Wetlands are an important component of many landscapes and have become a critical issue for both federal and state policymakers as the public desires to protect the ecological, biological and hydrological contributions of these important natural environments. A major issue facing local, state and Federal agencies is the development of criteria for identifying and delineating wetlands as they are found in a landscape. Although numerous definitions of wetlands have been proposed, they all contain three common characteristics: hydrology, soil, and vegetation.
Soil processes are influenced by and interact with the hydrologic cycle. The hydrologic cycle controls a variety of soil processes, the end-products of which may be reflected in morphologic properties of soils. Many of these morphologic features, such as soil color, are useful criteria for the field identification of wetlands. In addition, hydrology strongly influences the aeration status of soils which in turn affects the observable oxidation-reduction status of iron and manganese. The complex interactions of hydrology, soil, and vegetation emphasize the need for ongoing studies to elucidate the basic chemical, physical, and biological properties in soils.
The Soil Science Society of America Special Publication Quantifying Soil Hydromorphology is a compilation of 14 papers presented at a symposium held at the 1996 annual meeting of the Soil Science Society of America. The majority of the chapters describe original research findings of prominent soil scientists. The Soil Science Society of America is committed to communicating the results of critical research studies so the discipline of soil science can contribute to a better understanding of our wetland environments.
LEE E. SOMMERS, president Soil Science Society of America
The chapters in this Soil Science Society of America Special Publication are the result of papers contributed to a symposium of the same title, sponsored by Divisions S-5 and S-10 and Committee S-884 of the Soil Science Society of America at the 1996 meetings in Indianapolis, Indiana. The goal of this symposium was to bring together the most current research information relating soil morphological features to quantifiable hydrological or biogeochemical parameters associated with soil wetness. At this time public interest in wetlands and hydric soils is growing and the publication of Field Indicators of Hydric Soils in the United States (USDA-NRCS, 1998) has underlined the importance of using soil morphological properties in interpreting soil hydrology. The purpose of this SSSA Special Publication is to provide a focused forum for the dissemination of current hydropedological research. Because a significant number of scientists are conducting research on soil hydromorphology, essentially all of the chapters in this publication represent original research. Only the keynote paper by Veneman et al. (Chapter 1) is a review of previous research.
The articles in this publication critically discuss the quantification of soil hydromorphology by comparing observed soil hydrology with macro- and micro-morphological features found in the soil profile. The studies cover a broad spectrum of geomorphic and climatic conditions across the continental USA including the Atlantic Coastal Plain in Maryland, Virginia and Georgia, glacial sediments in Pennsylvania, levees along the Mississippi River, the Southern Plains of Texas, Vernal Pools in California, and the Willamette Valley in Oregon. Veneman et al. (Chapter 1) provide a historical perspective on past hydropedological research. Much of the early work was largely qualitative, followed by efforts to quantify environmental observations with soil morphological features leading to current efforts to understand pedogenic processes in the genesis of seasonally wet soils.
Quantification of soil biophysical processes and their association with soil hydromorphic features is the prime focus of most of the studies. Stolt et al. (Chapter 2) describe a reduction in iron and manganese levels and development of hydromorphic features within constructed soil peds exposed to saturated and reducing conditions over a 2-year period providing that a source of organic matter is present. In the Upper Coastal Plain of Virginia, Genthner et al. (Chapter 3) discuss seasonally high water tables occurring above redoximorphic features for well- and moderately well-drained soils and the opposite case for poorly and very poorly drained soils.
Szögi and Hudnall (Chapter 4) describe a good correlation between water table depth probabilities and the occurrence of reducing conditions, however, the relation of water tables with hydromorphic features does not appear so straightforward. Galusky et al. (Chapter 5) propose a methodology to estimate long-term trends in water table behavior using short-term soil hydrologic monitoring data and long-term climatic records for comparison of long-term soil hydrology with soil hydromorphology. Lindbo et al. (Chapter 6) explore the use of quantitative measurements of soil color in epipedons as an approach to correlate soil color to hydrology. While some techniques do not prove useful, others show promise.
Two of the studies [Hobson and Dahlgren (Chapter 7) and Calmon et al. (Chapter 8)] examine hydromorphological relationships in soils with relatively impermeable subsoils. In an examination of vernal pools, Hobson and Dahlgren show low chroma depletions and other hydromorphic features to be well correlated with low redox potentials for episaturation above duripans and clay-enriched soil horizons. Calmon et al. examine soils with fragipans and describe hydromorphic features at depths below the observed high water table. The occurrence of saturated conditions without hydromorphic features is attributed to the short duration of saturation when soil temperatures are cool and to low soil organic carbon levels.
Griffin et al. (Chapter 9) examine the spatial variability of hydromorphic features due to microtopography in a depression and mound landscape and demonstrate that micro-topography had a profound effect on hydrology and soil morphology. Similarly, Tangr ty within “pedon-sized” areas along hillslopes that suggests that soil classification may be inconsistent within a small complex pedon.
Two studies explore the use of soil micromorphological features as indicators of soil hydrology. Rabenhorst and Lindbo (Chapter 11) described dark organic matter in association with mineral soil grains that becomes more prevalent with increasing duration of saturation for sandy coastal plain sediments. For soils of the Willamette Valley of Oregon, Lynn and Austin (Chapter 12) show disseminated or fine particulate manganese(iron) to be present in the matrix, but absent from pores and channels suggesting reduction and depletion in these flow zones.
Whether hydromorphic features have formed under current or previous conditions is a key consideration when using soil morphology to infer current hydrology. West et al. (Chapter 14) describe redoximorphic features occurring higher in the profile than would be suggested by the depth and duration of seasonal water tables on the summits and back-slopes in the Atlantic Coastal Plain. They speculate that redoximorphic features at these locations are related to previous climatic or landscape conditions and do not represent contemporary conditions. Similarly, Greenberg and Wilding (Chapter 13) compare contemporary soil hydrology with morphology and conclude that redoximorphic features associated with contemporary hydrology have diffuse boundaries and relict features have sharp boundaries.
This publication presents the work of a number of scientists from across the country who have recently undertaken to link soil morphology with hydrological parameters. This is not a definitive work. There is much research presently underway by these as well as many others, which as it comes to light will continue to elucidate the complexities of the hydropedological system. We hope that the data and conclusions contained herein will aid researchers, practitioners and regulators as they work to build a quantitative framework for interpreting soil hydromorphology.
MARTIN RABENHORST, coeditor
University of Maryland
College Park, Maryland
JAY BELL, coeditor
University of Minnesota
St. Paul, Minnesota
PAUL MCDANIEL, coeditor
University of Idaho
Will Austin, Faculty Research Assistant, Department of Crop and Soil Science, Oregon State University, Agriculture and Life Sciences Bldg. Room 3035, Corvallis, OR 97331–7306
E.R. Blood, Associate Scientist, J. W. Jones Ecological Research Center, Newton, GA 31770
M.A. Calmon, Postdoctoral Associate, Agricultural and Biological Engineering Dept., University of Florida, Gainesville, FL 32611–0570
Edward J. Ciolkosz, Professor, Dept. of Agronomy, 452 Agricultural Sciences and Industries Building, Pennsylvania State University, University Park, PA 16802–3504
R.A. Dahlgren, Professor, Dept. of Land, Air, & Water Resources, University of California, Davis, CA 95616–8627
W. Lee Daniels, Professor, Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061–0404
Rick L. Day, Assistant Professor, Dept. of Agronomy, 450 Agricultural Sciences and Industries Building, Pennsylvania State University, University Park, PA 16802–3504
Delvin S. Fanning, Professor, Dept. of Natural Resource Sciences, HJ. Patterson Hall, University of Maryland, College Park, MD 20742–5821
L. Peter Galusky, Jr. Corporate Health Environment and Safety, Marathon Oil Company, 539 S. Main St., Findlay, OH 45840
Michael H. Genthner, Soil-Environmental Scientist, 12 Sutton Court, Amherst, MA 01002
Wendy A. Greenberg, Research Assistant, Dept. of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843–2474
Richard W. Griffin, Assistant Professor, CARC, Prairie View A and M University, P.O. Box 4079, Prairie View, TX 77446–4079
Velva A.L. Groover, Research Associate, Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061–0404
Robert L. Hill, Associate Professor, Dept. of Natural Resource Sciences, H.J. Patterson Hall, University of Maryland, College Park, MD 20742–5821
W.A. Hobson, Graduate Research Assistant, Dept. of Land, Air, & Water Resources, University of California, Davis, CA 95616–8627
R.L. Hodges, Instructor, Dept. of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061–0404
Wayne H. Hudnall, Professor, Department of Agronomy, M.B. Sturgis Hall, Louisiana State University, Baton Rouge, LA 70803–2110
L.K. Kirkman, Assistant Scientist, J.W. Jones Ecological Research Center, Newton, GA 31770
David L. Lindbo, Assistant Professor, Dept. of Soil Science, North Carolina State University, Vernon G. James Research and Extension Center, 207 Research Station Road, Plymouth, NC 27962
Warren C. Lynn, Research Soil Scientist, USDA, Natural Resources Conservation Service, National Soil Survey Center, Federal Building Room 152, 100 Centennial Mall North, MS 41, Lincoln, NE 68508–3866
Steve Nagle, Research Specialist, Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061–0404
Gary W. Petersen, Professor, Dept. of Agronomy, 444 Agricultural Sciences and Industries Building, Pennsylvania State University, University Park, PA 16802–3504
Karen Prestegaard, Associate Professor, Dept. of Geology, Rm. 0214A, Chemistry Building, University of Maryland, College Park, MD 20742–4211
Martin C. Rabenhorst, Professor, Dept. of Natural Resource Sciences, H.J. Patterson Hall, University of Maryland, College Park, MD 20742–5821
F.E. Rhoton Soil Scientist, USDA-ARS, National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655
Joey N. Shaw, Assistant Professor, Department of Agronomy and Soils, Auburn University, 202 Funchess Hall, Auburn, Alabama 36849
L.A. Spokas, Research Assistant, Dept. of Plant and Soil Sciences, 19 Stockbridge Hall, University of Massachusetts, Amherst, MA 01003
Susan M. Starowitz, ERM Southwest Inc., 16300 Katy Freeway, Suite 300, Houston, TX 77094–1611
Mark H. Stolt, Assistant Professor, Dept. of Natural Resources Science, University of Rhode Island, Woodward Hall, Kingston, RI 02881–0804
Ariel A. Szögi, Soil Scientist, USDA, Agricultural Research Service, Coastal Plains Soil, Water and Plant Research Center, 2611 West Lucas Street, Florence, SC 29501–1241
Sara A. Tangren, Vice President, Environmental Sciences Corporation, 326 Boyd Avenue, Takoma Park, MD 20912.
P.J. Thomas, Senior Research Associate, Dept. of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061–0404
Peter L.M. Veneman, Professor, Dept. of Plant and Soil Sciences, 19 Stockbridge Hall, University of Massachusetts, Amherst, MA 01003
Larry T. West, Associate Professor, Dept. of Crop and Soil Sciences, Miller Plant Sciences Bldg., University of Georgia, Athens, GA 30602–7272
Larry P. Wilding, Professor, Dept. of Soil & Crop Sciences, Texas A & M University, College Station, TX 77843