Chemistry 89 



volume of water is injected into a weak acid solution and the evolved CO2 

 is measured with an infra-red gas analyzer (I RGA). 



The two methods of measurement gave very similar values for the 

 ponds (Table 4-5). Based on a group comparison "t" test, however, the 

 values were significantly different in two out of five ponds. This was likely 

 caused by the inclusion of organic acids in the titration value (Salonen and 

 Kotimaa 1975). 



The total inorganic carbon, as measured by the I RGA method, 

 ranged from 1.43 to 8.08 mg C liter ^ in Pond B with averages of 4.10, 

 5.01, and 2.73 in 1971, 1972, and 1973, respectively (Figure 4-8). In 

 general, the amounts were lowest after the spring melt, reached 

 equilibrium values about 1 July, and then changed slightly (usually an 

 increase) in August due to concentration of the ions as the pond volume 

 decreased. 



As mentioned above, there were daily changes in pH and alkalinity 

 and these are reflected in similar changes in the total inorganic carbon. 

 During the 23 to 24 July measurements, the change by the I RGA method 

 was 0.63 mg C liter ' and the change by the calculation method was 0.86. 

 Both methods showed the lowest concentrations during the late afternoon 

 and early evening and the highest concentrations during the night and 

 early morning. 



The concentration of inorganic carbon in these ponds is quite low. For 

 example, the values for inorganic carbon in both north German soft water 

 lakes (Hutchinson 1957) and for the average river water (Livingstone 

 1963b) are 3 times the Pond B average while the seawater has about 7 

 times this amount (Stumm and Morgan 1970). Lawrence Lake (Wetzel 

 1975), an alkaline marl lake, contains 10 times this amount or around 40 

 mg C liter \ while Mirror Lake in New Hampshire has around 1 mg C 

 liter "^ (Jordan and Likens 1975). 



TABLE 4-5 Mean and Standard Deviation of Total Inorganic Carbon 

 in 1971 as Determined by Two Methods* 



Pond Infrared gas Calculated from Group comparison 't' test 



analyzer pH and alkalinity observed (df) critical 5% level 



*Data are expressed as mg C liter' 



