167 
Some of the mechanisms through which land activities affect the 
estuarine environment are poorly understood. Many activities remove 
the natural vegetation from the land. This results in increased runoff 
and thus increased fresh water flow into the estuarine system. Agri- 
culture, road construction, and urban development all affect the 
estuarine circulation and the distribution of water properties through 
increased runoff. Artificial regulation of streamflow will also alter 
imputs of fresh water, particularly seasonal inflow. Impoundment of 
water in a reservoir may change chemical and thermal properties. 
Runoff, particularly from agricultural land, contains nutrients leached 
from the soil, and pesticides. These constituents directly affect water 
quality. Another class of activities introduces quantities of sediment 
into estuarine systems, affecting both water quality and estuarine 
form. Urban development, construction agriculture and mining fall 
in this category. It should be noted that the form of an estuary can 
be changed by direct means—filling, dredging, etc.—or by sedimenta- 
tion. The process of sedimentation is complex, but intimately con- 
nected with the circulation. Thus a change in form through sedimenta- 
tion can result from a change in circulation, or from increased sediment 
loads in the water. All the secondary changes in form listed in table IL 
result from increased sedimentation, either as a result of circulation or 
increased sediment in the water, not as direct alteration of form. 
The direct effects of estuarine and watershed activities listed in 
table II are obvious. Discharge of toxic substances, heat or wastes 
will affect water quality. Generally these discharges are a result of 
urbanization or industrialization in the estuarine area. Dredging, 
construction and landfill operation in the estuary will affect estuarine 
form. Finally, construction, dredging and mining will affect estuarine 
circulation and sedimentation. 
CONCLUSIONS 
Estuaries are a valuable resource. An estuary can be described with 
three parameters. Land uses in the watershed of an estuary and in 
the estuary itself should be examined to see whether they will affect 
any of these parameters. This procedure should reduce the number of 
land use—estuary interactions which are overlooked when planning 
land use. The more difficult problem of determining the specific 
effect on the estuarine environment due to specific changes in these 
parameters must still be studied. 
BIBLIOGRAPHY 
Cronin, Eugene L. ‘‘Role of Man in Estuarine Processes,” Estuaries, ed. by 
G.H. Lauff. American Association for the Advancement of Science Publica- 
tion 83. Baltimore Md.: Horn Schaffer Co., 1967. p. 667-689. 
Federal Water Quality Administration, U.S. Department of Interior. National 
Estuarine Pollution Study. Washington, D.C.: U.S. Government Printing 
Office, 1970 (Senate Document 91-58). 
Pritchard, D. W. “What is an Estuary: Physical Viewpoint,’ Estuaries, ed. 
by G. H. Lauff. American Association for the Advancement of Science Publica- 
tion 83. Baltimore, Md.: Horn Schaffer Co., 1967. : : 
Ryther, J. H. ‘Photosynthesis and Fish Production in the Sea,’’ Science, vol. 
166 (Oct. 3, 1969), p. 72-76. | 
Teal, John and Mildred. Life and Death of the Salt Marsh. Boston, Mass.: Little 
Brown and Co., 1969. 
