CARBON IN FRESHWATER SYSTEMS 259 



TABLE 9 



NET ECOSYSTEM ORGANIC-CARBON BUDGET, 

 LAWRENCE LAKE, MICH. 



productivity, and turnover is very high. Thus the NEP equation is an awkward 

 way to ascertain the status of the biota. Furthermore, much aquatic productivity 

 quickly enters the detritus pool, which represents the vast bulk of organic 

 carbon in water, i.e., dissolved organic carbon. The turnover of this storage pool 

 is also high, and unresolved estimates calculated by the NEP equation are 

 relatively meaningless. As discussed here and by Wetzel et al. (1972), a 

 detrital— dynamic structure exists in aquatic ecosystems which parallels the 

 trophic— dynamic structure (biota) originally described by Lindeman (1942). 

 Much of the detrital material in flux through this system is, indeed, respired to 

 C0 2 by various elements of the biota and falls into the respiratory categories 

 [Rs(A) + Rs(H)l of the NEP equation. The operation of at least two phenomena 

 associated with detrital— dynamic structure are recognized, however, for which 

 the term NEP may be legitimately and very usefully applied. 



Detritus as a Component of the Environment 



A detrital— dynamic equilibrium exists for both the dissolved and particulate 

 phase of detritus in natural waters at which rates of production and utilization 

 are equal. This concentration has its own impact upon the chemical and physical 

 milieu. Examples include the adsorption and coprecipitation of dissolved organic 

 matter and CaC0 3 in hard waters and the formation of organic aggregates. In the 

 Lawrence Lake case, a rather large amount of DOC is lost with the export of 

 water through an outlet stream. Although this is certainly organic export, it 

 actually represents another dimension of the dynamic situation within the lake 

 where production is closely tied to factors contributed from the watershed 

 (Wetzel, 1970), and export is similarly tied to the physical flow of water through 



