inorganic nutrient fluxes are highly variable 



i 



CM 



CM 

 O 



l/> 



0) 



o 



E 

 E 



| RESPIRATION 

 f~1 GROSS PRODUCTION 



Figure 

 and gro 



3-5 5-8 8-14 14-20 

 DEPTH (m) 



1. Histogram of pooled oxygen data 

 ss production at increasing depths. 



20-30 



>30 



24 hour respiration 



DISCUSSION 



Depth dependence of community metabolism. 



The evident balance between gross production and respiration 

 throughout the depth range of Enewetak lagoon (Fig. 1) is misleading, 

 as will be discussed subsequently. However, the figure clearly ill- 

 ustrates that both parameters are depth dependent. Based on the 

 pooled data, gross production, regressed exponentially against depth, 

 yields a decay coefficient of 0.031 m~ * , with a correlation coeff- 

 icient (r 2 ) of 0.971. Similarly, the respiration decay coefficient 

 is also 0.031 m~ 1 , with r 2 equal to 0.985. The close adherence to an 

 exponential model establishes the correlation of sediment community 

 metabolism with incident light. Unfortunately, the lagoon extinction 

 coefficient has not been determined, but in the open ocean immediately 

 east of Enewetak, the extinction coefficient is 0.045 m~ ' (Colin, et 

 al., in prep.). Since the lagoon water column contains more partic- 

 ulate material than does the open ocean, the lagoon extinction coeff- 

 icient cannot be lower than 0.045 m~ l . Thus, although production and 

 respiration of lagoon floor communities are clearly light-driven, 

 benthic community activity is increasingly efficient at greater 

 depths. 



Lagoon floor heterotrophy . 



Assuming that the empirically determined values for RQ and PQ are 

 uniform throughout the lagoon floor, production and respiration can be 

 expressed as carbon equivalents. If measured oxygen fluxes are con- 

 verted to carbon equivalents by use of RQ and PQ values, it turns out 

 that more carbon is respired by the system than is produced, and the 



147 



