Chemistry 167 



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Moximum Wind Speed, (msec ) interval 



FIGURE 4-34. Sedimentation rates at various wind speeds. The 

 speeds are the maximum recorded speed over the sampling interval. 



precipitation of an iron-humic floe, and by resuspension of the sediment. 

 POC is lost from suspension by settling out when water currents are 

 minimal and by ingestion by zooplankton. 



One way to examine the resuspension is to measure the POC settling 

 out in the ponds. Because the concentration of the POC in suspension is 

 relatively constant, the amount settling to the bottom must equal the 

 amount resuspended. The problem becomes a methodological one, 

 however, as any sediment traps put into the pond inevitably affect the rate 

 of sedimentation. For example, small diameter traps suspended in lakes 

 are supercollectors (Miller 1972, Rich 1970) and collect much more POC 

 than actually sinks. This is especially true during circulation periods when 

 the traps collect a portion of the POC passing across the traps, not merely 

 the amount sinking down. 



One other problem is that in the ponds the suspended material 

 remains quite close to the bottom and can not be sampled by tall traps. For 

 example, white Plexiglas plates placed on the bottom collected much more 

 POC over 3 days than did 8-cm or 16-cm tall traps nearby (Figure 4-33). 



Our standard trap was a 4.7-cm-diameter cylinder 12 cm or 16 cm 

 tall, placed on the bottom. These collected from 0.46 to 28 g dry wt m '"^ 

 day '.In Pond D, the averages were 3.3 in 1971, 6.8 in 1972, and 4.4 g in 

 1973. As noted in Figure 4-33, this is an underestimate of the total 

 resuspension but is still a very large quantity of material. In fact, it is so 

 much greater than the total POC sampled in the water, that we suspect 

 that most of this material is resuspended during brief periods of high wind 

 and faster currents. A correlation study of the wind speed and the 



