-TEMPERATURE 



Modified from Gameson 

 and Griffith, 1959 



I I I 



20 24 



4 8 12 16 



TIME - DAY 



SIX MONTH AVERAGE DIURNAL CURVES 



rOR RIVER H\l, ENGLAND 



Figure U 



centimeters. Here, however, with a much lower 

 phytoplankton population, the oxygen production 

 rate never exceeded 1 gram per square meter per 

 hour for the period studied . 



The quantity of oxygen produced by photo- 

 plankton can be both impressive and important. In 

 raw sewage stabilization ponds in the northern part 

 of the country, production of as much as 26 grams 

 per square meter per day by a biological system 

 using 19 grams per square meter per day for total 

 respiration (a P/R of 1 .4) assures a favorable oxy- 

 gen balance during illuminated periods. It also 

 provides a surplus that can be mixed by wind and 

 convection currents into deeper, less illuminated 

 strata so that they also can participate in aerobic 

 stabilization. Some dissolved oxygen persists in- 

 to the night, but usually it is completely used be- 

 fore the next period of illumination . Although the 

 quantities of oxygen in question may seem small, 

 the customary daily addition to these ponds of 

 oxygen-demanding material in the form of sewage 

 is only about 1-1/4 grams per square meter. Even 

 in rivers, unless their pollution load is unusually 

 heavy, an oxygen production rate of 7 .4 grams per 

 square meter per day and respiratory rate of 5 grams 

 per square meter per day (P/R of 1 .5) , as found in 

 the Ohio River, leave a surplus sufficient for the 

 usual total demand . 



Both in sewage stabilization ponds and in 

 streams, surplus oxygen produced by phytoplankton 

 is not efficiently used and may be unavailable for 



oxidizing organic matter within a short time bfter it 

 is produced. During periods of intense oxygen pro- 

 duction the water becomes supersaturated and oxy- 

 gen escapes to the atmosphere. Surface agitation 

 by wind accelerates such loss as suggested by the 

 lower oxygen concentrations in stabilization ponds 

 on windy days than on calm days {Figure 8) . In 

 quiescent, organically rich waters such as these, 

 oxygen concentration decreases rapidly with depth, 

 but in rivers with their constant movement, such 

 gradients are rare. Nocturnal oxygen depletion 

 through continued intense respiration may become 

 serious - more so in ponds than in rivers. 



While no one disclaims the importance of 

 photosynthetic oxygen, the present state of knowl- 

 edge does not show how such oxygen may be uti- 

 lized more efficiently. The whole subject of phyto- 

 plankton in relation to oxygen production and use 

 has not yet reached a state of development permit- 

 ting practical application to the analysis of oxygen 

 resources or use in the oxygen sag equation. Even 

 when data are available on momentary rates of photo- 

 synthesis in relation to phytoplankton density, light 

 intensity, limits of the euphotic zone, and other 

 factors , it is not clear how such data can be ap- 

 plied to practical problems . There is need for 

 wider and more intensified study in this area. Also, 

 there is need to relate photosynthetic potential of 

 the waters to some numerical expression of the phy- 

 toplankton, whether this is given as pigment con- 

 centration, number of cells per volume, packed cell 



60 



