Biogeochemistry of Nitrous Oxide Production in the Red Mangrove (Rhizophora mangle) Forest Sediments

This study was undertaken to quantify the emission and distribution of nitrous oxide and to explore its relation to pertinent physical and chemical parameters in a red mangrove forest located at Magueyes island, Puerto Rico. Rates of N2O evolution, which ranged from 0·05 to 1·4 mole m 2 h 1 (overall mean=0·50 mole m 2 h 1), are comparable to those of other previously studied ecosystems. A significant diel cycle of N2O emission was observed. Dissolved N2O concentration averaged 0·15 nmole cm 3 (SD=0·09, n=54) with a range of 0·1 to 0·57 nmole cm 3. Dissolved and exchangeable inorganic nitrogen was present mostly in the form of ammonium (overall mean=212·2 nmole cm 3) with lesser amounts of nitrate (overall mean=29·0 nmole cm 3). Redox potentials in the sediments generally decreased with depth, with a mean value of 377 mV at the sediment surfaces and lower mean value (159 mV) at 10 cm. We have explored the probable sources of N2O in the mangrove forest sediment using correlation analysis between the data obtained in this study and comparing these observations with previous studies of N2O metabolism. Our results, while not excluding the possibility of N2O production through denitrification, indicate that N2O is produced mainly by nitrification in sediments of this mangrove forest.