For information on wetlands see:
The water table marks the top of the saturated zone. Most agronomic plants, since they need oxygen for root growth, depend on the unsaturated zone for water. The saturated zone stores water that can be used for irrigation, human use, and the filling of wetlands.
When the saturated zone is near the surface of the earth, a wetland is
formed. "Wetland" is the collective term for marshes, swamps, bogs,
and similar areas that often develop between open water and dry land. In the
past, wetlands were often regarded as wastelands that contained mosquitoes,
flies, and unpleasant odors.
In the upper Midwest, many of the natural wetlands, when drained, made excellent agricultural soils. Because of this, more than half of America's wetlands have been converted to farmland, filled for housing developments or industry, or used as receptacles for household and hazardous waste.
Wetlands are mostly semi-aquatic lands that are either inundated or saturated by water for varying periods of time during the growing season. The growth of specially adapted plants (hydrophytes) is favored. The soils develop characteristic hydric properties.
Federal regulations implementing Section 404 of the Clean Water Act define
wetlands as
" those areas that are inundated or saturated by surface or groundwater
at a frequency and duration sufficient to support, and that under normal
circumstances do support, a prevalence of vegetation typically adapted for life
in saturated soil conditions."
A wide variety of wetlands have formed across the country due to regional and local differences in vegetation, hydrology, water chemistry, soil variation, topography, and climate. A definition of "hydric soils" was developed in 1991 by the US Department of Agriculture, Natural Resource Conservation Service to assist in determining which land areas should be classified as wetlands.
Thus: 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
Mottled soil (soil with two colors of red and gray) indicates zones of soil
wetness. Mottles and gray soil colors are signs of redoximorphic
features which indicate wetness.
Soil colors with Chromas < 2 indicate hydric soils.
Criteria for wetlands use the basic soil properties of water table depth,
flooding, and ponding; the soil quality and permeability; and classes of soil
taxonomy (Aquic) and natural soil drainage classes of very poorly, poorly and
somewhat poorly drained classes .
Hydric Soil 1 and Hydric Soil 2
In their natural condition, wetlands provide many benefits including food
and habitat for fish and wildlife, water quality improvement, flood protection,
shoreline erosion control, and opportunities for recreation and aesthetic
appreciation. Wetlands can also be used to treat sewage from small to large
developments when a city sewer is not available . To learn more about this go
to Constructed Wetlands
Each wetland works in combination with other wetlands as part of a complex, integrated system that delivers these benefits and others to society. An assessment of the value of any specific wetland must take this interrelationship into account.
Determining the value of a wetland is very difficult because of the hard-to-measure social values that it creates. A 5.2 ha/13 acre wetland south of Eagan, Minnesota was purchased by the federal government for $525,000 in 1992. The wetland included a calcareous fen, a rare type of wetland. This area will become part of the Minnesota Valley National Wildlife Refuge. The land was purchased from a developer who intended to develop the property, but had difficulty in obtaining federal permits.
Wetlands help maintain and improve the water quality of our nations' rivers
and other water bodies. Wetlands do this by removing and retaining nutrients,
processing chemical and organic wastes, and reducing sediment loads to
receiving waters. Wetlands are particularly good water filters. Due to their
position between upland and deep water, wetlands can intercept surface-water
runoff from land before it reaches open water. 
Wetlands also filter nutrients that have been removed from upland areas due to water erosion or ground water flow. This is especially important for nitrogen and phosphorus. As wetlands have been removed, more of these nutrients moved into lakes and rivers, causing excess vegetative and algae growth which results in cultural eutrophication of water bodies.
Cultural eutrophication describes human-generated fertilization of water
bodies. The main sources of phosphates and nitrates for this process are
treated sewage and runoff from farms and urban areas. Nitrates and phosphates
are the most common limiting factors for organism growth, especially in aquatic
ecosystems. Nitrates are supplied in limited quantities by decaying plant
material and nitrogen-fixing bacteria, but phosphates must come from bones,
organic matter or phosphate rocks. Consequently, the use of phosphate
detergents, combined with agricultural or urban runoff, has greatly affected
many water bodies by increasing the nutrients available for algae and weed
growth.
.
As water moves through a wetland it leaves behind nutrients that are used by the plants and animals living in the wetland. Wetlands have often been referred to as natural sponges that absorb flooding waters. They actually function more like natural tubs, storing either flood waters that overflow riverbanks or surface waters that collect in isolated depressions. By doing so, wetlands help protect down-stream property from flooding. Wetland vegetation helps to slow the speed of the flood waters, keeping more water out of the rivers. Since urban development increases the rate and volume of surface-water runoff, wetlands within and upstream from urban areas are especially valuable for flood protection.
Wetlands are being lost at an alarming rate. About 40 million ha/100 million
acres have been lost since 1600, but 11 million of these were lost between 1950
and 1970, only 20 years. The average annual loss was 185,000 ha /458,000 acres
with agricultural drainage responsible for 87% of the losses. With these
losses, we no longer have the benefits they once provided.
Section 404 of the Clean water act establishes the major federal program that regulates activities in wetlands. Under this law, the discharge of dredged or fill material into waters of the United States (including most wetlands) requires a permit from the Army Corps of Engineers. Failure to obtain a permit or to comply with terms of a permit can result in civil and/or criminal penalties.
The law sets certain environmental criteria for permitting projects in wetlands as well as the procedures for determining whether the project is in the public interest.
States have also enacted wetland protection laws, however fewer than 20 states have laws to protect inland wetlands. Where they exist, such laws often regulate only specific activities or apply only to certain wetland types or size. In Minnesota professionals in wetland science can obtain a certificate in this field. For information on the Wetland Delineator Certification Program go to http://www.mnwetlands.umn.edu/cert/
The movement to conservation of wetlands has encouraged the
"reconstruction" of wetlands that have been destroyed through a no
net loss policy. Restored wetlands have resulted in accruing the same benefits
that the original wetlands imparted to the environment.
Wetlands are an important part of our national heritage. They provide a
vital link between our land and water resources. As wetlands are lost the
remaining wetlands become even more valuable. The extensive wetlands of
northern Minnesota are valuable natural resource.
View
of the patterned peatland from the bog. Patterened
Peatland
References: U.S.A. Environmental Protection Agency. 1988.
America's Wetlands: Our vital link between and and water. OPA-87-016, U.S.A..
Govt.. Print. Office, Washington. D.C.
Kohnke, Helmut and D.P. Franzmier, 1995. Soil Science Simplified, 4th ed.
Wavelands, Prospect Heights, Ill.
Mausbach, M.J. 1994. Classification of Wetland Soils for Wetland
Identification. Soil Survey Horizons,35:1 pp 17:25.
Moore, J.E, A Zaporozec, & J.W. Mercer. 1995. Groundwater - A Primer.
American-Geological Institute. Alexandria VA.
Used to describe soil moisture conditions on an annual basis. They are: aquic, aridic, udic, and ustic. Click on the moisture regime to see a soil from a state that is an example of the specific moisture regime.
aquic-A mostly reducing soil moisture regime nearly free of dissolved oxygen due to saturation by groundwater or its capillary fringe and occurring at periods when the soil temperature at 50 cm below the surface is >5 º C.
Picture of Aquic Soil
aridic-A soil moisture regime that has no water available for plants for more than half the cumulative time that the soil temperature at 50 cm below the surface is > 5º. C, and has no period as long as 90 consecutive days when there is water for plants while the soil temperature at 50 cm is continuously > 8 º C.
Picture of Aridic Soil
udic-A soil moisture regime that is neither dry for as long as 90 cumulative days nor for as long as 60 consecutive days in the 90 days following the summer solstice at periods when the soil temperature at 50 cm below the surface is above 5º C.
Picture of Udic Soil
ustic-A soil moisture regime that is intermediate between the aridic and udic regimes and common in temperate subhumid or semiarid regions, or in tropical and subtropical regions with a monsoon climate. A limited amount of water is available for plants but occurs at times when the soil temperature is optimum for plant growth.
Picture of Ustic Soil
xeric-A soil moisture regime common to Mediterranean climates that have moist cool winters and warm dry summers. A limited amount of water is present but does not occur at optimum periods for plant growth. Irrigation or summer fallow is commonly necessary for crop production.
Xeric Soil
Soil Moisture Regime Map of the World 
Perudic: A udic soil moisture regime in which water moves through the soil in all months when it is not frozen. (A suborder in the U.S. system of soil taxonomy.)
Gelisols can occur in both the Permafrost and Interfrost regions. Gelisols
Frozen Soils=Study of Frozen Soils
Interfrost=seasonally and intermittently frozen groundInterfrost
Soil Site
Soil Water Chapters
© Regents of the University of Minnesota, 2007 The University of Minnesota is an equal opportunity educator and employer.
