WEATHER IN CRANBERRY CULTURE 9 



suit of these processes are usually relatively small and of short duration since 

 there is nearly always enough wind to cause circulation of the water and thus keep 

 it at or near its oxygen saturation capacity. But when the water is covered with 

 ice, circulation by the wind is prevented and, since convection currents are rel- 

 atively ineffective and diffusion is extremely slow, the amount of dissolved oxygen 

 in the water surrounding the vines is determined by the respiratory and photo- 

 synthetic activity of the vines and other plants usually present. 



The most abundant plants on a cranberry bog, of course, are the cranberry 

 vines, but other green plants, particularly mosses and algae, sometimes aid very 

 materially in reducing or increasing the oxygen content of the water. In addition, 

 bacteria and other microorganisms which are always present where there is organic 

 matter act to reduce the oxygen content since they use oxygen in respiration but 

 do not carry on photosynthesis. 



The density of vine growth, the abundance of moss or algae, and the amount of 

 organic matter in the soil on different bogs or on different parts of the same bog 

 vary greatly. This makes little difference in the dissolved oxygen content of 

 water under ice so long as conditions are favorable for photosynthesis, since the 

 amount of oxygen given off equals or exceeds that used by respiration, and 

 consequently the oxygen content of the water either remains nearly the same or 

 increases from day to day. However, under conditions which greatly retard or 

 prevent photosynthesis, excessive vine growth or a dense growth of moss or algae 

 is objectionable because more oxygen is used in respiration, thus increasing the 

 probability of injury to the vines. 



Under conditions unfavorable for photosynthesis, the dissolved oxygen content 

 of the water is reduced more rapidly on bogs on which there is a great amount of 

 organic matter. The probable reason for this is that the greater the amount of 

 organic matter the greater the number of bacteria and other microorganisms 

 associated with it, and the greater the amount of oxygen used in respiration. 

 Organic matter is found on all bogs since either peat or muck usually makes up a 

 large part of bog soils, and dead leaves make up most of the surface litter. Less 

 organic matter comes in direct contact with the water on sanded bogs than on 

 those not sanded. Therefore, the probability of a complete disappearance of the 

 dissolved oxygen in water under ice, when conditions are unfavorable for photo- 

 synthesis, is greater on a peat bog that has never been sanded, or has not been 

 sanded for several years, than on one sanded regularly at intervals of three or 

 four years; it is least on bogs with "hard bottom." 



The rate of respiration of plants on a flooded bog is influenced by the tempera- 

 ture of the water. Photosynthesis, likewise, is affected by temperature but also 

 by other factors. Both respiration and photosynthesis go on slowly at 32° F., 

 and the rate of both increases as the temperature rises. The temperature of the 

 water under ice on a winter-flooded bog has a definitely limited range, however, 

 varying from 32° to 39°, and changes slowly, rarely more than one degree within 

 24 hours. 



The rate of photosynthesis is determined not only by the temperature of the 

 water, but also by the concentration of carbon dioxide in solution, and by the 

 intensity of the light received by the vines. The concentration of carbon dioxide 

 in solution in water on flooded bogs not covered by ice is about the same as in 

 the air, but in water under ice it is always greater than in the air. Photosyn- 

 thesis goes on more rapidly as the intensity of the light increases although its 

 rate is limited also by the temperature. 



The intensity of the light received by cranberry vines on a winter-flooded bog 

 depends on the intensity of the incident light, the thickness and clearness of the 

 ice, the presence or absence of snow on the ice, and the depth and clearness of the 

 water under the ice. The intensity of the light received at the surface of a bog 



