Oxygen Pulse in Eagle Lake 311 



THE DIURNAL OXYGEN PULSE IN EAGLE (WINONA) 



LAKE. 



Will Scott, Indiana University. 



This paper presents data which demonstrates an observable oxygen 

 pulse in the surface water of Eagle (Winona) Lake when the weathei 

 is clear and relatively calm. 



When a lake stratifies after the vernal overturn, the hypolinmion 

 is sealed from the air and the respiration of the organisms and the 

 decay of the organic matter gradually reduce the amount of oxygen 

 present in this stratum. In the epilimnion the water may be circulated 

 by the wind and consequently any part of it may be exposed to the 

 air and may take up oxygen or give it up depending on the amount it 

 contains. The upper levels of this region receive most of the light ab- 

 sorbed, so that photosynthesis is more pronounced at these levels than 

 deeper. 



In the epilimnion the amount of dissolved oxygen may be increased 

 by absorption from the surface and by photosynthesis. It may be 

 decreased by discharge at the surface, by respiration of organisms, and 

 by the decay of organic matter. All of these factors that influercs the 

 amount of dissolved oxygen are continuous except photosynthesis. It 

 occurs only in sunlight and consequently is diurnal on clear days. 



So long as the amount of oxygen remains below the saturaticn 

 point, it is difficult to establish the combination of factors which is re- 

 sponsible for the amount observed. However, when the water becomes 

 saturated, as it often does in calm weather, it can be accounted for only 

 by photosynthesis, modified slightly by temperature changes. 



In building up high supersaturation, the increase must occur all in 

 one day, or there must be a series of daily rises, or there must be a di- 

 urnal rise and fall in the amount of dissolved oxygen. This would be 

 more marked near the surface on calm days. On windy days the water 

 in Eagle Lake is mixed to such a depth (five meters in Eagle Lake) 

 that the effect of photosynthesis is obscured. 



Observations were made at two stations, a littoral and a pelagic. 

 The littoral station was in an embayment just offshore from the Bio- 

 logical Station. This bay was filled with aquatic phanerogams, chiefly 

 Potamogetons and the accompanying biota. The pelagic station was 

 about 100 meters beyond this in the open water. The oxygen was de- 

 termined by the Winkler method. The water was collected by means of 

 a 100 cc. pipette and discharged into rubber stoppered bottles until an 

 amount equal to the capacity of the bottle was flushed. The water 

 was treated and titrated at once. The water was always collected 

 within a few centimeters of the surface. 



Two types of observations were made. One consisted of collections 

 made at 9:30 a. m. and 4:15 p. m. The second type consisted of serial 

 collections running as near 24 hours as the lake remained calm. These 

 were very difficult to get complete. The lake might be perfectly calm 

 in the morning and after a few samples had been taken the wind would 

 disturb conditions so that the series would have to be discontinued. 



"Proc. Ind. Acad. Sci., vol. 33. 1923 (1924)." 



