flooded or saturated at some time each year and land 

 that is not. 



The boundary between wetland and deepwater 

 habitat in the Marine and Estuarine systems coincides 

 with the elevation of the extreme low water of spring 

 tide; permanently flooded areas are considered deep- 

 water habitats in these systems. The boundary be- 

 tween wetland and deepwater habitat in the Riverine, 

 Lacustrine, and Palustrine systems lies at a depth of 

 2 m (6.6 feet) below low water; however, if emergents, 

 shrubs, or trees grow beyond this depth at any time, 

 their deepwater edge is the boundary. 



The 2-m lower limit for inland wetlands was selected 

 because it represents the maximum depth to which 

 emergent plants normally grow (Welch 1952; Zhadin 

 and Gerd 1963; Sculthorpe 1967). As Daubenmire 

 (1968:138) stated, emergents are not true aquatic 

 plants, but are "amphibious," growing in both perma- 

 nently flooded and wet, nonflooded soils. In their 

 wetland classification for Canada, Zoltai et al. (1975) 

 also included only areas with water less than 2 m deep. 



THE CLASSIFICATION SYSTEM 



The structure of this classification is hierarchical, 

 progressing from systems and subsystems, at the 

 most general levels, to classes, subclasses, and domi- 

 nance types. Figure 1 illustrates the classification 

 structure to the class level. Table 1 lists the classes 

 and subclasses for each system and gives an example 

 of a dominance type for each subclass. Artificial keys 

 to the systems and classes are given in Appendix E. 

 Modifiers for water regime, water chemistry, and soils 

 are applied to classes, subclasses, and dominance 

 types. Special modifiers describe wetlands and deep- 

 water habitats that have been either created or highly 

 modified by man or beavers. 



Hierarchical Structure 



Systems and Subsystems 



The term SYSTEM refers here to a complex of 

 wetlands and deepwater habitats that share the 

 influence of similar hydrologic, geomorphologic, chem- 

 ical, or biological factors. We further subdivide 

 systems into more specific categories called 



SUBSYSTEMS. 



The characteristics of the five major systems- 

 Marine, Estuarine, Riverine, Lacustrine, and Palus- 

 trine— have been discussed at length in the scientific 

 literature and the concepts are well recognized; how- 

 ever, there is frequent disagreement as to which attri- 

 butes should be used to bound the systems in space. 

 For example, both the limit of tidal influence and the 

 limit of ocean-derived salinity have been proposed for 



bounding the upstream end of the Estuarine System 

 (Caspers 1967). As Bormann and Likens (1969) pointed 

 out, boundaries of ecosystems are defined to meet 

 practical needs. 



Marine System 



Definition. The Marine System (Fig. 2) consists of 

 the open ocean overlying the continental shelf and its 

 associated high-energy coastline. Marine habitats are 

 exposed to the waves and currents of the open ocean 

 and the water regimes are determined primarily by the 

 ebb and flow of oceanic tides. Salinities exceed 30 %o, 

 with little or no dilution except outside the mouths of 

 estuaries. Shallow coastal indentations or bays 

 without appreciable freshwater inflow, and coasts with 

 exposed rocky islands that provide the mainland with 

 little or no shelter from wind and waves, are also 

 considered part of the Marine System because they 

 generally support typical marine biota. 



Limits. The Marine System extends from the outer 

 edge of the continental shelf shoreward to one of three 

 lines: (1) the landward limit of tidal inundation 

 (extreme high water of spring tides), including the 

 splash zone from breaking waves; (2) the seaward limit 

 of wetland emergents, trees, or shrubs; or (3) the 

 seaward limit of the Estuarine System, where this 

 limit is determined by factors other than vegetation. 

 Deepwater habitats lying beyond the seaward limit of 

 the Marine System are outside the scope of this 

 classification system. 



Description. The distribution of plants and animals 

 in the Marine System primarily reflects differences in 

 four factors: ( 1 ) degree of exposure of the site to waves; 

 (2) texture and physicochemical nature of the sub- 

 strate; (3) amplitude of the tides; and (4) latitude, 

 which governs water temperature, the intensity and 

 duration of solar radiation, and the presence or 

 absence of ice. 



Subsystems. 



Subtidai— The substrate is continuously sub- 

 merged. 



Intertidal.— The substrate is exposed and flooded 

 by tides; includes the associated splash zone. 



Classes. Rock Bottom, Unconsolidated Bottom, 

 Aquatic Bed, Reef, Rocky Shore, and Unconsolidated 

 Shore. 



Estuarine System 



Definition. The Estuarine System (Fig. 3) consists of 

 deepwater tidal habitats and adjacent tidal wetlands 

 that are usually semienclosed by land but have open, 

 partly obstructed, or sporadic access to the open 

 ocean, and in which ocean water is at least occasionally 

 diluted by freshwater runoff from the land. The salin- 

 ity may be periodically increased above that of the 



