Fig. 3. Distinguishing features and examples of habitats in the Estuarine System. EHWS 

 tides; ELWS = extreme low water of spring tides. 



extreme high water of spring 



end where the concentration of ocean-derived salts in 

 the water exceeds 0.5%o during the period of annual 

 average low flow, or where the channel enters a lake. It 

 terminates at the upstream end where tributary 

 streams originate, or where the channel leaves a lake. 

 Springs discharging into a channel are considered part 

 of the Riverine System. 



Description. Water is usually, but not always, 

 flowing in the Riverine System. Upland islands or 

 Palustrine wetlands may occur in the channel, but 

 they are not included in the Riverine System. Palus- 

 trine Forested Wetlands, Emergent Wetlands, 

 Scrub-Shrub Wetlands, and Moss-Lichen Wetlands 

 may occur adjacent to the Riverine System, often on a 

 floodplain. Many biologists have suggested that all 

 the wetlands occurring on the river floodplain should 

 be a part of the Riverine System because they consider 

 their presence to be the result of river flooding. 

 However, we concur with Reid and Wood (1976:72,84) 

 who stated, "The floodplain is a flat expanse of land 

 bordering an old river. . . . Often the floodplain may 

 take the form of a very level plain occupied by the 



present stream channel, and it may never, or only occa- 

 sionally, be flooded. ... It is this subsurface water [the 

 ground water] that controls to a great extent the level 

 of lake surfaces, the flow of streams, and the extent of 

 swamps and marshes." 



Subsystems. The Riverine System is divided into 

 four subsystems: the Tidal, the Lower Perennial, the 

 Upper Perennial, and the Intermittent. Each is defined 

 in terms of water permanence, gradient, water veloc- 

 ity, substrate, and the extent of floodplain develop- 

 ment. The subsystems have characteristic flora and 

 fauna (see lilies and Botosaneau 1963; Hynes 1970; 

 Reid and Wood 1976). All four subsystems are not 

 necessarily present in all rivers, and the order of occur- 

 rence may be other than that given below. 



Tidal. —The gradient is low and water velocity fluc- 

 tuates under tidal influence. The streambed is mainly 

 mud with occasional patches of sand. Oxygen deficits 

 may sometimes occur and the fauna is similar to that 

 in the Lower Perennial Subsystem. The floodplain is 

 typically well developed. 



Lower Perennial.— The gradient is low and water 



