Nitrous oxide fluxes in red mangroves sediments on the south west coast of Puerto Rico (Rhizophora mangle)

Measurements of nitrous oxide concentrations in air and sediment/air fluxes were performed in different mangrove (Rhizophora mangle) sediments on the southwest coast of Puerto Rico. N₂O was quantified by gas chromatography using a 63Ni electron capture detector and incubation chamber techniques. Baseline N₂O concentrations averaged 314 ppb with a range from 267 ppb to 353 ppb. Fluxes ranged from −860.7 to 818.8 nmole.m−2 h−1 with an overall mean of 125 nmole.m−2 h−1. Ninety-one percent of the measurements exhibited net N₂O flux to the atmosphere while the balance exhibited consumption by the sediments. N₂O production was higher (23%) at low tide when sediments are exposed to air, indicating that nitrification is the probable mechanism of N₂O production. Ammonium was the most abundant dissolved inorganic nitrogenous species with concentration, ranging from 23 μM to 342.7 μM. N₂O fluxes were enhanced in response to ammonium and nitrate loading. The highest fluxes were obtained with NH₄+ addition to the sediments reaching saturation near 0.9 mol.m−2, with a mean N ₂O flux of 52 μmole.m−2 h−1. The NO₃− curve exhibits an exponential growth with a maximum mean flux of 36.7 μmol.m−2 h −1. We conclude that nitrifying bacteria are the main precursors of N₂O in red mangrove sediments.