Chemistry 91 



Coyne and Kelley (1974). Air was circulated in a closed system from a 

 floating cuvette to the IRGA in a hut and then eventually bubbled back to 

 the cuvette via a fritted glass disc located in the water just beneath the 

 cuvette. The dimensions of the cuvette were 30 x 30 x 23 cm. The CO2 in 

 the ambient air was also measured periodically. Both measures are 

 reported in ppm by volume on a dry air basis. Both water and air 

 measurements were compared with reference gases each hour. 



Accuracy of CO2 measurements in the concentration range of air 

 (320 ppm) was approximately ±2 ppm. Pond PCO2 values ranged from 

 450 to over 1,500 ppm. Accuracy of the measurements decreased in 

 proportion to the increase in concentration range and was possibly no 

 better than ±5% at the upper end of the range. 



The PCO2 values in the ponds are always high, yet the actual quantity 

 of CO2 gas dissolved in the water is quite low. This is a result of the low 

 alkalinity and the slightly basic or neutral pH values in the ponds. For 

 example, in early July 1971 the total CO2-C was 4.45 mg liter"' as 

 calculated from alkalinity and pH (Figure 4-8). Most of the C was in the 

 form of HCO3. If the CO2 gas were in equilibrium with the atmosphere, 

 that is at 100% saturation, then the PCO2 would be 320 ppm but the 



14 

 0I2 



,-10 - 



0} 



B 8 

 o 



i 6 



Q. 



E 4 



I I I I I I I I I I I I I I I I I — I I I I I I — rn — I I I I I — I I I I — I I I I 



2 - 



-2 



I I I I I I I I I ' I I ' I ' I ' ' ' I I ' ' ' I ' ' I I I I ^ I I I ' I ' ' 



1000 



800 



E 

 a. 

 a. 



600 



c 

 - 



o 400 

 g 200 



1 — I — I — rn — i— 1 — I — n — i — i — i — i — i — r— i — i i i — r~\ — r 



\ CO2 Gradient 



Wind Speed 



(o) Predicted 



I I I I 



I I I I l_l I I 1_J I I I I L. 



8 10 12 14 16 18 20 22 24 26 28 30 

 July 



_l_l_l I I I L. 



2000 



1600 S 



E 



1200 .^' 

 <v 



800 "^ 



T3 



C 



'5 



400 



2 4 6 8 10 12 14 16 

 August 



FIGURE 4-9. Mean daily air, water, and sediment temperatures, mean 

 wind speed, and mean gradient of pCOi (water minus air) in Pond C, 

 1971. Circles are predicted data from regression analysis. (After Coyne 

 and Kelley 1974.) 



