than 30 feet deep. Organic soils also develop in 

 low-lying areas along coastal waters where tidal 

 flooding is frequent. 



3.11. Hydric organic soils are subdivided into 

 three groups based on the presence of identifiable 

 plant material: (1) muck (Saprists) in which two- 

 thirds or more of the material is decomposed and 

 less than one-third of the plant fibers are identifia- 

 ble; (2) peat (Fibrists) in which less than one-third 

 of the material is decomposed and more than two- 

 thirds of the plant fibers are still identifiable; and 

 (3) mucky peat or peaty muck (Hemists) in which 

 the ratio of decomposed to identifiable plant matter 

 is more nearly even (U.S.D.A. Soil Survey Staff 

 1975). A fourth group of organic soils (Folists) ex- 

 ists in tropical and boreal mountainous areas where 

 precipitation exceeds the evapotranspiration rate, 

 but these soils are never saturated for more than a 

 few days after heavy rains and thus do not develop 

 under hydric conditions. All organic soils, with the 

 exception of the Folists, are hydric soils. 



3.12. When less organic material accumulates in 

 soil, the soil is classified as mineral soil. Some 

 mineral soils may have thick organic surface layers 

 due to heavy seasonal rainfall or a high water table, 

 yet they are still composed largely of mineral matter 

 (Ponnamperuma 1972). Mineral soUs that are cov- 

 ered with moving (flooded) or standing (ponded) 

 water for significant periods or are saturated for ex- 

 tended periods during the growing season are clas- 

 sified as hydric mineral soils. Soil saturation may 

 result from low-lying topographic position, 

 groundwater seepage, or the presence of a slowly 

 permeable layer (e.g., clay, confining bedrock, or 

 hardpan). 



3.13. The duration and depth of soil saturation are 

 essential criteria for identifying hydric soils and 

 wetiands. Soil morphological features are com- 

 monly used to indicate long-term soil moisture re- 

 gimes (Bouma 1983). The two most widely recog- 

 nized features that reflect wetness in mineral soils 

 are gleying and mottiing. 



3.14. Simply described, gleyed soils are predomi- 

 nantiy neutral gray in color and occasionally green- 

 ish or bluish gray. In gleyed soils, the distinctive 

 colors result from a process known as gleization. 

 Prolonged saturation of mineral soil convens iron 

 from its oxidized (ferric) form to its reduced (ferro- 

 us) state. These reduced compounds may be com- 

 pletely removed from the soil, resulting in gleying 



(Veneman, et al. 1976). Mineral soils that are al- 

 ways saturated are uniformly gleyed throughout the 

 saturated area. Soils gleyed to the surface layer are 

 hydric soils. These soils often show evidence of 

 oxidizing conditions only along root channels. 

 Some nonhydric soils have gray layers (E- 

 horizons) immediately below the surface layer that 

 are gray for reasons other than saturation (e.g., 

 leaching due to organic acids). These soils often 

 have brighter (e.g., brownish or reddish) layers 

 below the gray layer and can be recognized as non- 

 hydric on that basis. 



3 15. Mineral soils that are alternately saturated 

 and oxidized (aerated) during the year are usually 

 mottied in the part of the soil that is seasonally wet. 

 Motties are spots or blotches of different colors or 

 shades of colors interspersed with the dominant 

 (matrix) color. The abundance, size, and color ot 

 the mottles usually reflect the duration of the satu- 

 ration period and indicate whether or not the soil is 

 hydric. Mineral soils that are predominantly gray- 

 ish with brown or yellow mottles are usually satu- 

 rated for long periods during the growing season 

 and are classified as hydric. Soils that are predomi- 

 nantiy brown or yellow with gray motties are satu- 

 rated for shorter periods and may not be hydnc. 

 Mineral soils that are never saturated are usually 

 bright-colored and are not mottied. Realize, how- 

 ever, tiiat in some hydric soils, mottles may not be 

 visible due to masking by organic matter (Parker, 

 etal 1984). 



3.16. It is important to note tiiat the gleization and 

 mottie formation processes are strongly influenced 

 by the activity of certain soil microorganisms. 

 These microorganisms reduce iron when the soil 

 environment is anaerobic, that is, when virtually no 

 free oxygen is present, and when the soil contains 

 organic matter. If the soil conditions are such that 

 free oxygen is present, organic matter is absent, or 

 temperatures are too low (below 41°F) to sustain 

 microbial activity, gleization will not proceed and 

 mottles will not form, even though the soil may be 

 saturated for prolonged periods of time (Diers and 

 Anderson 1984). 



Soil Colors 



3 17 Soil colors often reveal much about a soil's 

 wetness, that is, whether the soil is hydric or non- 

 hydric Scientists and others examining the soil can 

 detennine the approximate soil color by companng 



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