inundation is generally at a higher elevation than that indicated by a drift line.

6). Water-borne sediment deposits - Plants and other vertical objects often have thin layers, coatings, or depositions of mineral or organic matter on them after inundation. This evidence may remain for a considerable period before it is removed by precipitation or subsequent inundation. Sediment deposition on vegetation and other objects provides an indication of the minimum inundation level. When sediments are primarily organic (e.g., fine organic material and algae), the detritus may become encrusted on or slightly above the soil surface after dewatering occurs.

7). Water-stained leaves - Forested wetlands that are inundated earlier in the year will frequently have water-stained leaves on the forest floor. These leaves are generally grayish or blackish in appearance, darkened from being underwater for significant periods.

8). Surface scoured areas - Surface scouring occurs along floodplains where overbank flooding erodes sediments (e.g., at the bases of trees). The absence of leaf litter from the soil surface is also sometimes an indication of surface scouring. Forested wetlands that contain standing waters for relatively long duration will occasionally have areas of bare or essentially bare soil, sometimes associated with local depressions.

9). Wetland drainage patterns - Many wetlands (e.g., tidal marshes and floodplain wetlands) have characteristic meandering or braided drainage patterns that are readily recognized in the field or on aerial photographs and occasionally on topographic maps. (CAUTION: Drainage patterns also occur in upland areas after periods of considerable precipitation; therefore, topographic position also must be considered when applying this indicator.)

10). Morphological plant adaptations - Many plants growing in wetlands have developed morphological adaptations in response to inundation or soil saturation. Examples include pneumatophores, buttressed tree trunks, multiple trunks, adventitious roots, shallow root systems, floating stems, floating leaves, polymorphic leaves, hypertrophied lenticels, inflated leaves, stems or roots, and aerenchyma (air-filled) tissue in roots and stems. As long as there is no evidence of significant hydrologic modification, these adaptations can be used as hydrologic indicators. Moreover, when these features are observed in young plants, they provide good evidence that recent wetland hydrology exists.

INDICATORS OF WETLAND PLANTS

There are hundreds of plant species that can grow and survive in aquatic environments. The identification of many of these species requires technical training in botany and related fields. However, there are some obvious plant species that are useful for making initial decisions that wetlands may be present on a given site. The classification system of the USFWS uses vegetative life forms as the primary means to categorize wetland types. Familiarity with the life forms of hydrophytes is a useful field tool. Brief descriptions of life forms and other wetland plant indicators are listed below:

submergent - hydrophytes that require complete immersion, and are generally rooted in the bottom; require stable water levels, and most require relatively clear, unpolluted waters; examples include - pondweeds, wild celery, elodea, water milfoil, and fanwort.

floating - hydrophytes that are either free-floating on the surface (duckweed) or rooted in the bottom with major leaves floating on the surface; water levels can vary somewhat, but must be sufficiently deep during the growing season; water quality also can vary as they are more tolerant of nutrient loads than submergent species; examples include - yellow pond lily, water lily, and watershield.

emergent - rooted hydrophytes where most of the plant material is above the water surface; water levels must fluctuate for proper growth and seed germination (usually during drawdown in late summer); both persistent species (cattails, sedges, some rushes) and non-persistent species (burreed, arrowhead, pickerel weed) occur with the persistent types remaining upright and robust after frost and death in the fall.

herbs and forbs – broad-leaved herbaceous plants that typically grow either in the shallow water edges of wetlands, ponds, and streams, or in the drier areas of wetlands; examples include sunflowers, jewelweed, mints, and cardinal flower.

vine – a woody stemmed plant that typically grows on other plants or objects to obtain support; examples include grapes and poison ivy.

shrub – woody hydrophytes that usually prefer seasonally flooded conditions; defined by USFWS as plants less than 20 feet tall with single or multiple stems; species can be broad-leaved deciduous, or broad-leaved evergreen; examples include dogwoods, viburnums, and bog shrubs like leather leaf.

tree – woody hydrophytes that dominate forested wetlands; defined by USFWS as greater than 20 feet tall; species can be any combination of broad- or narrow-leaved, and/or deciduous or evergreen; examples include willows, green and black ash, pin and swamp white oak, black spruce, and most commonly, red maple.

Other plants, such as ferns, mosses, and algae commonly occur in wetlands, but are usually harder to identify with certainty. Plants have been categorized as to their likelihood of being found growing in wetlands by botanical experts brought together by the USFWS. The following conventions are used in the wetland plant lists: degree of wetland dependence according to Reed (1988) and Tiner (1988); OBL = obligate (>99% occurrence in wetlands), FACW = facultative wet (67-99%), FAC = facultative (34-66%), FACU = facultative upland (1-33%), UPL = upland (<1%).

According to the federal jurisdictional manual, an area is considered wetland when the dominant plants (in terms of cover, number of stems, or visual estimate) are facultative or wetter types. That is, the prevalent vegetation has been positively identified such that the indicator status of these dominant species can be determined from the accepted USFWS plant lists (http://www.nwi.fws.gov/ecology.htm), and that there is more coverage by facultative, facultative wet, or obligate wet species than others preferring drier conditions. This determination requires strict adherence to the manual’s criteria, and positive identification of the plants in question.

There are other characteristics and structural adaptations found on individual plants that indicate they have been exposed to saturated or flooded conditions over a long period of time (repeated time periods during the growing season, usually 7 continuous days or more).

Buttressed (swollen) tree trunks
Multiple trunks
Pneumatophores ("knees")
Adventitious roots (arising from stem above ground)
Shallow roots (often exposed at the surface)
Hypertrophied lenticels (larger than normal "bumps" on the stems)
Aerenchyma (air-filled tissue) in roots and stems
Polymorphic leaves (many or unusual shapes)

This collective information is used to identify and delineate jurisdictional wetlands. If any of these indicators appear to dominate a particular site, or portion of a site, then it is likely that wetlands are present. Experienced personnel that are familiar with wetland delineation methods should be called in to make a jurisdictional determination, and to delineate the boundaries of the wetland, if present.

INDICATORS OF WETLAND SOILS

There are many indicators that may be used to determine whether or not wetland soils are present on a given site. Any of these indicators may be used as the basis for a positive determination that wetland soils are present. The indicators presented below may be useful for quick field identification of wetland soils, but a soils scientist or wetland scientist should perform jurisdictional determinations or detailed field studies.

1. Hydric soils – A hydric soil is a soil that is saturated, flooded or ponded long enough during the growing season to develop anaerobic conditions in the upper part. Hydric soils are defined locally by the Soil Conservation Service, but a field determination must be made to be certain.
2. Organic soils – A soil is classified as an organic soil if: (a) more than half of the upper 80 cm (32 in.) of soil is composed of organic material; or (b) organic soil material of any thickness rests on bedrock. Organic soils are saturated with water for long periods and are commonly called peat or mucks. These types of soils make poor building sites because they are characteristically wet and unstable.
3. Soil gleying – Gleyed soils are developed under conditions of poor drainage resulting in reduction of iron and other elements which produces gray soil colors. The anaerobic conditions that occur in "water-logged" soils result in the predominance of reduction processes. Iron is one of the most abundant elements in soils. Under anaerobic conditions, iron is converted from the oxidized (ferric) state to the reduced (ferrous) state and thereby produces the bluish, greenish, or grayish colors associated with the gleying effect. Soils gleyed immediately below the surface layer give an indication of saturation and/or inundation for long periods and are considered to be wetland soils.
4. Mottles with a chroma of 2 or less – Soil color is the most widely used indicator under normal field conditions. Mottled means that the soil is marked with spots of contrasting color. If a soil layer has a matrix color of gray and a few spots of red and brown, then the spots are referred to as mottles. Chroma refers to the strength (departure from neutral) of a color, and value refers to lightness. Soils that have mottles, and with chromas of 2 or less are generally saturated for some time during the growing season. Wetland or hydric soils should have a dominant matrix with a chroma of 2 or less a few inches below the surface. Munsell color charts are used to rank soil chroma and value.
5. Sulfidic material – Water-logged mineral or organic soils sometimes contain 0.75 percent or more of sulfur. These soils usually have sulfidic material near the mineral soil surface and are permanently saturated at or near the soil surface. This can be detected by the "rotten egg" or sulfur dioxide odor.

Source: Tiner 1998. Reprinted with permission.

Reprinted with permission.