industrial waste . 



Provision of Dissolved Oxygen 



In relation to water quality management, the 

 most valuable contribution of phytoplankton is pro- 

 vision of oxygen for use in oxidation by the total 

 aerobic biota. Oxygen is vitally important because 

 it affects the capacity of streams to receive and 

 oxidize sewage and other organic wastes without 

 unduly impairing water quality. Multiple use of 

 water resources is increasingly necessary as 

 water-hungry population and industries grow while 

 the total water supply remains constant. Use of 

 water for waste disposal presently is inescapable. 

 It is therefore appropriate to point out some of the 

 fundamental oxygen relationships related to waste 

 disposal. Aside from the natural cyclic effects of 

 phytosynthesis by aquatic plants, significant 

 changes in the dissolved oxygen content of a 

 stream result primarily from the oxidation of or- 

 ganic matter entering as waste. A combination of 

 available dissolved oxygen and suitable biota - 

 especially aerobic bacteria - results in progres- 

 sive oxidation and stabilization of the organic mat- 

 ter. It has been postulated (Streeter and Phelps, 

 1925) that the rate of biochemical oxidation of or- 

 ganic matter is proportional to the remaining con- 

 centration of unoxidized substance measured in 

 terms of oxidizability. Unpolluted water tends to 

 hold in solution the maximum amount of oxygen it 

 is capable of holding at the existing temperature 

 and partial oxygen pressure of the atmosphere, but, 

 when organic pollutants are introduced, use of the 

 dissolved oxygen supply in progressive satisfac- 

 tion of the demand tends to reduce the oxygen con- 

 tent below this saturation value. Sources of oxy- 

 gen available for this use are (l) that initially dis- 

 solved in the water, (2) that absorbed from the at- 

 mosphere by partially deoxygenated water, and 

 (3) oxygen made available through photosynthesis 

 of aquatic plants . These interrelations are shown 

 graphically in a recent publication (Bartsch and 

 Ingram, 1959) . At present, our interest is directed 

 to the last oxygen source only. 



Equations have been developed and used 

 widely to elucidate the dynamics involved in the 

 oxygen resources of streams (Streeter and Phelps, 

 1925) . Although others have taken a modified ap- 

 proach and added refinements to evaluating these 

 relations, photo synthetic oxygen production, un- 

 fortunately, has remained elusive of precise quan- 

 titative expression as a part of the over-all pic- 

 ture . That photosynthesis in aquatic plants af- 

 fects dissolved oxygen levels in surface waters 

 has been known for a long time . General relation- 

 ship of photosynthesis to stream sanitation, how- 

 ever, is a more recent interest. Studies of 

 Potomac River plankton and rooted plants in 1913 



by Purdy (Gumming, 1916) included measurement of 

 oxygen changes caused by photosynthesis. The 

 importance of plant-covered flats below the Dis- 

 trict of Columbia in accelerating recovery from 

 pollution originating at that point is discussed at 

 some length. Oxygen production in one area was 

 shown to be 17.7 pounds per acre per day, mainly 

 by submerged aquatic plants growing on flats out- 

 side the river channel . 



Calvert (1933) studied diurnal fluctuations of 

 dissolved oxygen in the White River below the 

 Indianapolis sewage treatment plant in relation to 

 varying B.O.D. load and amount of sunshine. 

 Daytime oxygen concentrations frequently reached 

 5 or 6 ppm . but usually dropped to zero at night, 

 showing the importance of algal photosynthesis in 

 maintaining a daytime supply of dissolved oxygen 

 and preserving desirable aerobic conditions . 



Since the early observations cited , diurnal 

 variations in dissolved oxygen have been noted 

 and reported many times . Typical variations are 

 shown in Figure 1 for two stations on French Creek 

 near Meadville, Pennsylvania, where a study was 

 made in August, 1955 , to determine stream condi- 

 tions and assimilation capacity characteristics. 

 Obviously, monetary oxygen data, such as might 

 be obtained by sampling as chance and conven- 

 ience bring the technician and the stream together, 

 have little value in showing stream character. If 

 station A had been sampled only at 5:00 p.m. , the 

 early morning depression would have been missed; 

 if sampled only at 8:00 a.m., the period of super- 

 saturation would not have been detected . The sit- 

 uation would have been the same at station O but 

 the differences less pronounced. Sampling defi- 

 ciencies such as these are discussed thoroughly by 

 Gameson and Griffith (1959) . It is obvious that 

 stream technicians cannot properly discern oxygen 

 conditions in surface waters by restricting them- 

 selves to field sampling and analyses only during 

 the usual working hours between 8 and 5 . 



Newly developed equipment that automati- 

 cally analyzes and records dissolved oxygen 

 (Macklin, Baumgartner, and Ettinger, 1959) now 

 makes collection of diurnal data both less tedious 

 and more accurate. Desired oxygen data are now 

 obtainable with less nocturnal sampling under the 

 adverse conditions of darkness . Figure 2 shows 

 dissolved oxygen records for a two-day period ob- 

 tained with such equipment at an experimental 

 sewage stabilization pond. The record for both 

 days shows dissolved oxygen was absent at sun- 

 rise. Factors affecting photosynthesis and oxygen 

 retention by the water obviously were more favor- 

 able on November 19 than November 14 according 

 to dissolved oxygen levels attained. The periodic 

 irregularities resulted from variation in illumina- 

 tion . It is sometimes taken as a "rule of thumb" 

 in reference to algal photosynthesis that the higher 

 the oxygen level climbs above saturation in the 



57 



