364 



J. E. Hobbieet al. 



Results 



The respiration of the sediment varied greatly from sample to sample. 

 Replicates had a coefficient of variation of 50% (range was 4 to 390%). 

 Because of this variation, the respiration rates of a series of samples 

 collected along a transect across pond A (Figure 8-6) were not statistically 

 different. The increased respiration in the zone of rooted plants is obvious, 

 however. 



Most of the respiration in the plant-free areas of the pond takes place 

 in the top few centimeters of sediment. For example, when the top 4 cm of 

 sediment were removed there was an average reduction of 77% in the 

 respiration rates (four experiments). As noted earlier (Table 8-1), the 

 bacteria also decreased greatly in the top 4 cm and it is likely that the fungi 

 are confined entirely to the top few centimeters because of their need for 

 oxygen. In addition, 99.6% of the algae and 89% of the chironomids were 

 found in the top 4 cm. 



During a single day the respiration rate varied with the temperature at 

 the sediment surface; however, the wave of diffusion of CO 2 from below 

 the surface layer lags behind and correlates with the temperature wave 

 within the sediment. As measured in the water above the surface of the 

 sediment (Figure 8-7), the maximum respiration occurred between 1300 

 and 1900 and coincided with the temperature peak but not with the peak of 

 solar radiation. However, the respiration increased at 0400 in the morning 

 at a time when the surface layers were still cooling. It is likely that CO2 

 from below the sediment surface is diffusing upward in waves 

 corresponding to the temperature oscillations within the sediment. At 10 



■E 

 o30 



o> 



E 



15 





0-1 



20 



15 



10 



a. 



E 

 w 



A. Solar radiation 



B. Benthic respiration 



C. Temp, at sediment surface 



D. Temp, at 10 cm in sediment 



- 50 



24 



08 



16 20 



Time, t\rs 



FIGURE 8-7. Benthic respiration, solar respiration, and temperature in 

 Pond B on 24 and 25 July 1972. 



