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

BIOGEOCHEMISTRY OF NITROUS OXIDE PRODUCTION IN THE RED MANGROVE (Rhizophora mangle) FOREST SEDIMENTS

Jorge Bauza, Julio M. Morell and Jorge E. Corredor
Department of Marine Sciences
University of Puerto Rico
Mayaguez, Puerto Rico 00680

RUNNING HEAD: Nitrous Oxide in Mangrove Sediments

keywords: nitrous oxide, nitrification, mangrove forest

ABSTRACT The present study was undertaken to quantify the emission and distribution of nitrous oxide and to explore its relation with pertinent physical and chemical parameters of the red mangrove forest sediment. Rates of N2O evolution, which ranged from 0.052 to 1.37 ƒÝmole.m-2.h-1 (overall mean = 0.495 ƒÝmole.m-2.h-1), are comparable to those of other ecosystems that has been previously studied. A significant diel flux change in nitrous oxide emission was observed. Dissolved nitrous oxide concentration averaged 0.149 nmole.cm-3 (SD = 0.09, n = 54) with a range from 0.096 to 0.574 nmole.cm-3. Dissolved and exchangeable inorganic nitrogen was present mostly in the form of ammonium (from 199 to 272 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 deep. We have explored the probable sources of nitrous oxide in the mangrove forest sediment using linear and multiple regression and correlation between the data obtained in this study and comparing this 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.

INTRODUCTION

Nitrous oxide is a trace gas produced under natural conditions by the processes of nitrification and denitrification as part of the biogeochemical cycle of nitrogen (Firestone and Davidson, 1989). It was not until

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