Most soils are aerobic. This is important because plant roots respire (that is, they consume oxygen and carbohydrates while releasing carbon dioxide) and there must be sufficient air—especially oxygen—in the soil to support most forms of soil life. Air normally moves through interconnected pores by forces such as changes in atmospheric pressure, the flushing action of rainwater, and by simple diffusion.
In addition to plant roots, most forms of soil microorganisms need oxygen to survive. This is true of the more well-known soil animals as well, such as ants, earthworms and moles. But soils can often become saturated with water due to rainfall and flooding. Gas diffusion in soil slows (some 10,000 times slower) when soil becomes saturated with water because there are no open passageways for air to travel. When oxygen levels become limited, intense competition arises between soil life forms for the remaining oxygen. When this anaerobic environment continues for long periods during the growing season, quite different biological and chemical reactions begin to dominate, compared with aerobic soils. In soils where saturation with water is prolonged and is repeated for many years, unique soil properties usually develop that can be recognized in the field. Soils with these unique properties are called hydric soils, and although they may occupy a relatively small portion of the landscape, they maintain important soil functions in the environment.[1]
The plants found in hydric soils often have aerenchyma, internal spaces in stems and rhizomes, that allow atmospheric oxygen to be transported to the rooting zone.[2] Hence, many wetlands are dominated by plants with aerenchyma;[3] common examples include cattails, sedges and water-lilies.
Technical definitionsedit
United Statesedit
A hydric soil is defined by federal law[4] to mean "soil that, in its undrained condition, is saturated, flooded, or ponded long enough during a growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation". This term is part of the legal definition of a wetland included in the United StatesFood Security Act of 1985 (P.L. 99-198). This definition is provided in the controlling regulations to the Wetland Conservation Provisions of the FSA of 1985(7 C.F.R 12) and is used by the U.S.D.A. Natural Resources Conservation Service in the administration of the Wetland Conservation Compliance provisions ("Swampbuster") contained in the FSA of 1985. In adopting this definition in 1985, Congress attempted to capture the duration of waterlogged condition of a hydric soil by adding that a hydric soil is waterlogged long enough to support not only the growth of plants adapted to life in anaerobic conditions but also the regeneration of such plants.
Another common definition of a hydric soils is provided by the National Technical Committee of Hydric Soils (NTCHS) as "a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part."[5] The NTCHS hydric soil definition is used by the U.S. Army Corps of Engineers and the Environmental Protection Agency in their joint responsibilities in the administration of Section 404 of the Clean Water Act (1972).
^Schuyt, K. and Brander, L. 2004. Living Waters: Conserving the Source of Life – The Economic Values of theWorld’sWetlands. Amsterdam, the Netherlands: European Union, and Gland, Switzerland: World Wildlife Fund.
^Justin, S. H. F. W. and Armstrong, W. 1987. The anatomical characteristics of roots and plant response to soil flooding. New Phytologist 106: 465–95.
^Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK.
^Food Security Act(FSA) of 1985 16 U.S.C. Section 3801(a)(2)
^This definition (Federal Register, July 13, 1994) replaced the older 1991 version and accomplished two things. First, a soil that is artificially drained or protected (ditches, levees, etc.) is a hydric soil if the soil in its undisturbed state meets the definition of a hydric soil. Estimated soil properties for manipulated soils are based on best professional estimates of the properties thought to exist before manipulation. Second, the link between the definition and criteria was removed.
Bibliographyedit
Environmental Laboratory. 1987. Corps of Engineers Wetland Delineation Manual, Technical Report Y-87-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss. Url () last accessed 2006-04-16
Soil Conservation Service. 1994. National Food Security Act Manual. Title 180. USDA Soil Conservation Service, Washington, D.C.
Soil Survey Staff. 1999. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. USDA Natural Resources Conservation Service, Agric. Hdbk. 436, U.S. Government Printing Office, Washington, D.C. 869 pp.
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Hydric soil is soil which is permanently or seasonally saturated by water resulting in anaerobic conditions as found in wetlands Contents 1 Overview 2 Technical definitions 2 1 United States 3 See also 4 References 5 Bibliography 6 External linksOverview editMost soils are aerobic This is important because plant roots respire that is they consume oxygen and carbohydrates while releasing carbon dioxide and there must be sufficient air especially oxygen in the soil to support most forms of soil life Air normally moves through interconnected pores by forces such as changes in atmospheric pressure the flushing action of rainwater and by simple diffusion In addition to plant roots most forms of soil microorganisms need oxygen to survive This is true of the more well known soil animals as well such as ants earthworms and moles But soils can often become saturated with water due to rainfall and flooding Gas diffusion in soil slows some 10 000 times slower when soil becomes saturated with water because there are no open passageways for air to travel When oxygen levels become limited intense competition arises between soil life forms for the remaining oxygen When this anaerobic environment continues for long periods during the growing season quite different biological and chemical reactions begin to dominate compared with aerobic soils In soils where saturation with water is prolonged and is repeated for many years unique soil properties usually develop that can be recognized in the field Soils with these unique properties are called hydric soils and although they may occupy a relatively small portion of the landscape they maintain important soil functions in the environment 1 The plants found in hydric soils often have aerenchyma internal spaces in stems and rhizomes that allow atmospheric oxygen to be transported to the rooting zone 2 Hence many wetlands are dominated by plants with aerenchyma 3 common examples include cattails sedges and water lilies Technical definitions editUnited States edit A hydric soil is defined by federal law 4 to mean soil that in its undrained condition is saturated flooded or ponded long enough during a growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation This term is part of the legal definition of a wetland included in the United States Food Security Act of 1985 P L 99 198 This definition is provided in the controlling regulations to the Wetland Conservation Provisions of the FSA of 1985 7 C F R 12 and is used by the U S D A Natural Resources Conservation Service in the administration of the Wetland Conservation Compliance provisions Swampbuster contained in the FSA of 1985 In adopting this definition in 1985 Congress attempted to capture the duration of waterlogged condition of a hydric soil by adding that a hydric soil is waterlogged long enough to support not only the growth of plants adapted to life in anaerobic conditions but also the regeneration of such plants Another common definition of a hydric soils is provided by the National Technical Committee of Hydric Soils NTCHS as a soil that formed under conditions of saturation flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part 5 The NTCHS hydric soil definition is used by the U S Army Corps of Engineers and the Environmental Protection Agency in their joint responsibilities in the administration of Section 404 of the Clean Water Act 1972 See also edit nbsp Wetlands portal Acid sulfate soil Blue goo Gley soil Mesic Redox Wade Hurt XericReferences edit Schuyt K and Brander L 2004 Living Waters Conserving the Source of Life The Economic Values of theWorld sWetlands Amsterdam the Netherlands European Union and Gland Switzerland World Wildlife Fund Justin S H F W and Armstrong W 1987 The anatomical characteristics of roots and plant response to soil flooding New Phytologist 106 465 95 Keddy P A 2010 Wetland Ecology Principles and Conservation 2nd edition Cambridge University Press Cambridge UK Food Security Act FSA of 1985 16 U S C Section 3801 a 2 This definition Federal Register July 13 1994 replaced the older 1991 version and accomplished two things First a soil that is artificially drained or protected ditches levees etc is a hydric soil if the soil in its undisturbed state meets the definition of a hydric soil Estimated soil properties for manipulated soils are based on best professional estimates of the properties thought to exist before manipulation Second the link between the definition and criteria was removed Bibliography editEnvironmental Laboratory 1987 Corps of Engineers Wetland Delineation Manual Technical Report Y 87 1 U S Army Engineer Waterways Experiment Station Vicksburg Miss Url pdf last accessed 2006 04 16 Soil Conservation Service 1994 National Food Security Act Manual Title 180 USDA Soil Conservation Service Washington D C Soil Survey Staff 1999 Soil Taxonomy A Basic System of Soil Classification for Making and Interpreting Soil Surveys USDA Natural Resources Conservation Service Agric Hdbk 436 U S Government Printing Office Washington D C 869 pp Soil Survey Staff 1994 National Soil Survey Handbook USDA Soil Conservation Service Washington D C External links editHydric Soils Technical Note 1 Proper use of Hydric Soil Terminology USDA NRCS Accessed 2006 04 16 Retrieved from https en wikipedia org w index php title Hydric soil amp oldid 1181407166, wikipedia, wiki, book, books, library,
