6 BULLETIlsr 960, U. S. DEPAETMENT OF AGRICULTURE, 



In this connection the source from which the water is drawn or the 

 character of the soil in the reservoir is important. The water of a 

 lake with a muck bottom and swampy margin has generally a lower 

 oxygen content than one with a sand or gravel bottom. The studies 

 of Birge and Juday (2) show that this applies to Wisconsin lakes and 

 the studies of one of the writers (Bergman) have shown that the 

 oxygen content of water from cedar-swamp reservoirs in Massachu- 

 setts was only 10 to 40 per cent of that in clear pond water at the same 

 time. For the same reason, the water of reservoirs constructed on 

 marshes is usually low in oxygen content. 



The influence of light intensity on the oxygen content of flooding 

 water and its relation to the water injury of submerged cranberry 

 plants has been considered in another paper (1). Briefly, it may be 

 stated that whereas the process of respiration, in which oxygen 

 is taken up from the water by the submerged plant, goes on both in 

 light and in darkness, the process of photosynthesis, in which oxygen 

 is given off to the water by the plant, can take place only in the 

 light. On a clear day the oxygen content of the water on a flooded 

 cranberry marsh in growing condition increases. On the other 

 hand, at night or in cloudy weather the oxygen content of the water 

 is reduced, and if the cloudiness persists for two or three days the 

 oxygen content may become very low and injury may result. 



OXYGEN CONTENT OF WATERS USED IN FLOODING CRANBERRY 



MARSHES IN WISCONSIN. 



During September of the years 1918 and 1919 determinations of 

 the oxygen content of more than 130 samples of water from various 

 marshes in Wisconsin were made. Winkler's titrimetric method for 

 determining the oxygen content of water (10, p. 2843) was used in 

 all cases. 



From these analyses, of which Table II gives a few typical examples, 

 it is evident that the oxygen content of the flooding water of Wis- 

 consin cranberry marshes is generally below saturation. In some 

 cases the deficiency is very marked. This is due to the fact that in 

 practically all cases the water is held in reservoirs constructed on 

 marshes. 



These analyses show that the oxygen content of water in reservoirs 

 and on the flooding sections of marshes increases during the day and 

 that the increase is greater on clear days than on cloudy ones. This 

 is illustrated by the analyses of reservoir water at Black River Falls 

 on September 10 and 11, 1919. On September 10, a cloudy day, the 

 oxygen content of the water at the north end of the reservoir increased 

 from 3.22 c. c. per liter at 11.30 a. m. to 3.74 c. c. per liter at 

 4.45 p. m. On September 11, a clear day, the oxygen content of the 



