Increase of nitrous oxide flux to the atmosphere upon nitrogen addition to red mangroves sediments

Response of nitrous oxide N2O sediment/air flux to nitrogen addition was assessed in mangrove (Rhizophora mangle) sediments. Fluxes were enhanced with both ammonium and nitrate loading. Greatest fluxes (52 μmol m−2 h−1) were obtained with ammonium addition and saturation was achieved with additions of 0.9 mol m−2. Maximum flux following ammonium addition was 2785 times greater than control plots and 4.5 times greater during low tide than with equivalent ammonium addition at high tide. Nitrate enrichment resulted in exponential growth, with maximal mean flux of 36.7 μmol m−2 h−1 at 1.9 mol m−2; saturation was not achieved. Differential response to ammonium and nitrate, and to tide and elevation, indicate that microbial nitrification is responsible for most of the observed gas flux. Mangrove sediments constitute an important source of global atmospheric N2O and increases in nitrogen loading will lead to significant increases in the flux of this atmospherically active gas.