Table l.--Rate of denitrification by dead coral heads as measured by N2O 

 production (nmol NoO_h coral head -1 ) in the presence of acetylene, 

 but without added NO3, except as indicated. Acetylene was added at 

 time = hr. * = afte£ 3 hr a concentrated NO3 solution was added to 

 make seawater 40 pM NO3. 



Dead Coral Head 



Incubation Period 



Rate of N2O Production 

 nmol N 2 h" 1 



1 

 2 

 3 



2.5 - 5.5 hr 



2 - 5 hr 



- 3 hr 



*3 - 7 hr 



7 - 9 hr 



9 - 17 hr 



- 3 hr 



*3 - 7 hr 



7 - 9 hr 



9 - 17 hr 



1.3 



2.1 

 1.6 



57 

 38 

 16 



0.8 

 51 

 16 



6 



by SCUBA divers from the Thalassia beds in the reef_lagoon._ One core was 

 sectioned at 2.5 cm intervals and the pore water NO2 and NO3 concentrations 

 determined using a Technicon AutoAnalyzer. 



NO3 reduction rates were measured in a second core sectioned at intervals 

 of 0-5 cm, 10-15 cm, and 20-25 cm. Sediment slurries from these depths were 

 placed in serum bottles with 20 y M NO3 seawater solution and the change in NO2 

 + NO3 concentration with time measured. The incubations were done in the dark 

 at 29°C. 



Denitrification rates in the lagoon sediments were measured, again using 

 acetylene inhibition of N 2 reduction. Sediments from three cores were sectioned 

 at intervals of 0-5 cm, 10-15 cm, and 20-25 cm. Sediment slurries (14 cm 3 ) 

 from those depths were incubated aerobically in serum bottles with 15 ml of 20 

 uM NO3 seawater solution and 0.3 atmospheres of acetylene. N2O production 

 rates in the presence of acetylene then were measured at each depth after 

 intervals up to 15.5 hr by injecting 2 ml of a saturated K0H solution into the 

 serum bottles after approximately 0, 6, and 15.5 hr. The production of N2O in 



201 



