Concentration, jjM 



Figure 2. --Depth profile of pore water nitrite (circles) and NO2 + NO3 (triangles) 



in sediments of lagoon. 



the absence o_f acetylene was measured in a parallel set of_samples incubated 

 with 20 U M NO3 but without acetylene. The reduction of NO3 also was_measu£ed 

 in another parallel set of samples with acetylene and 20 yM NO3. NO2 + NO3 

 concentrations were measured immediately after approximately 0, 6, and 15.5 hr 

 (KOH was not added). 



RESULTS 



When coral heads were incubated in seawater that was not enriched with 

 nitrate, the rate of denitri fication (N2O production in the presence of acetylene) 

 was approximately 1-2 nmol N2O per coral head per hour (table 1). When the NO3 

 concentration in the surrounding seawater was increased to 40 pM, the rate of 

 N2O production increased to approximately 50 nmol per hour per coral head and 

 then decreased during the subsequent 14 hr. 



202 



