History of Wetland Soils
in the United States

Wetland Environments
Richard O. Sleezer

Table of Contents
Early approach Change in attitude
Soil taxonomy Hydric soil

Early approach

The Division of Agricultural Soils was created within the United States Department of Agriculture (USDA) in 1894 and soil survey work began in 1899 (Helms et al. 2002). One of the first summaries of soils and soil surveys in the United States was written by Milton Whitney who was the Chief of the Bureau of Soils within the USDA at that time (Whitney, 1909). Under Whitney, the Bureau of Soils divided the United States into 13 soil provinces and described the soils and soils series in each province. At that time soil surveys had only been completed for a relatively small portion of the coterminous United States. In the Atlantic and Gulf Coastal Plain Province, for example, wet soils were generally mapped in two categories (quoted from Whitney 1909, p. 116-117).

  1. Muck and Peat: These soils are composed largely of organic matter in various conditions of decay, the muck representing an advanced stage of change in peat areas. Of relatively limited extent and poorly drained, these soils are highly valued for their adaptation to special crops, such as celery, onions, peppermint and cabbage.

  2. Swamp, tidal swamp and marsh: Under these heads are grouped areas covered with water the greater part of the year and unfit for agriculture except where drained and protected from tidal or fluvial overflow. When reclaimed much of this land will become quite productive.

The bias of early soil science toward viewing soils only in terms of their agricultural potential can be clearly seen in the descriptions above. A particularly troubling and recurring term throughout the cited text above is the word reclaimed. Reclamation was, in the case of wet soils simply draining the water so that normal agricultural methods could be used to farm otherwise 'worthless' lands. In the River Flood Plains province, not only were the areas denoted 'Muck and Peat' and 'Swamp and Marsh' described as needing drainage but other map units as well. For example, “The Catalpa silt loam requires drainage, but when reclaimed is a very valuable general farming soil” (Whitney 1909, p. 125).

A comprehensive definition of the terms Marsh and Swamp can be found in a later publication of the Bureau of Soils which states that: In the soil classification of the Bureau of Soils the term “Swamp” is used to designate all areas which in their natural conditions are too wet for the production of any crop. Such areas are usually covered by standing water for much or all of the time. Swamps are covered with a variety of native vegetation, consisting chiefly of water-loving grasses, reeds, shrubs, and trees (Bonsteel 1912, p. 3). The word Marsh is used by contrast to designate low, wet, treeless areas, usually covered by standing water and supporting growth of coarse grass and rushes. The Marsh is subdivided into two classes. The first of these is the Tidal marsh, where broad stretches of low-lying and practically treeless land along the coast are subjected to inundation by the rising tide. The other class consists of the fresh-water areas in the uplands or near the heads of tidewater estuaries where fresh water is backed up over the marshland by each rising tide. (Bonsteel 1912, p. 3)

Bonsteel (1912) estimated that approximately 60 million acres of these “undrained lands” existed in the eastern United States alone. He also makes two telling statements in his summary (Bonsteel 1912, p. 12).

  1. The first necessity in the agricultural use of such areas consists in the drainage of the land.
  2. Extensive areas of Marsh and Swamp in the central prairie States have long been drained and utilized for agriculture. They constitute some of the most fertile and productive of the corn, oat, wheat, and grass soils of that section.

In these two statements and those above, he essentially crystallizes the prevailing view of wetlands by soil scientists, farmers, and others in the early 20th century. They were potential resources for agriculture because after drainage (reclamation), they would become excellent agricultural soils for most common crops. Management of wetlands for non-agricultural purposes was, therefore, nonexistent, and the accepted practice was to drain all such areas where ever economically feasible to put them into agriculture production.

Change in attitude

A change in attitude towards wetlands and wet soils began to emerge during the next 25 to 30 years. In 1938, the USDA Yearbook of Agriculture entitled “Soils and Men” was published and it contained chapters devoted to “Drainage in Arid Regions” (Thorp and Scofield 1938, p. 717-722) and to “Drainage in the Humid Regions” (Haswell 1938, p. 723-736), and there were some changes to the soil classification where the term Bog Soils was introduced above Peat and Muck in the classification hierarchy along with other categories or nomenclature to describe wet soils such as glei (gray because of reducing conditions) and planosols (strongly leached soils that are imperfectly or poorly drained) (Baldwin et al. 1938, p. 979-1001). It would appear the accepted practice of draining wet soils was continuing and the evolution of the classification of wet soils is interesting, but the most important chapter has more to do with an underlying current of policy change towards wet soils.

Kenney and McAtee (1938, p. 77-83) in a chapter entitled “The Problem: Drained Areas and Wildlife Habitats” pointed out that there were at least two important reasons why the indiscriminate draining of all wet soils may not be appropriate. The first issue they raised was economic in nature. They pointed out that drainage is an expensive proposition and that according to the 1930 census approximately 21,000,000 acres of land that had already been drained had not been settled largely because it was not suitable for agriculture even after drainage.

The second issue they raised was ecological in nature. They stated that, Drainage is beneficial to farming in so many ways that any possible disadvantages are often overlooked. While it has been an accepted and well-nigh universal farm practice, experience has taught that it is not everywhere and at all times wholly desirable. They go on to cite as examples of detrimental effects the large-scale drainage projects in the northern Great Plains that have severely reduced waterfowl populations and the detrimental effects of small-scale drainage on fur-bearing animals such as mink and muskrat elsewhere. The combination of these two issues (economics and ecology) were the starting points for major changes to the study and management of wet soils in the United States.

At the same time that changes in our views about how to best manage wet soils were changing, the classification system for soils was continuing to evolve. A system was needed that would classify soils based on what was observed in the field, with accompanying laboratory data where possible, without a climatic zone bias, and with sufficient detail and precision to be globally applicable. The decision was made in 1951 that a new soil system must be developed (Johnson 1975). What followed was a series of approximations of a new classification system, each of which received careful review nationally and internationally that eventually culminated in Soil Taxonomy (Soil Survey Staff 1975). The objective of soil taxonomy is to have hierarchies of classes that permit us to understand, as fully as existing knowledge permits, the relationships between soils and also between soils and the factors responsible for their character. (Soil Survey Staff 1975, p. 7).

Soil taxonomy

The nomenclature used in Soil Taxonomy is derived from mostly Greek and Latin words or parts of words that are added entirely or in part as formative elements at each successive classification level (Soil Survey Staff 1975; Buol et al. 1997). In its original form Soil Taxonomy contained 6 levels of classification which are in order from simplest to most complex: order, suborder, great group, subgroup, family, and series. A complete discussion is not possible here, but it is possible to go through the 1975 version of the classification with an eye toward the classification of wet soils and pick out the most important elements of Soil Taxonomy relevant to this discussion.

The ten original soil orders are listed in the following table along with formative elements and their meanings--see Table 1. Of these ten the only one that is clearly associated with wet soils would be the Histosols. The root element "histos" was used to indicate that these soils are composed largely of plant tissue (at least 20-30% in most of there upper parts, Soil Survey Staff 1975, p. 72). They are essentially the Peat, Bog, Half Bog, and Muck soils of earlier classifications. Obviously, the preservation of organic matter in these soils is associated with the predominance of saturated conditions (wetland soils though not as yet labeled as such).

Table 1. The original 10 soil orders and a description of their formative elements. Patterned after Soil Survey Staff (Johnson 1975, Table 8, p. 87).
Order Formative
Derivation of Elements Pronunciation
Meaningless Pedalfer
Latin--aridus, dry Arid
Meaningless Recent
Greek--histos, tissue Histology
Latin--inceptum, beginning Inception
Latin--mollis, soft Mollify
French--oxide Oxide
Greek--spodos, wood ash Odd
Latin--ultimus, last Ultimate
Latin--verto, turn Invert

Wet or at least seasonally wet classifications of soils were more common in the next level of classification, the suborder. The formative element "Aqu," from the Latin aqua meaning water, is added to soils that have so-called aquic moisture regimes. The aquic (L. aqua, water) moisture regime implies a reducing regime that is virtually free of dissolved oxygen because the soil is saturated by ground water or by water of the capillary fringe (Soil Survey Staff, 1975, pg. 54). These soils were generally identified in the field as soils whose dominant Munsell colors had chromas of 2 or less and also had brighter colored mottles (Soil Survey Staff 1975, p. 109).

In terms of taxonomic nomenclature then, a wet (aquic moisture regime) Alfisol would be referred to as belonging to the suborder Aqualf (Aqu for wet and alf for Alfisol). The same procedure was used for the other orders as appropriate forming six, "wet/aquic" suborders: Aqualfs (wet Alfisols), Aquents (wet Entisols), Aquepts (wet Inceptisols), Aquolls (wet Mollisols), Aquox (wet Oxisols), Aquods (wet Spodosols), and Aquults (wet Ultisols). The remaining formative elements for succeeding levels in Soil Taxonomy are added in a similar fashion to reach the series level of classification.

A final note, there is provision made for other modifiers in soil descriptions. One of those is the adjective "Hydric," from the Greek word hydor meaning water (Soil Survey Staff 1975, p. 87-90). The Hydric term is used for soils that do not have Aquic moisture regimes but do have excess water (wetness) at times during the year. As you will see the adjective Hydric has now taken on specific meaning for wet soils.

Hydric soil

Work by soil scientists to develop a practical and useful classification of wet soils started in the 1970s at the request of the U.S. Fish and Wildlife service to help with their National Wetlands Inventory (NWI) (Mausbach, 1994). The intent apparently was to create a hydric soil classification that correlated wet soils with hydrophytic vegetation. The definition of what a hydric soil is, how long they take to form, and how long in given years or under typical conditions they must be saturated to be called hydric soils has been refined considerably. Such issues are now under the purview of the National Technical Committee for Hydric Soils which was originally charged with finalizing a definition of hydric soils and creating a list of hydric soils in the early 1980s (Mausbach 1994) and continues to serve five major functions with regards to wet/hydric soils (paraphrased from the NTCHS website).

  1. Technical support.
  2. Updating and distribution of hydric soil lists.
  3. Refinement and maintenance of “Field Indicators of Hydric Soils.”
  4. Communication and public comments regarding hydric soil definition.
  5. Research investigations regarding data necessary to better define hydric soils.

The best and most up-to-date source for information about hydric soils and hydric soils definitions is the USDA/NRCS hydric soils web-site that includes definitions of terms, criteria, technical notes, lists of field indicators, and state and national lists of hydric soils. The current definition of a hydric soil is:

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. The concept of hydric soils includes soils developed under sufficiently wet conditions to support the growth and regeneration of hydrophytic vegetation. Soils that are sufficiently wet because of artificial measures are included in the concept of hydric soils. Also, soils in which the hydrology has been artificially modified are hydric if the soil, in an unaltered state, was hydric. Some series, designated as hydric, have phases that are not hydric depending on water table, flooding, and ponding characteristics.


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