8 MASS. EXPERIMENT STATION BULLETIN 402 



water and to keep it In equilibrium with the oxygen of the air. Convection cur- 

 rents, however, are usually slower and much less effective than those set up by 

 the action of wind. 



The action of wind on the water of a flooded bog sets the surface water In 

 motion producing currents which carry small masses of surface water, saturated 

 with oxygen, below the surface. If the dissolved oxygen content of the surface 

 water when it is carried downward is different from that of the water below the 

 surface, oxygen passes by diffusion from the water with the greater amount of 

 oxygen in solution to the water with less. Water from below also is brought to 

 the surface where the oxygen in solution quickly comes to equilibrium with the 

 oxygen of the air. This process continues until the entire mass of water is brought 

 to a uniform dissolved oxygen content. 



The effectiveness of wind in equalizing the distribution of dissolved oxygen 

 in the water of a flooded bog depends on Its velocity. The stronger the wind, the 

 more rapidly the mixing proceeds and the greater the depth to which it extends. 

 When the wind stirs the water to the depth to which bogs ordinarily are flooded, 

 any local excess or deficiency of dissolved oxygen In the water below the surface 

 is leveled out. It is to the rapidity with which oxygen diffuses into or out of the 

 surface laj'er of water that circulation of the water by action of the wind, and by 

 convection currents, owes most of its effectiveness in bringing the dissolved oxygen 

 of the water to an equilibrium with the oxygen of the air. 



A local excess or deficiency of dissolved oxygen in the water of a flooded bog 

 may occur in the absence of wind or with wind of low velocity. An oxygen con- 

 tent below the saturation capacity of the water has often been found on flooded 

 bogs. The deficit is greater in deep water, but no evidence has been obtained to 

 indicate that on winter-flooded bogs not covered with Ice the deficit ever becomes 

 so great as to Injure the vines. The occurrence of an oxygen deficit, at a depth 

 of only two to three feet, when there is little or no wind, shows that convect'on 

 currents and diffusion are not sufficient, even in relatively shallow water, to keep 

 the dissolved oxygen in equilibrium with the oxygen of the air. An excess of 

 dissolved oxygen under these conditions has never been found. 



Biological Factors 



Biological factors are those that owe their effect to physiological processes 

 carried on by living organisms. Two of these, respiration and photosynthesis, 

 affect the dissolved oxygen content of the water on flooded bogs and sometimes 

 cause great variations on it. 



Respiration is the term applied to a complex oxidation process taking place in 

 every living cell, by which chemical energy is released for the performance of the 

 physiological processes necessary to maintain life. In nearly all plants the energy 

 is released b}- the oxidation of carbohydrates and fats into carbon dioxide and 

 water. The process requires oxj-gen, which normally Is obtained from the air 

 outside the plant, and carbon dioxide Is given off. 



Photosynthesis occurs onlj in plants or parts of plants that contain the green 

 coloring matter known as chlorophyll and only when they are exposed to light. 

 It is the process by which sugars and starch are formed. Carbon dioxide and 

 water are used in the process, and oxygen is given off. The sugars and starch 

 thus formed are used subsequently in respiration to supply energy to the plants. 



The oxygen used in respiration by the cranberry vines and other plants on a 

 flooded bog is taken from that in solution in the water and the oxygen given off in 

 photosynthesis goes into solution in it. Consequently, respiration reduces the 

 amount of dissolved o.xygen and photosynthesis increases it. However, when a 

 bog is not covered with ice, changes in the oxygen content of the water as a re- 



