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Wetland Delineation- Hydrologic Indicators

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It is important to read the first paragraph of section 62-340.500, F.A.C. as it qualifies the use of the hydrologic indicators with reasonable scientific judgement (see Delineation Manual Introduction). Reasonable scientific judgement involves consideration of the conditions causing the indicators. The presence of hydrologic indicators may not provide any information on the normalcy of the event or series of events causing the conditions. Every effort should be made to acquire detailed knowledge about the site prior to considering factors which are directly caused by the immediate presence of water. The lack of certain or specific hydrologic indicators at a site should not be viewed as negative evidence when other indicators are present. It is the total weight of the evidence of wetland conditions on site, provided by the indicators present that, once subjected to reasonable scientific judgement, is used or rejected in establishing the wetland boundary. The following thirteen hydrologic indicators are listed in the rule.

(1) Algal mats are the presence or remains of nonvascular plant material which develops during periods of inundation and persists after the surface water has receded. Algal mats are important indicators of inundation when the vegetation and soil has been altered. In addition, seasonally flooded natural areas such as depression marsh, interdunal swale, rocklands in the Florida Keys and extensive areas of marl/swale of the Everglades may have extensive algal mats as the only hydrologic indicator present. In southwest Florida, algae mats are one of the most important wetland indicators because of the lack of organic accumulation in many of the seasonally inundated communities. Algal mats are often associated with aufwuchs and water marks. The degree to which this indicator is expressed on a site is best interpreted when the rainfall history of the area is known.

(2) Aquatic mosses or liverworts on trees or substrates. Mosses and liverworts are in a group of plants collectively called bryophytes. They lack true roots and leaves and are generally found in shaded, moist environments. Look for epiphytic or epipteric mosses and liverworts along rivers, streams, bayous, sloughs and strands as they typically occur in shaded, forested floodplains that experience prolonged, seasonal inundation. After water levels have fallen, they will appear as a dark greenish-brown "shaggy" growth, suspended on the bark of trees and the surface of rocks. Typically encountered mosses include: Brachelymaspp., Dichelyma capillaceum, Fissidensdebilis, Fissidens manateensis, Fontinalis spp., Hygroamblystegium tenax, Leptodictyum riparium, Sciaromnium lescurii, and Sphagnum spp.; liverworts include: Porella pinnata. Identification of dried bryophytes is aided by a hand lens and the application of water to the dried plant body. Two taxonomic references of use are: Mosses of Florida by Ruth Schornherst Breen, 1963 and Mosses of the Gulf South by William Dean Reese, 1984.

(3) Aquatic plants. Aquatic plants are defined in section 62-340.200, F.A.C. as "plants which typically float on water or require water for its entire structural support, or which will desiccate outside of water." Aquatic plants naturally grow in areas where inundation is permanent or nearly so. The presence of aquatic plants at a site not presently inundated by water is an excellent indicator that the normal condition at the site is much wetter or, in the case of floating plants, that the site experiences periodic flooding by an adjacent surface waterbody. Look for evidence of aquatic plants in seasonally fluctuating water bodies. Typical floating aquatics include such genera as: Riccia, Ricciocarpus, Azolla, Salvinia, Pistia, Echhinoria, Lemna, Spirodela, Wolffia, and Wolffiella in seasonally flooded, shallow lakes and ponds or surrounding floodplain forests. An aid to the identification of the previously mentioned plants can be found in R. K. Godfrey, Aquatic and Wetland Plants of Southeastern U. S., 1979 and floras published for a particular area of the state. Water lines and aufwuchs are often also associated with a seasonal drawdown of water bodies.

(4) Aufwuchs is the presence or remains of the assemblage of sessile, attached or freeliving, nonvascular plants and invertebrate animals (including protozoans and fresh water sponges) which develop a community on inundated surfaces. Look for the presence of aufwuchs on branches, rocks and other objects that have been submerged. Aufwuchs are important indicators in seasonally inundated areas. They often appear as a crust-like growth, sometimes bleaching to white in sunlight during the dry seasons.

(5) Drift lines and rafted debris are vegetation, litter, and other natural or manmade material deposited in discrete lines or locations on the ground or against fixed objects, or entangled above the ground within or on fixed objects in a form and manner which indicates that the material was waterborne. This indicator should be used with caution to ensure that the drift lines or rafted debris represent usual and recurring events typical of inundation or saturation at a frequency and duration sufficient to meet the wetland definition of subsection 62-340.200(19), F.A.C. When debris has been carried by water and deposited in an area, especially an area foreign to the origin of the material, then the conditions contributing to the observations must be considered. For example, extreme events such as hurricanes and tropical storms may induce unusually high drift lines and rafted debris associated with a storm surge that would not be typical for a particular area. Look for drift lines in tidal areas, rivers and streams that regularly flood, or any wetland where high water deposits or arranges leaves and twigs in a distinguishable pattern. In evaluating rafted vegetative debris, be sure to consider only water-induced evidence.

(6) Elevated lichen lines. Lichens are a symbiotic association of a fungus and an alga. Typical lichen forms include crustose, foliose and fruticose. Crustose lichens are flattened and appressed like a film on the bark. Foliose lichens are flattened, thin and lobed. Fruticose lichens are highly branched, forming a shrubby, bushy structure of flattened or cylindrical branches. The crustose and foliose type of lichen are the most commonly encountered on the bark of trees. Lichen are not tolerant of inundation. When water routinely stands around the trunks of trees it abruptly limits the growth of lichens producing a distinct line. These are instructive as part of the information used in determining the ordinary or seasonal high water line for some types of wetlands and other water bodies. Many shallow swamps have a seasonal high water which does not result in prolonged inundation of the tree trunks. These wetlands exhibit inundation as the pooling of water over the swamp floor which is typically at a lower elevation than the base of the trees (see vegetated tussocks and hummocks). Lichen lines would not be anticipated in this type of wetland.

(7) Evidence of aquatic fauna. This indicator considers the presence or indications of the presence of animals which spend all or portions of their life cycle in water. Only those life stages which depend on being in or on water for daily survival are included in this indicator. Remember that some types of aquatic fauna are extremely motile and can move into non-wetland areas because of abnormal conditions such as prolonged flooding. Additionally, some adult aquatic beetles and bugs are capable of flight and readily leave the water during warm humid nights. It is not unusual to encounter these animals in uplands, especially if night lighting is present. Look for evidence in the cast skins of insect larva, especially dragonflies, on emergent vegetation, or remanent molluscan shells (bivalves and snail). Crayfish burrows are excellent hydrologic indicators but must be considered with care as they can occur outside areas defined as wetlands and may only be indicators of a seasonal high water table. When this is the case however, the burrows are, almost without exception, much more numerous on the wetland side of the boundary.

(8) Hydrologic data consists of reports, measurements, or direct observation of inundation or saturation which support the presence of water to an extent consistent with the provisions of the definition of wetlands and the criteria within the rule, including evidence of a

seasonal high water table at or above the surface according to methodologies set forth in Soil and Water Relationships of Florida's Ecological Communities (Florida Soil Conservation Staff 1992) available on the Wetland Delineation Publications page. These observations should

be used in conjunction with observations offered by local residents, published reports or data and other hydrologic indicators observed in the field. Provided that a site has not been extensively drained, county soil surveys are an excellent source for hydrological conditions typically associated with a specific map unit.

(9) Morphological plant adaptations are specialized structures or tissues produced by certain plants in response to inundation or saturation which normally are not observed when the plant has not been subject to conditions of inundation or saturation. These are often observed in the form of hydric adventitious roots and hypertrophied lenticels. Hydric adventitious roots are typically produced on the stem or trunk of certain plants, when inundated, as an alternative mechanism for aerobic respiration during a period of anoxia in the soil root zone. Once inundation subsides, these roots cease growth. Hydric adventitious roots are seldom observed rooted into soil. The expression of hydric adventitious roots can vary from only a few individual roots to a bushy abundance which may totally cover the stem. Hypertrophied lenticels are abnormally large lenticels which appear as expanded portions of the outer bark of stems and roots. These also appear to function as a mechanism to enhance opportunities for aerobic respiration. Look for hydric adventitious roots and hypertrophied lenticels on stems of flooded plants such as Myrica cerifera (wax myrtle), Ludwigia spp. (primrose willow) and Hypericum spp. (St. John's-wort). Expanded lenticels can also be found on many species of bottomland hardwood trees. Other examples of morphological plant adaptations produced in response to extended wetness are the conspicuous prop-roots of Rhizophora mangle (red mangrove), the "knees" of Taxodium distichum (bald cypress), and the buttressing of tree bases as exhibited by Nyssa sylvatica var. biflora (swamp tupelo), Ulmus americana (American elm) and Quercus laurifolia (swamp laurel oak). Caution: Once a morphological adaption develops it does not disappear if the site is drained and no longer functions as a wetland.

(10) Secondary flow channels are discrete and obvious natural pathways of water flow landward of the primary bank of a stream watercourse and typically parallel to the main channel. These often occur in conjunction with sediment deposition and water marks. Look for these along streams and rivers, especially adjacent to or within floodplain forests.

(11) Sediment deposition is mineral or organic matter deposited in or shifted to positions indicating water transport. The current of a river or stream during high flow carries sediment that is normally in equilibrium with the lower flow velocity and is thus retained near the bottom as bed flow. When a stream overflows its primary bank and occupies the floodplain, the resultant increase in capacity causes a sudden decrease in velocity in the water outside the main channel. This results in the over bank flow dropping its acquired sediment load in the floodplain usually but not always close to the primary bank. Look for material deposition on rocks and plants especially when the deposition is observed on the upstream surface and not on the downstream surface. Sediment deposited as erosion from uplands is not included in this indicator. 

(12) Vegetated tussocks or hummocks are areas where vegetation is elevated above the natural grade on a mound built up of plant debris, roots, and soils so that the growing vegetation is not subject to the prolonged

effects of soil anoxia. Look for these in hydric hammocks and in areas of shallow prolonged inundation or where the soil is saturated to the surface for long duration. Tree buttressing is often associated with tussocks or hummocks in saturated soils.

(13) Water marks. Water marks are created by the staining effect of a sustained water elevation. This will appear as a distinct line created on fixed objects, including vegetation. The length of time the object has been inundated influences the expression of this indicator, as does the color and sediment burden of the water. Look for this in conjunction with sediment deposition, especially along rivers and streams. Seasonal high

water marks in wetlands and other water bodies often appear related to the elevated lichen lines, aquatic moss and liverwort zones and water stained areas of trees, rocks and other objects.

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Last Modified:
February 26, 2018 - 10:17am

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