PLANKTON IN WATER SUPPLY MEIER 399 



stream at the end of a bright sunny day where the food-manu- 

 facturing activities of the algae have progressed at maximum rate, 

 the oxygen eliminated by the plants loads the water beyond the 

 point of saturation. At night when there is no sunlight, and photo- 

 synthesis or food manufacture ceases, the plants use a considerable 

 amount of the oxygen thrown off during the day for respiration. 

 Thus both the animal and plant life in the water are making de- 

 mands on the available oxygen supply. When sewage or large 

 quantities of decomposing organic matter present in the water make 

 an increased demand on the oxygen supply, the nightly reduction 

 in oxygen becomes serious. This is especially true when, owing to 

 continued cloudy weather during the day, the oxygen supply is de- 

 creased and the water does not contain sufficient oxygen to last the 

 night. When there is sewage pollution in a shallow body of water 

 with little circulation, the oxygen is completely used up and the fish 

 are exterminated. An extensive growth of blue-green or yellow- 

 green algal bloom or scum is generally observed in ponds or lakes 

 where high oxygen concentration occurs. 



Thus it may be seen that when the proper balance between the 

 amount of sunlight, concentration of plants, and number of fish in 

 a pond is upset by cutting down the light so that the plants cannot 

 perform their photosynthesis, they then enter into competition with 

 the fish for oxygen, or the balance may be upset by an increase in 

 plant organisms, or the fish may upset the balance by destroying the 

 plants. 



THE pH 



The active acidity of a solution is usually indicated by the negative 

 logarithm of the normal concentration denoted by the sign pH, the 

 hydrogen ion exponent. The concentration of the hydrogen ions at 

 neutral reaction is denoted by pH=7. As pH is a negative logarithm, 

 the lower the designation of the pH, the higher the concentration of 

 hydrogen ions and the more acid is the reaction. Organisms usually 

 grow in a solution with a pH of 6 to 8.5. 



TASTES AND ODORS IN THE WAT-ER SUPPLY 



The most familiar way in which algae make their presence known 

 to us in the home is by their taste and odor so affecting the pota- 

 bility of the water that it is impossible to use it for drinking pur- 

 poses. Consumers often prefer to drink water from private wells 

 and springs, which may be of questionable sanitary quality, if they 

 consider that their municipal water supply has an unpleasant odor 

 or taste. The senses of taste and smell, although intimately asso- 

 ciated, are distinct. Salt, for example, has a ver}^ definite taste but 



