substances in solution-particularly nitrates and 

 phosphates. Such minerals are a normal constit- 

 uent of land drainage and are also present in 

 highly concentrated form in domestic, industrial, 

 and agricultural wastes returned to streams. Prob- 

 lems from algae blooms and excessive plant growth 

 are increasingly troublesome in many of the 

 nation s major lakes and effective remedial meas- 

 ures are largely lacking. 



4) Organic chemicals such as insecticides, pesti- 

 cides, and detergents. These substances are highly 

 toxic at very low concentrations. They have 

 caused spectacular kills of fish and wildlife. Of 

 particular concern is our lack of knowledge of the 

 effects of long-term and sublethal exposure. At 

 present, prospects appear poor for developing 

 methods either of effective treatment or of re- 

 moval of the substances from water supplies. 



5) Other minerals and chemicals. Included in this 

 group of industrial wastes are chemical residues, 

 petrochemicals, salts, acids, silts, and sludges. 

 Some 400-500 new such chemical substances are 

 created for use each year. Many are known to be 

 toxic although full knowledge of their exact 

 biological effects is lacking. Methods of removal 

 are poorly developed. 



6) Sediments from land erosion. Settleable and 

 suspended solids resulting from land erosion fill 

 stream channels and reservoirs, necessitate expen- 

 sive additional treatment of water supplies, reduce 

 a stream 's ability to assimilate oxygen-demanding 

 wastes, blanket fish nests and food organisms and 

 tend to mask out the light required by aquatic 

 plants. 



7) Radioactive substances. Intense public concern 

 has led to the successful development of tech- 

 niques to prevent contamination under present 

 conditions. The anticipated large increase in nu- 

 clear power reactors by the year 2000 poses a 

 serious additional challenge, however. 



8) Heat from power and industrial plants. Since 

 the amount of dissolved oxygen that water can 

 contain decreases with increasing water tempera- 

 ture, introducing heat into a stream has an effect 

 equivalent to that of introducing oxygen consum- 

 ing waste. 



III. POLLUTION PRESSURES 



Even as we write, pressures continue to mount, 

 which increase the pollution problem. Some of 

 these noted in chapters 2 and 3 include: 



-Rapidly increasing population. The demand for 

 water within the next 50 to 60 years will triple 

 while the population doubles. The increased per 

 capita use of water will be caused by increased 

 urbanization and industrialization; rising levels of 

 income; and increased leisure and outdoor recrea- 

 tion. Rising demand also involves requirements for 

 higher quality water than we have today. 



-Greater mining of sand and gravel and possibly 

 phosphates from off-shore locations. As we indi- 

 cated earlier (Chapter 2), although there are ample 

 land-based deposits of sand and gravel for con- 

 struction purposes, the cost of carrying these 

 deposits to urban areas is high. In addition, the 

 movement to "Keep America Beautiful" is tending 

 to close down some of the sand and gravel pits 

 near large cities. Consequently, off-shore deposits 

 of these materials have become very attractive 

 when they are close to metropolitan areas. 



—Increased desalting of estuarine and coastal 

 waters as technology improves, creating brine, heat 

 and radioactive waste disposal problems. 



—Increased housing and commercial sites in estu- 

 aries, causing fiUing-in of marshes and bays, runoff 

 of urban debris, and soil erosion. Commercial and 

 private housing development was marked as the 

 second major cause of the loss of estuarine areas; 



Figure 3. Massive oil spills from the tanker 

 Ocean Eagle off San Juan, Puerto Rico. (U.S. 

 Coast Guard photo) 



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