250 



community and stimulate excessive populations of individual 



species to nuisance conditions. 

 The entire ecosystem may be stressed by thermal pollution. The 

 amount of damage is dependent on the resulting temperature of the 

 environment and the species composition of the biotic community. 

 The total range of detriments should be carefully considered on an 

 individual case basis before heat is released to the environment. 



SEDIMENTATION 



The estuarine zone serves as a repository for the susx^ended material 

 carried by the Nation's rivers. From a pure mass standpoint, a signifi- 

 cant percentage of these materials is comprised of the sediment load 

 which is measured in billions of tons annually. For example, a conserva- 

 tive estimate of the sediment from the Mississippi River through its 

 delta complex is 500 million tons annually. 



Man's activities may purposely or inadvertently upset the natural 

 balance of inflow, deposition, and outflow. If upstream erosion is 

 increased due to poor land-management practlices, the load carried 

 in suspension will increase. Conversely, activities along the coast can 

 result in increased shore erosion, removing more sediment than is con- 

 tributed. The primary pollutional problem from sediment, however, 

 results from increased influx and accelerated deposition. 



The detrimental effects of sedimentation are reflected in an impair- 

 ment of uses such as navigation, recreation, water supply, and fish 

 propagation. Navigational interests are damaged by the accretion of 

 materials in ship channels and near docking facilities; millions of 

 dollars are expended each year in channel dredging to maintain navi- 

 gation. Recreational interests suffer from the loss of safe boating 

 water, increased maintenance of marinas, and from the loss of fishing 

 areas (fig. IV.5.8). The cost of diversion and use for water supply 

 purposes may be significantly increased because of the need to remove 

 excess sediment. 



Fishery loss stems from the destruction of suitable habitat. This 

 damage results from loss of suitable breeding areas, loss of food chain 

 organisms because of change in benthic characteristics, and fish kills 

 from excessive turbidity. 



Channel maintenance adds to the sedimentation problem. The cost 

 of dredging is greatly influenced by the selection of spoil areas; 

 if the spoil is redeposited in the water environment, changes in bottom 

 characteristics are transferred to other areas, thus expanding the 

 scope of impact. Dredging spoil disposal results in increased tur- 

 bidities as well as changing bottom configuration. Both occurrences 

 can adversely affect the aquatic habitat. Natural sedimentation is an 

 integral part of the estuarine environment. Manmade sedimentation 

 problem is a form of pollution that is significant in terms of dollar 

 damages and must be considered in the overall management scheme. 



CATASTROPHIC ACCIDENTS 



One great threat to the estuarine ecosystem is the ever-present 

 chance of a catastrophic spill of oil or other hazardous materials. The 

 large volumes of petroleum and chemical products transported 



