166 



R.T. Prentkietal. 



find a correlation between POC concentration and the average daily or 

 maximum wind speed were equally unsuccessful. Certainly there are daily 

 changes (e.g., 1 3 August 1973, Table 4-28) in the POC and similar changes 

 have been noted for the bacteria throughout a single day (see Chapter 8). 

 The causes of these changes — wind, water currents, and micro- 

 turbulence — are difficult to measure. 



In spite of the extreme shallowness of the ponds and the 

 accompanying close contact with the sediments, the POC concentrations 

 are very similar to those found in the epilimnion of moderately productive 

 lakes. For example. Lake Erken in Sweden (Hobbie 1971) had a 

 concentration that was usually between 500 and 800 Mg C liter"' (a peak 

 of 1500 during an algal bloom) and Lawrence Lake in Michigan had 

 concentrations of 200 to 800 ^g C liter ' ' in the circulating water (Wetzel 

 et al. 1972). In Lake Tahoe, an extremely oligotrophic lake, POC ranged 

 from 19 to 38 Mg C liter " ' while coastal ocean waters had 30 to 300, open 

 ocean waters 5 to 50, and Arctic Ocean water 1 to 7 Mg C liter ^^ (Holm- 

 Hansen 1972). Algal biomass was estimated to be 10% of the total POC 

 (Hobbie 1971) in Lake Erken while Miller (1972) calculated that 7% of the 

 POC was made up by living organisms in Lawrence Lake. 



Sedimentation of POC 



The POC in the ponds is produced by the growth of algae and 

 bacteria, by their death, by defecation and molting of the zooplankton, by 



1.0- 



o 



■a 





T3 



0.1 



0) 



o 

 Q. 



□ 



a. 



1.0— * 



a. 

 o 



E 

 o 



00 



O)^ 



South Shore 



North Shore 



FIGURE 4-33. Rate of POC sedimen- 

 tation onto a flat plate and into sedi- 

 ment traps 8 cm and 16 cm high; Pond 

 C, 3 to 5 August 1973. 



