168 



R. T. Prentki et al. 



200 400 600 800 



Mean Annual POC. /ig C liter"' 



FIGURE 4-35. Mean annual concentration of POC 

 vs. the mean annual sedimentation rate for six ponds. 



sedimentation showed a direct relationship (r = 0.66, HS) with the 

 maximum wind speed (Figure 4-34) and no correlation with the average 

 wind speed. 



Ponds with the highest sedimentation rate had the lowest average 

 POC in the water and vice versa (Figure 4-35). The mean annual 

 sedimentation rate is inversely related to the mean annual POC 

 concentration with r= —0.93 (n = 6, HS). One explanation is that the large 

 particles that fall to the bottom (average diameter of 200 ^lm) actually 

 clear the water as they fall. This could be an adhesion of the small particles 

 to the large ones or a co-precipitation. This co-precipitation was also 

 found in an arctic lake (Hobbie 1973) but inorganic silt, rather than 

 organic matter, was involved. 



Zooplankton Grazing 



The grazing of the zooplankton might be another control on the POC 

 in these ponds. As will be discussed (Chapter 6), the zooplankton are 

 capable of filtering all the water in a pond every few days. If these animals 

 are affecting the POC concentration, then the highest zooplankton 

 populations should be found in ponds with the lowest POC concentrations. 

 This is actually the case (see Chapter 6) and there is a highly significant 

 inverse correlation between POC concentration and maximum 

 zooplankton biomass (r= —0.95, n = 8). This same relationship can also be 

 used to argue that the zooplankton had a higher production when lower 



