346 J. E. Hobbie et al. 



ethylamine-saturated filter paper, and the subsample filtered through a 

 membrane filter. Both filter paper and membrane filters were counted with 

 liquid scintillation. The curve of uptake plotted against the substrate 

 concentration resembles an enzyme saturation curve and is analyzed 

 according to MichaeUs-Menten kinetics. If the substrate concentration, 

 S„, could be measured, then a velocity of uptake could be determined and 

 would be the best activity measurement. However, Sn is only a few parts 

 per billion and is difficult to measure. Instead, the useful parameters are 

 the maximum uptake velocity (Vmax), turnover time (T,), and the half- 

 saturation constant plus substrate concentration {K, + Sr,). 



Kinetic parameters were determined in Pond B in 1971 using '"C- 

 labeled glucose, proline, and aspartic apid (Table 8-4). The V^a. and 

 turnover times calculated for glucose in these experiments indicate a 

 moderately high bacterial activity in the plankton and a relatively low 

 bacterial activity in the sediments compared with other studies (Table 8-5). 



Diurnal variation of K„„, may be significant; it ranged from 0.122 to 

 0.761 Mg C liter "^ hr ' in an experiment conducted on 19 to 20 August 

 1972 in Pond B (Figure 8-3a). This was hkely due to temperature alone as 

 regression of temperature vs. V„ax for this experiment shows a correlation 

 coefficient of 0.71 (10 J/)(Figure 8-3b). 



In ponds B and C the Vmax for uptake of acetate in the water column 

 correlated positively (r = 0.62), at the 0.05 level of significance, with 

 primary productivity (Figure 8-4). These data exclude the period of spring 

 runoff when much of the DOC in the ponds likely comes from outside the 



TABLE 8-4 Kinetic Parameters for the Uptake of Organic Compounds from 

 Water of Pond B, 1971 



* J^max in fJg liter ' hr ' 

 t (A: + 5)in)UgUter"^ 

 **7'in hours 



