Chemistry 87 



an average of 29 ^g Cu liter"' (ionic plus some organic) for 136 lakes in 

 northeastern Wisconsin. The ponds appear to be closer to the average 

 seawater composition of 10 ^g Zn, 3 ^g Cu and 0.03 ^g Pb liter ' given by 

 Goldberg (1965). 



The copper and zinc concentrations in the pond sediments (Table 4-3) 

 fall within the range reported for the lakes mentioned above. 



CARBON DIOXIDE SYSTEM * 



Alkalinity and pH 



The pH and alkalinity of a number of ponds, subponds and of 

 Ikroavik Lake were measured weekly in 1970 and 1971 in order to 

 calculate the available carbon for photosynthesis studies. 



The alkalinity of the ponds was low and generally stabilized by 

 midsummer at 0.35 to 0.45 meq liter"' (Figure 4-7a). As expected, the 

 meltwater of the early weeks contained very low amounts of alkalinity; as 

 the pond became more concentrated and as the equilibria with the 

 sediments became established, the quantity rose. The next summer (Figure 

 4-7b) was wetter (see Chapter 3 ) and the alkalinity stabilized at a slightly 

 lower level (0.32 to 0.36 meq liter" '). 



The pH of the ponds followed the trends of the alkalinity (Figure 4- 

 7c) and was low early in the summer but then rose to a plateau by 1 July 

 and remained between 7.05 and 7.45 (mean of 7.18). The next summer the 

 pH plateaued between 7.24 and 7.62 (mean 7.37). 



Because the waters are poorly buffered, even the low rates of 

 respiration and photosynthesis in these ponds produce measurable changes 

 of pH and alkalinity during a single day. For example, in Pond C on 23 to 

 24 July, 1971, the alkalinity changed by 0.02 meq liter"' and the pH by 

 0.5. For this reason, it is important to take chemical samples at the same 

 time each day. 



Total Inorganic Carbon 



The measurement of the total inorganic carbon was a rapid way to 

 examine changes in CO 2 due to respiration and also to measure the 

 inorganic carbon available for photosynthesis. In 1971, this total was 

 measured weekly in four ponds and in Ikroavik Lake. It was measured 

 twice weekly in Pond B in 1972 and weekly in three other ponds. In 1973, 

 there were 40 measurements in Pond B and 16 in Pond C. 



*J. Keliey and P. Coyne 



