surface saturation averaged 81. 5 percent and the bot 

 torn 72 5 percent. In spite of these differences the 

 figures are of such similar order as to point to the same 

 general conclusion that the lake possesses a high de- 

 gree of oxygen saturation. 



The oxygen content from station to station 

 throughout the lake. June -September, may be seen at 

 a glance in figures 31-34. At nearly every station the 

 surface saturation was above that at the bottom. In 

 June there was a low oxygen content occurrence near 

 Buffalo; surface and bottom saturation ran around 60 

 percent. Rarely did the surface saturation ever drop 

 below 90 percent. The bottom, however, was al- 

 most always less saturated than the surface. That the 

 bottom water, shut off from direct contact with the 

 atmosphere and in many cases below the photic zone, 

 did not run even lower in its oxygen content suggests 

 that there may be relatively little organic decom- 

 position in the lake. The lowest oxygen concentra- 

 tion usually occurred in regions of considerable depth, 

 where presumably there was less chance for vertical 

 mixing as well as photosynthetic activity because of 

 lower light intensity and the lower temperatures char- 

 acteristic of the hypolimnion. 



Supersaturation was observed at about one-half 

 meter below the surface. In June there was a super- 

 saturated area in the western part of the lake. Super- 

 saturation occuned during July and September m the 

 surface waters of the Long Point region (figs 25 and 

 26) To be sure the figures never ran very high, loa 

 percent being the maximum for July. Active photo- 

 synthesis probably produced the high oxygen content. 

 In this region, too. there are currents which may 

 have affected a certain amount of vertical mixmg ot 

 the stratum so that with rise in temperature, there 

 may have resulted a certain amount of supersaturation. 



The lowest oxygen saturation in the open -lake 

 waters was found at the bottom in August at two 

 western stations. 41 and 42. where the percent sat- 

 uration dropped to 44 and 52 respectively. At all 

 other times and places reduction in the oxygen of bot- 

 tom waters in the western area and in the region of 

 the Deep Hole off Long Point usually ran between bO 

 and 70 percent. The areas of oxygen concentration 

 below 81 percent near the bottom may be seen in 

 figure 29. Further discussion of the variations m oxy- 

 gen will be made in connection with the treatment of 

 carbon dioxide. 



The oxygen saturation of Lake Erie has not 

 shown great extremes. Its supersaturation does not 

 anywhere approach the figures obtained in certain 

 other lakes, such as Lake Mendota where Birge and 

 Juday(1911) found 150 percent saturation a common 

 condition in the epilimnion. On the other hand, 

 its bottom oxygen reduction does not approach that 

 for Lake Mendota where the bottom water may be- 

 come void of oxygen in July. Lake Erie would seem 

 to approximate more nearly an entirely different 

 type of lake, such as Cayuga in central New York 

 State The waters of this lake showed in July, 1927. 

 a satilration of 104. 1 percent at the surface and 83.4 

 percent at the bottom where the depth was 63 meters 

 (Burkholder 1931). 



The oxygen conservation in Lake Erie appears to 

 be due to the general oUgotrophic character of the 

 body of water. Photosynthetic activity apparently 

 never reaches a peak sufficient to highly supersaturate 

 the epilimnion. Its processes of decomposition are only 

 moderate in amount and hence the hypolimnion does 

 not dip to a minimum oxygen content such as is found 

 in lakes richer in organic materials. 



Carbon Dioxide 



The dissolved carbon dioxide of natural waters is 

 of importance chiefly because of its effect upon the 

 alkaline reserve and the pH of the environment, and 

 because it is a raw material used in photosynthesis 

 The sources of carbon dioxide are: (1) the atmosphere 

 which contains 3 parts per 10, 000-. (2) the processes 

 of fermentation and decomposition in the lake; and 

 (3) drainage from the watershed. When the free car- 

 bon dioxide is exhausted, the algae have recourse to 

 the half -bound carbon dioxide and in this way draw 

 upon the bicarbonates. This situation is present m 

 the epilimnion of Lake Erie, since in both the summe, 

 of 1928 and in 1929 no free carbon dioxide was found 

 in samples taken near the surface. In the bottom 

 waters, however, free carbon dioxide occurred fre- 

 quently. 



In the tables and discussion, the carbon dioxide 

 figures are presented in two forms, the positive and 

 the negative carbon dioxide. The positive carbon 

 dioxide is the actual &ee dissolved carbon dioxide 

 present, expressed as parts per million. The negativ 

 carbon dioxide is an expression of the amount of car- 

 bon dioxide which would have to be added to convert 



76 



