Modifying terms applied to the classes or subclasses are essential for use of the system. In tidal 

 areas, the type and duration of flooding are described by four water regime modifiers: subtidal. 

 irregularly exposed, regularly flooded, and irregularly flooded. In nontidal areas, six regimes are 

 used: permanently flooded, intermittently exposed, semipermanently flooded, seasonally flooded, 

 saturated, temporarily flooded, intermittently flooded, and artificially flooded. A hierarchical 

 system of water chemistry modifiers, adapted from the Venice System, is used to describe the 

 salinity of the water. Fresh waters are further divided on the basis of pH. Use of a hierarchical 

 system of soil modifiers taken directly from U.S. soil taxonomy is also required. Special modifiers 

 are used where appropriate: excavated, impounded, diked, partly drained, farmed, and artificial. 



Regional differences important to wetland ecology are described through a regionalization that 

 combines a system developed for inland areas by R. G. Bailey in 1976 with our Marine and 

 Estuarine provinces. 



The structure of the classification allows it to be used at any of several hierarchical levels. 

 Special data required for detailed application of the system are frequently unavailable, and thus 

 data gathering may be prerequisite to classification. Development of rules by the user will be 

 required for specific map scales. Dominance types and relationships of plant and animal com- 

 munities to environmental characteristics must also be developed by users of the classification. 

 Keys to the systems and classes are furnished as a guide, and numerous wetlands and deepwater 

 habitats are illustrated and classified. The classification system is also compared with several 

 other systems currently in use in the United States. 



The U. S. Fish and Wildlife Service conducted an 

 inventory of the wetlands of the United States (Shaw 

 and Fredine 1956) in 1954. Since then, wetlands have 

 undergone considerable change, both natural and man- 

 related, and their characteristics and natural values 

 have become better defined and more widely known. 

 During this interval. State and Federal legislation has 

 been passed to protect wetlands, and some statewide 

 wetland surveys have been conducted. 



In 1974 the U.S. Fish and Wildlife Service directed 

 its Office of Biological Services to design and conduct 

 a new national inventory of wetlands. Whereas the 

 single purpose of the 1954 inventory was to assess the 

 amount and types of valuable waterfowl habitat, the 

 scope of the new project is considerably broader (Mon- 

 tanari and Townsend 1977). It will provide basic data 

 on the characteristics and extent of the Nation*s 

 wetlands and deepwater habitats and should facilitate 

 the management of these areas on a sound, multiple- 

 use basis. 



Before the 1954 inventory was begun, Martin et al. 

 (1953) had devised a wetland classification system to 

 serve as a framework for the national inventory. The 

 results of the inventory and an illustrated description 

 of the 20 wetland types were published as U. S. Fish 

 and Wildlife Service Circular 39 (Shaw and Fredine 

 1956). This Circular has been one of the most common 

 and most influential documents used in the continuous 

 battle to preserve a critically valuable but rapidly 

 diminishing national resource (Stegman 1976). 

 However, the shortcomings of this work are well 

 known (e.g., see Leitch 1966; Stewart and Kantrud 

 1971). 



In attempting to simplify their classification, 

 Martin et al. (1953) not only ignored ecologically criti- 

 cal differences, such as the distinction between fresh 

 and mixosaline inland wetlands but also placed dis- 

 similar habitats, such as forests of boreal black spruce 



{Picea mariana) and of southern cypress-gum (Taxo- 

 dium distiehum-Nyssa aquatica) in the same category, 

 with no provisions in the system for distinguishing be- 

 tween them. Because of the central emphasis on water- 

 fowl habitat, far greater attention was paid to vege- 

 tated areas than to nonvegetated areas. Probably the 

 greatest single disadvantage of the Martin et al. 

 system was the inadequate definition of types, which 

 led to inconsistencies in application. 



Numerous other classifications of wetlands and 

 deepwater habitats have been developed (Stewart and 

 Kantrud 1971; Golet and Larson 1974; Jeglum et al. 

 1974; Odum et al. 1974; Zoltai et al. 1975; Millar 1976), 

 but most of these are regional systems and none would 

 fully satisfy national needs. Because of the weaknesses 

 inherent in Circular 39, and because wetland ecology 

 has become significantly better understood since 1954, 

 the U. S. Fish and Wildlife Service elected to construct 

 a new national classification system as the first step 

 toward a new national inventory. The new classifi- 

 cation, presented here, has been designed to meet four 

 long-range objectives: (1) to describe ecological units 

 that have certain homogeneous natural attributes; (2) 

 to arrange these units in a system that will aid deci- 

 sions about resource management; (3) to furnish units 

 for inventory and mapping; and (4) to provide uni- 

 formity in concepts and terminology throughout the 

 United States. 



Scientific and common names of plants (Appendix 

 A) and animals (Appendix B) were taken from various 

 sources cited in the text. No attempt has been made to 

 resolve nomenclatorial problems where there is a taxo- 

 nomic dispute. Many of the terms used in this classifi- 

 cation have various meanings even in the scientific lit- 

 erature and in some instances our use of terms is new. 

 We have provided a glossary (Appendix C) to guide the 

 reader in our usage of terms. 



