40454 Federal Register / Vol. 56, No. 157 / Wednesday, August 14, 1991 / Proposed Rules 



most obvious and revealing hydrologic 

 indicator may be simply observing the 

 areal extent of inundation. However, 

 both seasonal conditions and recent 

 weather conditions must be considered 

 when observing an area because they 

 can affect the presence of surface water 

 on wetland and nonwetland sites. In 

 many cases, soils saturated at the 

 surface are obvious, since the ground 

 surface is soggy or mucky under-foot. 



To observe free water at the surface it 

 may be necessary to dig a hole and 

 observe the level at which water stands 

 in the hole after sufficient time has been 

 allowed for water to drain into the hole. 

 In some cases, the upper level at which 

 water is flowing into the hole can be 

 observed by examining the walls of the 

 hole. This level may represent the depth 

 to the water table. In some heavy clay 

 soils, however, water may not rapidly 

 accumulate in the hole even when the 

 soU is saturated. When attempting to 

 observe the level of free water in a bore 

 hole, adequate time should be allowed 

 for water in the hole to reach 

 equilibrium with the water table. 



Soil saturation at the surface may be 

 detected by a "squeeze test" or "shake 

 test" which involve taking a surface soil 

 sample and squeezing or shaking the 

 sample. If water can be extracted, the 

 soil is considered saturated at the 

 surface. 



When evaluating soil saturation, both 

 the season of the year and the preceding 

 weather conditions must be considered, 

 since excess water may not be present 

 during parts of the growing season in 

 some wetlands due to high evaporation 

 and plant transpiration rates which 

 effectively lower the water table. At 

 such times, other indicators of wetland 

 hydrology may be present. 



Other Signs of Wetland Hydrology 



It is not necessary to observe 

 inundation or saturation at the time of 

 freld inspection to identify wetland 

 hydrology so long as Indicators are 

 sufflcient to demonstrate to field 

 personnel that Uie weUand hydrology 

 criterion is met Other signs of wetland 

 hydrology may be observed, e.g., 

 oxidized rhizospheres (root channels). 



Some plants are able to survive 

 saturated soil conditions (i.e., a reducing 

 environment) because they can 

 transport oxygen to their root zone. Iron 

 oxide concretions (orangish or reddish 

 brown in color) may form along the 

 channels of living roots and rhizomes 

 creating oxidized rhizospheres that 

 provide evidence of soil saturation 

 (anaerobic conditions) for a significant 

 period during the growing season. 

 Ephemeral or temporary oxidized 

 rhizospheres may develop after 



abnormally heavy rainfall periods. 

 Consequentiy, oxidized rhizospheres are 

 most meaningful when observed with 

 other weUand indicators especially in 

 undrained soils displaying diagnostic 

 hydric soil properties. 



Other signs that may reflect weUand 

 hydrology include water marks, drift 

 lines, water-borne deposits, surface- 

 scoured areas, weUand drainage 

 patterns, and certain plant 

 morphological adaptations. 



(1) Water marks are found most 

 commonly on woody vegetation or fixed 

 objects (e.g., bridge pillars, buildings, 

 and fences) but may also be observed 

 on other vegetation. They often occur as 

 dark stains on bark or other fixed 

 objects. 



(2) Drift lines are typically found 

 adjacent to streams or others sources of 

 water flow in weUands and often occur 

 in tidal marshes. Evidence consists of 

 deposition of debris in a line on the 

 weUand surface or debris entangled in 

 aboveground vegetation or other fixed 

 objects. Debris usually consists of 

 remnants of vegetation (branches, 

 stems, and leaves), litter, and other 

 water-borne materials often deposited 

 more or less partUlel 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 that 

 indicated by a drift line. The drift lines 

 in tidal wetlands are often referred to as 

 "wrack lines." 



(3) Water-bome deposits of mineral 

 or organic matter may be observed on 

 plants and other objects after 

 inundation. This evidence may remain 

 for a considerable period before it is 

 removed by precipitation or subsequent 

 inundation. Silt deposition in vegetation 

 and other objects provides an indication 

 of the minimum inundation level. When 

 the deposits are primarily organic (e.g., 

 fine organic material and algae), the 

 detritus may become encrusted on or 

 slighUy above the soil surface after 

 dewatering occurs. Sediment deposits 

 (e.g., sandy material) along streams 

 provide evidence of recent overbank 

 flooding. 



(4) Surface scouring occurs along 

 floodplains where overbank flooding 

 erodes sediments (e.g., at the bases of 

 ti-ees). The absence of leaf litter from the 

 soU surface is also sometimes an 

 indication of surface scouring. Forested 

 weUands that contain standing waters 

 for relatively long duration will 

 occasionally have areas of bare or 

 essentially bare soil, sometimes 

 associated v«th local depressions. 



(5) Many plants growing in weUands 

 have developed morphological features 



in response to inundation or soil 

 saturation. Examples include 

 pneumatophores (e.g., cypress knees), 

 prop roots, floating stems and leaves, 

 hypertrophied lenticels (oversized stem 

 pore), aerenchyma (air-filled)"tissue in 

 roots and stems, buttressed tree trunks, 

 multiple trunks, adventitious roots, 

 shallow root systems, polymorphic 

 leaves, inflation leaves, stems or roots. 

 Pneumatophores, prop roots, floating 

 stems and leaves, hypertrophied 

 lenticels, aerenchyma tissue, and 

 buttressed tree trunks develop virtually 

 only in weUand or aquatic environments 

 and therefore are listed as primary 

 hydrologic indicators in the wetland 

 hydrology criterion. When these 

 features are observed in young plants, 

 they provide good evidence that 

 wetland hydrology exists. Multiple 

 trunks, adventitious roots, shaUow root 

 systems, polymorphic leaves, inflated 

 leaves, stems or roots are commonly 

 found in many weUand plants, yet not 

 exclusive to them, and therefore are 

 Usted as secondary hydrologic 

 indicators in the wetland hydrology 

 criterion and indicate weUands only 

 when accompanied by other collateral 

 information that indicates weUand 

 hydrology. 



Hydrophytic Vegetation Criterion 



An area meets the hydrophytic 

 vegetation criterion if, under normal 

 circumstances, a frequency analysis of 

 all species vdthin the conununity yields 

 a prevalence index value of less than 3.0 

 (where OBL = 1.0, FACW = 2.0, FAC = 

 3.0, FACU = 4.0, and UPL = 5.0). 



Note: Specific wetland types that may have 

 vegetation that does not meet this criterion 

 are listed as exceptions. Areas where the 

 vegetation has been removed will generally 

 meet the hydrophytic vegetation criteria if 

 they are capable of supporting such 

 vegetation. (See disturbed areas section) 



Hydrophytic Vegetation Background 



The term "hydrophytic vegetation" 

 describes plants that live in conditions 

 of excess wetness. For purposes of this 

 manual, hydrophytes are defiined as 

 macrophytic plant life growing in water 

 or on submerged substrates, or in soil or 

 on a substrate that is at least 

 periodically anaerobic (deficient in 

 oxygen) as a result of excessive water 

 content All plants growing in weUands 

 have adapted in one way or another to 

 life in permanenUy or periodically 

 inundated or saturated soils. Some 

 plants have developed structural or 

 morphological adaptations to inundation 

 or saturation, while others have broad 

 ecological tolerances (Tiner, 1991). Some 

 of these adaptive features are used as 



