Wetlands are an important component of our diverse ecosystem because they store flood water, improve water quality, and provide habitat to wildlife. Current federal regulations require that a permit from the U.S. Army Corps of Engineers or the Natural Resources Conservation Service be obtained before a user can disturb an existing wetland. Therefore, identifying wetland boundaries has received national attention and has become somewhat controversial.
Wetlands are defined on the basis of three parameters: hydrology, hydrophytic vegetation, and hydric soils. Since imposition of the current federal legislation, delineating exact wetland boundaries as accurately, inexpensively, and quickly as possible has become essential to both landowners and wetland regulators. Wetland boundaries usually coincide with the point where hydric soils end and upland soils begin.
Hydric soil identification is normally done by looking for indicators that show the soils have been chemically reduced. Such indicators include redoximorphic features, or, as formerly called, gray and red mottles. When these colors occur near the soil surface, hydric soils are easily identified. Not all hydric soils develop redoximorphic features. These are the Problem Soils for which wetland delineation is difficult.
This publication, based on a symposium held at the annual meeting of the Soil Science Society of America in Seattle, WA, focuses on the problem of identifying hydric soils when redoximorphic features are not present. The contributors to this treatise have a wealth of research and practical experience related to this topic.
This publication underscores the importance that soil science plays in solving environmental problems. Although soil scientists are relatively few in number, they can and must play an essential role in resolving complex environmental issues such as wetland delineation.
D. K. Cassel
Identification of soil horizons that are saturated and reduced is relatively easy using soil morphology for most soils. For some soils, however, the morphology does not show the normal indicators of wetness and reduction. The purpose of this special publication is to collect and analyze the most recent data for soils in which identification of saturated and reduced conditions is difficult. These soils frequently do not possess, and in some cases do not develop, the traditional indicators of saturation and reduction such as low chroma or gray colors with associated bright red mottles. These indicators are now called redoximorphic features.
With the exception of Chapter 1, each chapter is devoted to a different problem soil. Reasons for the lack of redoximorphic features in these soils are not well understood, but the prevailing theories will be summarized here.
For example, sandy soils such as Psammaquents and some Aquods usually have too little Fe to form redoximorphic features, and the materials are frequently gray in color in most horizons below the A horizon. Mollisols are problem soils because the thick, black, mollic epipedon apparently contains organic materials that mask redox concentrations or depletions.
Vertisols are problem soils because their shrinking and swelling may disrupt redoximorphic features and mix them into the matrix. The black color of many Vertisols also presents the same problems found in Mollisols.
Aridisols and related saline soils don't develop redoximorphic features, possibly because they are rarely saturated or when saturated they are not reduced. It also has been hypothesized that the pH of Aridisols is too high and organic matter contents too low for Fe reduction to occur. These soils frequently occur in desolate areas such that data on wetness are not available. Usually there are no eyewitnesses to even attest to past wetness events.
Andisols or soils of volcanic deposits may not develop redoximorphic features because the glassy nature of their particles may seal the Fe inside the particles. Thus, while the soils contain Fe, very little of it is susceptible to reduction. Soils in Alaska have generally been assumed to be too cold for reducing chemical reactions to occur.
Lastly, many Entisols or young soils also do not contain redoximorphic features, even ones in areas that have obviously been flooded. It has generally been assumed that this is because the features require long periods to form. Sufficient time apparently has not passed to enable redoximorphic features to develop to the point that they are visible.
These are just some of the theories that will be examined in the following chapters. The authors have assembled the most up-to-date information available on these problem soils. Much of the data was generated through the USDA-NRCS's “Wet Soils Monitoring Project” which was initiated and headed by Warren Lynn. We thank Dr. Lynn for not only making the data available, but for also doing data searches needed by the authors of several chapters.
Not all questions regarding these soils will be answered; however, the areas where questions remain point to where more research is needed.
M. J. Vepraskas
North Carolina State University
S. W. Sprecher
U. S. Army Corps of Engineers
J. C. Bell Associate Professor, Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108-6028
Janis L. Boettinger Assistant Professor, Department of Plants, Soils, and Biometeorology, Utah State University, Logan, UT 84322-4820
R.B. Brown Professor and Chair, Soil and Water Science Department, University of Florida, Gainesville, FL 32611
Mark H. Clark Soil Scientist, Natural Resources Conservation Service, 268 E. Fireweed, Palmer, AK 99645
N.B. Comerford Professor, Soil and Water Science Department, University of Florida, Gainesville, FL 32611
R.W. Griffin Professor, Cooperative Agricultural Research Center, Prairie View A&M University, Prairie View, TX 77446-4079
J.H. Huddleston Professor, Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331-7306
J.S. Jacob Research Fellow, Environmental Institute of Houston, University of Houston-Clear Lake, Houston, TX 77058-1098
R.J. Kuehl Research Assistant, Soil and Water Science Department, University of Florida, Gainesville, FL 32611
David L. Lindbo Assistant Professor, Department of Soil Science, Vernon James Center, North Carolina State University, 207 Research Station Rd., Plymouth, NC 27962
P.A. McDaniel Associate Professor, Department of Plant, Soils, and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339
S.L. McGeehan Research and Instructional Associate, Department of Plants, Soils, and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339
W.L. Miller Soil Scientist, Natural Resources Conservation Service, 312 S. Main St., Federal Building, Room 310, Victoria, TX 77901
Chien-Lu Ping Professor, Agriculture and Forestry Experiment Station, University of Alaska-Fairbanks, Palmer, AK 99645
J.L. Richardson Professor, Department of Soil Science, North Dakota State University, Fargo, ND 58105-5638
S.W. Sprecher Soil Scientist, Environmental Laboratory, U. S. Army Corps of Engineers, Waterways Experiment Station, 3909 Halls Ferry Rd., Vicksburg, MS 39180-6199
M.J. Vepraskas Professor, Department of Soil Science, Box 7619, North Carolina State University, Raleigh, NC 27695-7619
L.P. Wilding Professor, Department of Soil & Crop Sciences, Texas A&M University, College Station, TX 77843