94 R. T. Prentki et al. 



TABLE 4-7 Third Order Partial Correlation Coefficient Matrix for Pond C 

 and North Meadow Lake 



Temp (°C) 



POND 

 Air temp. 

 Water temp. 

 Sediment temp. 

 Wind speed 

 CO 2 gradient 



LAKE 

 Air temp. 

 Water temp. 

 Sediment temp. 

 Wind speed 

 CO 2 gradient 



Source: Coyne and Kelley 1974 



*Significant (0.05 probability level) 



t Highly significant (0.01 probability level) 



the lower CO 2 gradient in the lake reflects its greater depth than the ponds 

 (70 vs. 40 cm). Mainly, however, it reflects the lower rate of respiration in 

 the lake than in the ponds. We attribute this to the small amount of 

 organic matter per square meter that enters the lake from the rooted 

 aquatics along the shore. The ponds, in contrast, have a smaller area and 

 so the rooted plants contribute a significant amount of organic matter per 

 square meter. 



There was a short period of undersaturation of CO2 in the lake (10-13 

 July, Figure 4-10). There is no obvious physical cause of this 

 undersaturation so it could have been an algal bloom in the water or 

 sediments. Unfortunately, no additional measurements were taken. 



The factors that affect the PCO2 are respiration, water temperature, 

 and wind speed. Respiration should increase with increasing temperatures 

 (a Qio of around 2) and thus increase the size of the CO2 gradient. An 

 increase in temperature when the water is already supersaturated with 

 CO 2 would increase the tendency of the CO 2 to leave the water and 

 therefore would appear as a high CO 2 partial pressure in the water. The 

 rate of turbulent exchange across the water surface should increase with 

 wind speed and thereby decrease the CO 2 gradient. 



From the data on the pond and on the lake, separate multiple 

 regression equations were calculated (Table 4-7). The third-order partial 

 correlation coefficients show a direct relationship between sediment 

 temperature and CO 2 gradient but indirect relationships between water 

 temperature, wind speed, and CO 2 gradient. The regression explained only 



