24 



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. Department of Interior National 

 Atlas 1970:110-111 for generalized regional delin- 

 eation). 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 development 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 

 surface water is absent, the water table is usually at or 

 very near the land surface. 



Seasonally Flooded. Surface water is present for 

 extended 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 

 exposed, but surface water is present for variable 

 periods without detectable seasonal periodicity. 

 Weeks, months, or even years may intervene between 

 periods of inundation. The dominant plant com- 

 munities under this regime may change as soil mois- 

 ture conditions change. Some areas exhibiting this 

 regime do not fall within our definition of wetland 

 because they do not have hydric soils or support 

 hydrophytes. 



Artificially Flooded. The amount and duration of 

 flooding is controlled by means of pumps or siphons in 

 combination 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 manage- 

 ment 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, therefore, 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 fresh- 

 water habitats are further subdivided by pH levels. 



Salinity Modifiers 



Differences in salinity are reflected in the species 

 composition of plants and animals. Many authors have 

 suggested 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 seawater 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. 



We have modified the Venice System, suggested at a 

 "Symposium on the Classification of Brackish 

 Waters" in 1958, for use in the Marine and Estuarine 

 systems (Table 2). The system has been widely used 

 during recent years (Macan 1961, 1963; Burbank 1967; 

 Carriker 1967; Reid and Wood 1976), although there 

 has been some criticism of its applicability (den 

 Hartog 1960; Price and Gunter 1964). 



The salinity of inland water is dominated by four 

 major cations, calcium (Ca), magnesium (Mg), sodium 

 (Na), and potassium (K); and three major anions, car- 

 bonate (C0 3 ), sulfate (S0 4 ), and chloride (CI) (Wetzel 

 1975). Salinity is governed by the interactions between 

 precipitation, surface runoff, groundwater flow, evap- 



