22 



are usually two unequal high tides and two unequal low 

 tides (mixed semidiurnal). 



Individual tides range in height from about 9.5 m (31 

 feet) at St. John, New Brunswick (U.S. National Oceanic 

 and Atmospheric Administration 1973) to less than 1 m 

 (3.3 feet) along the Louisiana coast (Chabreck 1972). Tides 

 of only 10 cm (4.0 inches) are not uncommon in Louisi- 

 ana. Therefore, though no hard and fast rules apply, the 

 division between regularly flooded and irregularly flooded 

 water regimes would probably occur approximately at 

 mean high water on the Atlantic Coast, lowest level of 

 the higher high tide on the Pacific Coast, and just above 

 mean tide level of the Gulf Coast. The width of the inter- 

 tidal zone is determined by the tidal range, the slope of 

 the shoreline, and the degree of exposure of the site to 

 wind and waves. 



Nontidal 



Though not influenced by oceanic tides, nontidal water 

 regimes may be affected by wind or seiches in lakes. Water 

 regimes are defined in terms of the growing season, which 

 we equate to the frost-free period (see the U.S. Depart- 

 ment of Interior National Atlas 1970:110-111 for gen- 

 eralized regional delineation). The rest of the year is 

 defined as the dormant season, a time when even extended 

 periods of flooding may have little influence on the devel- 

 opment of plant communities. 



Permanently Flooded. Water covers the land surface 

 throughout the year in all years. Vegetation is composed 

 of obligate hydrophytes. 



Intermittently Exposed. Surface water is present 

 throughout the year except in years of extreme drought. 



Semipermanently Flooded. Surface water persists 

 throughout the growing season in most years. When sur- 

 face water is absent, the water table is usually at or very 

 near the land surface. 



Seasonally Flooded. Surface water is present for ex- 

 tended periods especially early in the growing season, but 

 is absent by the end of the season in most years. When 

 surface water is absent, the water table is often near the 

 land surface. 



Saturated. The substrate is saturated to the surface for 

 extended periods during the growing season, but surface 

 water is seldom present. 



Temporarily Flooded. Surface water is present for brief 

 periods during the growing season, but the water table 

 usually lies well below the soil surface for most of the 

 season. Plants that grow both in uplands and wetlands 

 are characteristic of the temporarily flooded regime. 



Intermittently Flooded. The substrate is usually ex- 

 posed, but surface water is present for variable periods 

 without detectable seasonal periodicity. Weeks, months, 

 or even years may intervene between periods of inunda 



tion. The dominant plant communities under this regime 

 may change as soil moisture conditions change. Some 

 areas exhibiting this regime do not fall within our defini- 

 tion of wetland because they do not have hydric soils or 

 support hydrophytes. 



Artificially Flooded. The amount and duration of flood- 

 ing is controlled by means of pumps or siphons in com- 

 bination with dikes or dams. The vegetation growing on 

 these areas cannot be considered a reliable indicator of 

 water regime. Examples of artificially flooded wetlands 

 are some agricultural lands managed under a rice-soybean 

 rotation, and wildlife management areas where forests, 

 crops, or pioneer plants may be flooded or dewatered to 

 attract wetland wildlife. Neither wetlands within or 

 resulting from leakage from man-made impoundments, 

 nor irrigated pasture lands supplied by diversion ditches 

 or artesian wells, are included under this modifier. 



Water Chemistry Modifiers 



The accurate characterization of water chemistry in 

 wetlands and deepwater habitats is difficult, both because 

 of problems in measurement and because values tend to 

 vary with changes in the season, weather, time of day, 

 and other factors. Yet, very subtle changes in water 

 chemistry, which occur over short distances, may have a 

 marked influence on the types of plants or animals that 

 inhabit an area. A description of water chemistry, there- 

 fore, must be an essential part of this classification system. 



The two key characteristics employed in this system are 

 salinity and hydrogen-ion concentration (pH). All habitats 

 are classified according to salinity, and freshwater habitats 

 are further subdivided by pH levels. 



Salinity Modifiers 



Differences in salinity are reflected in the species com- 

 position of plants and animals. Many authors have sug- 

 gested using biological changes as the basis for subdividing 

 the salinity range between sea water and fresh water 

 (Remane and Schlieper 1971). Others have suggested a 

 similar subdivision for salinity in inland wetlands (Moyle 

 1946; Bayly 1967; Stewart and Kantrud 1971). Since the 

 gradation between fresh and hypersaline or hyperhaline 

 waters is continuous, any boundary is artificial, and few 

 classification systems agree completely. 



Estuarine and Marine waters are a complex solution of 

 salts, dominated by sodium chloride (NaCl). The term 

 haline is used to indicate the dominance of ocean salt. The 

 relative proportions of the various major ions are usually 

 similar to those found in sea water, even if the water is 

 diluted below sea water strength. Dilution of sea water 

 with fresh water and concentration of sea water by 

 evaporation result in a wide range of recorded salinities 

 in both surface water and interstitial (soil) water. 



