Three definitions of wetlands are currently used in the United States: the 1977 USACE definition, the Natural Resources Conservation Service definition (1985 FSA definition), and the 1979 FWS definition, as derived from Cowardin et al. (1979). The USACE and FSA definitions have direct regulatory significance through implementation of the CWA and FSA. The 1979 FWS definition, although not directly regulatory, is also significant because it captures the perspective of a federal agency that interacts constantly with the regulatory agencies, comments on permits, and is charged with reporting to Congress on the status of the nation's wetlands.

The 1977 USACE definition references the importance of inundation and saturation—hydrologic conditions—as the prime determinant of wetland status. This definition also cites vegetation as a critical indicator of the hydrologic conditions that lead to the formation of wetlands. Although it refers to soil, it does not indicate that the physical and chemical condition of soil (or, more properly, substrate) is a critical criterion for distinguishing wetlands from other environments.

In referring specifically to soil, the 1977 USACE definition implies that wetlands cannot be supported on nonsoil substrates. Although most wetlands do form on soils and are specifically associated with hydric soils, a few types occupy substrates that are nonsoil or nonhydric soil (Chapter 5). Another difficulty is the specific reference to vegetation, which is commonly interpreted to mean vascular plants. For most regions of the United States, this is a reasonable approach, but some regional wetland types lack vascular plants entirely and instead show their wetland status through the presence of algae, mosses, and even invertebrates that require the basic hydrologic conditions associated with saturation or inundation of the substrate (Chapter 5). Finally, the 1977 USACE definition does not make sufficiently clear that wetlands are ecosystems, i.e., functionally integrated systems that reflect the hydrologic conditions leading to their formation.

The FSA definition emphasizes the importance of hydric soil as a critical indicator of wetland status. It implies that wetlands cannot exist without hydric soils. The vast majority of wetlands do in fact have hydric soils, and they can be identified by the presence of hydric soils in the absence of hydrologic alterations. Some wetlands do, however, develop on substrates that are not now classified as hydric soil (Chapter 5). Given that the FSA definition of wetlands was intended for application to agricultural areas, the emphasis on hydric soil is understand-

FRONT MATTER (R1-R20)

EXECUTIVE SUMMARY (1-12)

1 INTRODUCTION AND BACKGROUND (13-19)

2 ECOLOGY OF WETLAND ECOSYSTEMS (20-42)

3 WETLAND DEFINITIONS: HISTORY AND SCIENTIFIC BASIS (43-64)

4 WETLAND DELINEATION: PAST AND CURRENT PRACTICE (65-89)

5 WETLAND CHARACTERIZATION: WATER, SUBSTRATE, AND BIOTA (90-148)

6 ESPECIALLY CONTROVERSIAL WETLANDS (149-167)

7 REGIONALIZATION (168-189)

8 MAPS, IMAGES, AND MODELING IN THE ASSESSMENT OF WETLANDS (190-206)

9 REGULATION OF WETLANDS: ADMINISTRATIVE ISSUES (207-214)

10 FUNCTIONAL ASSESSMENT OF WETLANDS (215-226)

REFERENCES (227-252)

APPENDIXES (253-296)

INDEX (297-306)

LIST OF PUBLICATIONS (307-308)