Chemistry 93 



dissolved CO2 would be only 0.37 mg C liter"'. A PCO2 of 640 ppm 

 equals 0.74 mg CO2-C liter ' in this pond. 



The data are expressed as the gradient of the partial pressures of CO2 

 between the water and the air (Figures 4-9, 4-10). Because the PCO2 in air 

 was constant at 320 ppm, the actual pCOo in the water is equal to the 

 gradient plus 320. 



The water in the pond was supersaturated with CO 2 with respect to 

 air throughout the period of sampling. This implies that there is a transfer 

 of CO 2 from the water to the air. There must be an excess of respiration 

 over photosynthesis in the ponds; this respiration is mostly taking place in 

 the sediments (Chapter 8). Another implication is that despite the constant 

 turbulence of the water in the ponds, the transfer rate of CO 2 is relatively 

 slow so that the pond's CO 2 is not in equilibrium with the atmosphere. 

 Over the period of the pond measurements, approximately the middle half 

 of the open water season, the gradient averaged 397 ppm (Table 4-6). 



The water of the shallow lake was also supersaturated with CO 2 

 (Figure 4-10) but the mean gradient was only one-third that found in the 

 ponds (Table 4-6). The record of CO 2 for the lake spans the entire ice-free 

 season and includes meltwater on top of the bottom-fast ice in the spring 

 and several spot measurements of CO2 beneath the ice in the fall. In part 



TABLE 4-6 The PCO2 and Related Factors in Pond C (1971) and North 

 Meadow Lake (1972) 



Parameter Pond Lake 



Seasonal mean CO2 gradient 397 ±185 ppm 115 ±83 ppm 



(water minus air) 



Maximum mean daily 923 ± 208 ppm 306 ±47 ppm 



CO2 gradient 



Maximum instantaneous 1217 ppm 404 ppm 



CO2 gradient 



Maximum instantaneous 1530 ppm 722 ppm 



PCO2 



Minimum instantaneous 136 ppm -32 ppm 



CO 2 gradient 



Seasonal mean temperature 2.5 ±3.4 C 4.0±3.5 C 



Water 



Seasonal mean temperature 7.1 ±3.5 C 7.0±3.1 C 



Sediment 

 Seasonal m£an wind speed 



399 ± 139cm sec ^ 409 ± 174cm sec" 



