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estuary, other economically important species such as shrimp, clam, 
blue crab, and oyster could not exist without its supply of nutrients 
and its protected waters. 
The salt marsh serves man in other ways besides supplying most 
of the seafood that is consumed by him. Its resiliency serves as a 
buffer zone that protects the upland against disastrous flooding and 
erosion. The marsh is a natural safety valve that dissipates the energy 
of storm waves before they can damage coastal structures and crop- 
land. The marsh vegetation acts as a sediment trap and contributes 
to the settling out of suspended material. If the marsh is destroyed, 
sediment normally deposited here becomes available for deposition 
in channels, harbors, and other navigable areas. Hence, marsh destruc- 
tion intensifies silting problems elsewhere. 
In summary, the marshes add a fringe to the continent and form a 
feature of great ecological and economic magnitude. High productivity 
is maintained by— 
1. The ebb and flow of tidal action which serves to transport 
nutrients. 
2. An abundant supply of nutrients. 
3. Rapid regeneration and conservation of nutrients due to 
the activities of micro-organisms and filter feeders. 
4. Three types of primary producers (marsh grass, mud algae, 
and phytoplankton) that insure maximum utilization of sunlight 
in all seasons. 
5. Constant, year-round production of plant material. 
This high level of production is naturally maintained by a dynamic 
system of continuous interactions, and the effects of man on these 
interactions generally leads to a general deterioration of the marsh’s 
functions. 
In spite of man’s general attitude that wetlands were fit only for 
dumping, human effects on them were unimportant until the 20th 
century. The great expansion of power production, increased industrial 
activity, increased movement in navigable waters, higher fishing 
intensity, and more sewage discharged into natural waters all have 
combined to put strains on the estuarine system. It may be noted here 
that one-third of the U.S. population lives and works close to an 
estuary. The estuarine ecosystem is a limited vital resource and 
decisions concerning the use of this resource are not now made in a 
rational manner. To date, man’s effects on the marshes have been 
unimaginative, poorly planned, and frequently destructive. Many 
uses are served by the wetland-estuary system and the system is 
under ever-increasing pressure from many sources, Intelligent manage- 
ment is imperative, but for this to be realized, more basic research 
is needed to produce facts upon which to base rational decisions (fig. 
V). Human influences on the marshes fall into the following categories: 
1. Modification of river influx, resulting in salinity changes. 
2. Organic enrichment, mainly through the discharge of munic- 
ipal wastes. 
3. Addition of heated waters from powerplants. 
4. Alteration of the drainage system. 
5. Addition of noxious compounds such¥as industrial wastes, 
pesticides, and oil. 
