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; per- 

 manently flooded areas are considered deepwater habitats 

 in these Systems. The boundary between wetland and 

 deepwater habitat in the Riverine and Lacustrine 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 emer- 

 gent plants normally grow (Welch 1952; Zhadin and Gerd 

 1963; Sculthorpe 1967). As Daubenmire (1968:138) stated, 

 emergents are not true aquatic plants, but are "amphib- 

 ious," growing in both permanently 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 Dominance 

 Types. Figure 1 illustrates the classification structure to 

 the class level. Table 1 lists the Classes and Subclasses 

 for each System and Subsystem. 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 deepwater 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, chemical, or biological fac- 

 tors. We further subdivide Systems into more specific 

 categories called subsystems. 



The characteristics of the five major Systems— Marine, 

 Estuarine, Riverine, Lacustrine, and Palustrine— have 

 been discussed at length in the scientific literature and 

 the concepts are well recognized; however, there is fre- 

 quent disagreement as to which attributes 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 asso- 

 ciated 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 fresh- 

 water 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 emer- 

 gents, trees, or shrubs; or (3) the seaward limit of the 

 Estuarine System, where this limit is determined by fac- 

 tors other than vegetation. Deepwater habitats lying 

 beyond the seaward limit of the Marine System are out- 

 side 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 substrate; (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. 

 Subtidal.— The substrate is continuously submerged. 

 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 fresh- 

 water runoff from the land. The salinity may be periodical- 

 ly increased above that of the open ocean by evaporation. 

 Along some low-energy coastlines there is appreciable dilu- 

 tion of sea water. Offshore areas with typical estuarine 

 plants and animals, such as red mangroves (Rhizophora 



