
The salinity of marsh water depends largely upon the tides, but 
is also influenced by fresh water flow from upland sources and by rainfall. 
It ranges from nearly or greater than sea-water strength to varying degrees 
of brackishness. 
In the study area, as in much of the Atlantic Coast marshland, 
saltmarsh cordgrass (Spartina alterniflora) is the prevailing plant. It 
is particularly dominant throughout the extensive outer zone bordering the 
bay. Along the margins of creeks and ditches it attains a taller, more 
luxuriant growth. An inner, slightly higher. and better-drained zone is 
covered largely by saltmeadow cordgrass (Spartina patens), along with smaller 
amounts of saltgrass (Distichlis spicata) and blackrush (Juncus gerardi). 
On creek banks and other elevated places, marshelder (Iva frutescens) and 
groundselbush (Baccharis halimifolia) are likely to be found. Saltwort 
(Salicornia spp.) occurs on flats that are subject to intermittent shallow 
inundation; and the excellent duck-food plant, widgeongrass (Ruppia maritima) 
grows in some of the large clear ponds. Various algae are also present 
in some ponds. 
Tidal Movements 
The profound influence of tides upon the organisms inhabiting the 
salt marsh was of importance in population studies. Rivers and creeks 
subject to typical tidal forces alternately flow and ebb twice in each 
lunar day, the average period between successive high and low tides being 
somewhat over 6 hours. In the bays adjoining the study area, the mean 
range between high and low water is about 3.6 feet while near the time of 
full and new moon this increases to a maximum of |}. feet. Species such 
as fish, shrimp, blue crab, etc. move with the tide and their numbers in 
the marsh rise and fall accordingly. 
Tidal movement is likewise an important factor in determining the 
severity of mortality from DDT. Spraying at low tide results in less 
dilution of DDT. Although the numbers of animals subjected to the hazard 
of poisoning are at a minimum at this time, they are crowded into a smaller 
volume of water where the chances for contact are greater. At high tide 
the reverse situation exists. The possibilities of contact with an individual 
animal are lessened but at the same time more animals are present within 
the sprayed area. It would appear that spray applied at high tide would 
be washed out more quickly than a low-tide treatment. In view of these 
facts, the timing of DDT applications in relation to tides becomes an 
important consideration in determining the extent of harm resulting from 
marsh spraying. 
