experimental oiling of Whittaker Creek 

 salt marsh in Chesapeake Bay (Hershner and 

 Lake 1980). This marsh was closed off by 

 natural spits vegetated with marsh plants. 

 When the Spartina was killed on oiled 

 sites, the spits eroded on their exposed 

 sides, although there were no erosional 

 changes in the unoiled sites. 



High tide does not necessarily occur 

 at the same time nor reach the same 

 absolute height above sea level in all 

 parts of a given marsh. Water movement 

 into large marshes is slowed by bottom 

 friction so that high water at the extreme 

 inner portions of the marsh may occur 

 hours later than high water at the edge of 

 the marsh and the sea. The tidal range 

 may differ between the mouth and inner 

 parts of a large marsh. A strong wind 

 blowing into a marsh may hold water in, 

 doing away with normal low tide, while the 

 opposite wind can depress the height of 

 high water. The enormous 7-m tides of 

 northern Maine are naturally less modified 

 by wind than the tiny 30-40 cm tides of 

 the south shore of Cape Cod. The latter 

 are often more controlled by wind than 

 gravity. Typically, south of Cape Cod the 

 tidal range is about 1 m while north of 

 the Cape it is about 3 m. 



Freshwater may enter a marsh through 

 rivers or streams flowing into the upper 

 portions of the marsh, often through a 

 freshwater marsh. In many marshes, at 

 least in New England, there is also 

 significant freshwater input in the form 

 of groundwater entering from the 

 surrounding uplands. This water enters 

 most readily in sandy parts of the marsh 

 (such as creek bottoms). 



2.3 



CHEMICAL ENVIRONMENT 



The chemical environment of salt 

 marshes is dominated by twice-daily 

 flooding with seawater. The environment 

 is saline, even occasionally hypersaline, 

 so that the higher plants (terrestrial in 

 origin) must have mechanisms for dealing 

 with both the water stress of the high 

 osmotic potential and the abundance of 

 sodium chloride and other major components 

 of seawater. Since percolation of water 

 into salt marsh sediments is slow, the 

 interstitial salinity changes less rapidly 



than that of surface water. Therefore, 

 interstitial salinity, the salinity around 

 the plant roots, is often not the same as 

 that of the water flooding the marsh. 



Sediment salinity is also changed by 

 evapotranspi ration. Water evaporates 

 from leaves and the marsh surface, but the 

 salts stay behind, thereby increasing the 

 soil salinity. Sediment salinity may be 

 reduced by the influence of rain or 

 groundwater. 



Tidal waters are the principal source 

 of plant nutrients since seawater contains 

 abundant supplies of calcium, potassium, 

 magnesium, and many other elements 

 essential for plant growth. Nitrogen and 

 phosphorus are exceptions; however, they 

 are the elements which limit plant 

 production in the sea, and we will 

 consider their role in marshes in Section 

 5.3. 



Conditions in the marsh sediments are 

 greatly influenced by the abundance of 

 sulfate in seawater. Under anoxic 

 conditions, there are some bacteria that 

 use sulfate as an electron acceptor, 

 decompose organic matter, and produce 

 sulfide. The resulting sulfide is 

 primarily responsible for the degree of 

 reduction in marsh sediments. Sulfide is 

 highly toxic to most organisms, so those 

 that inhabit marsh sediments must either 

 deal with it or avoid contact with it. 

 Metals, especially iron, are also abundant 

 in marsh sediments, and much of the 

 sulfide produced is bound up as metal 

 sulfides (King 1983; Howarth and Giblin 

 1983). 



Another major factor in the chemical 

 environment of marsh organisms is their 

 exposure to air and sometimes rain during 

 low tide. The higher plants, as far as 

 their leaves are concerned, are 

 terrestrial at low tide. Their leaves are 

 exposed to air and subjected to the same 

 conditions of light, drying, and CO2 

 availability as nearby upland grasses. 

 Marsh animals that can breathe air have an 

 abundant oxygen supply. Gases, which 

 diffuse ten thousand times more rapidly in 

 air than in water, are much more available 

 in the very uppermost layer of the 

 sediments at low tide than at high tide. 

 The extent to which water drains from 



