THE EFFECT OF POLLUTION ON RIVER ALGAE 



C. Mervin Palmer 



U. S. Department of Health, Education, and Welfare, Public Health. Service, 

 Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio 



A large majority of algae are affected adversely by the gross pollution of 

 streams with organic wastes such as domestic sewage. After partial self-purifi- 

 cation of the stream has occurred, however, the populations and kinds of algae 

 become much more numerous than are present in the clean portion of the 

 stream above the area of pollution. This increase is due to the nutrients that 

 are made available from the decomposing organic wastes. 



The undecomposed organic wastes affect the algae by causing chemical and 

 physical changes in the stream. Increased turbidity reduces the light availa- 

 ble for photosynthesis. Increased organic content in the water stimulates 

 saprophytic and saprozoic organisms which then compete for space with the 

 algae. Certain constituents of the waste are toxic to many algae. Thus, 

 many factors of the environment that are changed by the organic wastes have 

 an effect on the algae. 



Information on the physiological and morphological effects of organic pollu- 

 tion on algae is very limited at present. There have been, however, many 

 studies of the change in the algal tlora as a result of pollution. Gross pollu- 

 tion causes a great reduction in the number of kinds of algae in the stream. 

 Those able to remain have frequently been called "indicators" of pollution, 

 but no specific kinds individually are reliable indicators of grossly polluted 

 water. Polluted water varies too much to ensure an environment satisfactory 

 for the growth or persistence of any one particular algal species. Any indi- 

 vidual species tolerant of pollution may also be found in unpolluted areas of a 

 stream or may be absent in some areas of pollution. 



When a number of the tolerant genera and species are considered, it becomes 

 likely that a high percentage of these will be present in all areas of streams 

 grossly polluted with organic wastes. The presence of such a community of 

 algae in a stream, therefore, is a reliable indicator of the condition of the water. 



Many workers have listed the genera and species of algae found in polluted 

 waters, particularly in the United States and in Europe. The number of 

 kinds which they have considered to be pollution tolerant is generally quite 

 limited for any one area or survey, but becomes very large when all of the 

 results of many investigators are combined. 



The lists of pollution-tolerant algae reported by 110 workers have been ex- 

 amined by the writer to date. The genera and species of algae tolerant to 

 sewage or to related conditions have been recorded, and a total of more than 

 600 species and varieties has been compiled. 



To tabulate the information, the writer has allotted arbitrary numerical 

 values to each author's record of an alga. A value of 2 was given to each 

 alga reported as very highly tolerant, and a value of 1 to each alga highly tolerant 

 to the presence of organic matter. Lightly tolerant and nontolerant algae 

 were not recorded in the compilation. The total points from all of the 110 



389 



