Figure l.--Mayaguana (Abrahams Bay) Coral Reef and Lagoon, 



x indicates the study area. 



Depths in fathoms 



in 



MATERIALS AND METHODS 



This study was conducted during May 1983 in Abrahams Bay, Mayaguana, located 

 the southern Bahamas (fig. 1). 



Dead coral heads, each with a displacement volume of about 250-300 cm^, 

 were collected by SCUBA divers from several areas behind the reef crest. The 

 heads which were covered with algae and organic matter were brought back to the 

 ship's laboratory and placed in gas tight glass incubation chambers (Seitzinger, 

 et a_L_, 1980) which were then filled to within 1 cm of the top with reef water 

 "[500 ml). Denitrification rates were measured using acetylene to inhibit N2O 

 reduction to N2 (Balderston, et al_^, 1976). The gas phase (60 ml) was flushed 

 with acetylene, and the water in the chambers was stirred with floating magnetic 

 stir bars to equilibrate the gas and water phases. Samples (30 ml) of seawater 

 were then withdrawn at time intervals into stoppered 50 ml serum bottles and 1 

 ml of saturated K0H solution added to each. After 3 hr a concentrated NO3 solution 

 was added to two of the chambers to make the seawater concentration 40 uM NO3. 

 Time-series samples for N2O continued to be taken at 7, 9, and 17 hr. The N2O 

 concentration in the gas phase of the serum bottles was measured by ECD gas 

 chromatography within 1 week (Seitzinger, et al . , 1980). The total amount of 

 N2O in the samples was calculated using Weiss and Price's (1980) N2O solubility 

 equation for the appropriate temperature and salinity. The production of N2O 

 in the presence of acetylene by the coral heads then was calculated based on 

 the change in concentration between sequential samples and equated to the 

 denitrification rate. 



The potential for denitrification in the sediments from the reef lagoon was 

 examined using measurements of pore water NO2 and NO3 concentrations, NO3 

 reduction rate measurements, and measurements of N2O production in the presence 

 and absence of acetylene. Sediment cores (47 cm 2 x 25 cm deep) were collected 



200 



