252 



WETZEL AND RICH 



Submersed macrophytes 

 and attached algae 



Emergent macrophytes 

 and eulittoral algae 



INCREASING FERTILITY 

 Fig. 3 Generalized relative contributions of phytoplankton, chemosynthetic 

 dark C0 2 fixation, and allochthonous sources of dissolved organic carbon 

 (DOC) to lakes of increasing fertility in the progression of dominating pelagic 

 and littoral flora (see Fig. 2). 



TABLE 4 



CHEMOSYNTHETIC RATES OF DARK C0 2 FIXATION IN THE 

 PELAGIC ZONE OF LAWRENCE LAKE, MICH. 



through the DOC pool annually. This percentage likely decreases as systems 

 become more eutrophic, particularly where littoral metabolism becomes 

 dominant. 



POC suspended in the water column of Lawrence Lake followed a 

 conspicuously consistent pattern both seasonally (see Wetzel, Rich, Miller, and 

 Allen, 1972) and from year to year (Table 5). Fluctuations in the POC pool 

 closely paralleled those of phytoplankton primary productivity. A gradual 



