Similarly, parts of high marsh soils may become aerated during periods 

 of dry weather and low water tables. 



Most sediments, such as freshly deposited dredged materials, will be 

 highly anaerobic or low in oxygen. However, this does not prevent the 

 establishment of adapted marsh species. These plants have various 

 adaptations to an anaerobic environment. For example, certain intertidal 

 species have anatomical features that enable their leaves to supply oxy- 

 gen to their roots (Teal and Kanwisher, 1966; Anderson, 1974; Kasapligil, 

 1976). Smooth cordgrass and probably many others utilize ammonia, 

 which is the usual form of nitrogen under anaerobic conditions, more 

 efficiently than the nitrate form, usually preferred by upland species 

 (Gosselink, 1970; Woodhouse, Seneca, and Broome, 1976; Mendelssohn, in 

 preparation, 1979). 



Some intertidal species contribute to the aeration of soils by re- 

 leasing oxygen from their roots. This has been demonstrated for Pacific 

 cordgrass under controlled conditions and in the field (Pride and Lingle, 

 1976; Wong, 1976). The evidence of it in the form of oxidized (yellow- 

 ish or brown) zones around the roots and rhizomes of smooth cordgrass 

 has been frequently observed. Oxygen supplied in this way promotes the 

 activity of other organisms and eventually contributes to improved 

 internal drainage and increased aeration. From a practical marsh-build- 

 ing point of view, the scarcity of oxygen in marsh soils appears to be 

 unimportant. There is no evidence that it will prevent the establish- 

 ment of marsh plants on sites that are otherwise suitable. Anaerobic 

 conditions affect the growth of marsh plants by favoring the maintenance 

 of nitrogen in the ammonia form and promoting the availability of such 

 elements as iron and manganese by maintaining them in a reduced form. 

 There probably are detrimental effects but little is known about them. 

 Iron toxicity may occur because of the excessive availability of this 

 element under highly anaerobic conditions. Similar effects may occur 

 with other elements or compounds but these have not limited marsh 

 creation. 



Some dredged materials contain toxic substances that may interfere 

 with plant growth and will need to be covered with uncontaminated mate- 

 rial for marsh planting. Marsh areas may be underlain by "cat clays" 

 (clays which are high in reduced sulphur) (Gallagher, Plumley, and Wolf, 

 1977). These become extremely acid through th.e oxidation of the sul- 

 phur when exposed to the atmospkere. Dredged material of this type, 

 placed above mean sea level (MSL) , must be covered with other soil to 

 permit plant growth. 



IV. MARSH PLANTS 



1. Kinds and Adaptations . 



A wide variety of plants can grow under marshy conditions where 

 the water is fresh or only mildly brackish. This report emphasizes 



29 



