154 R. T. Prentki et al. 



When older leaves were placed in plastic bags and allowed to 

 decompose, it was found that 15 to 20% of the plant carbon remained as 

 DOC; we believe this DOC is resistant to bacterial breakdown 

 (refractory). This was shown in experiments with yellow Carex leaves 

 placed into plastic bags (Whirlpak) along with distilled water and 

 incubated next to the litterbags. The loss of dry weight from the Carex in 

 the plastic bags was very close to losses from the litterbags. This loss 

 equalled the DOC that accumulated in the plastic bags (controls of plastic 

 bags plus distilled water had no increase in DOC). After one summer of 

 incubation in plastic bags, the yellow Carex lost 25% of its dry weight and 

 19% of that dry weight was found as refractory DOC. Over the same 

 period, brown Carex lost only 16% of its initial dry weight while 15% 

 remained in the plastic bags as DOC. 



There is also evidence that most of the loss from the overwintering 

 leaves occurs in the first 2 weeks after the thaw. It is likely that in the older 

 leaves this rapid loss is caused by mechanical rupture during the freeze- 

 thaw process. In the green leaves, the initial loss is likely from the easily 

 soluble material. 



From the plastic bag and litterbag experiments and from production 

 estimates for the emergent plants, we estimate that there is a total input to 

 the pond of 3.9 g C m^^ of refractory DOC from sediments and 

 macrophytes and 5.6 g C m "^ of labile DOC from the grasses and sedges 

 (Table 4-23). This was calculated from the Carex annual production [80 g 

 C m " ^ (see Chapter 5) ] , the size of the Carex bed (40% of total pond), and 

 the loss rate from the bag experiments. Thus, the refractory DOC added to 

 the ponds from yellow Carex is 1.8 g C m^ and that from brown Carex is 



TABLE 4-23 Summary of the Sources of Dissolved Organic Carbon in Pond 

 Bin 1971* 



'Depth of the pond was taken as 20 cm. 



