Preliminary studies on nitrous oxide emissions from the ornithogenic soils on Xi-sha atoll, South China Sea

摘要

The preliminary measurements of nitrous oxide fluxes from the ornithogenic soils on tropical Xi-sha atoll were made using a closed chamber technique for the first time. N_2O fluxes from the ornithogenic soils ranged from 1.8 to 40.3 mu g/(m~2 -h) on Dong Island and 3.2 to 20.4 mu g/(m~2-h) on Yongxing Island and their flux averaged 11.0 mu g/(m~2 centre dot h) and 8.3 mu g/(m~2 centre dot h), respectively. N_2O fluxes from two wetland sites in salt marsh of Dong Island were approximately one order of magnitude lower than those from the ornithogenic soils and averaged 2.1 mu g/(m~2 centre dot h) and 2,4 mu g/(m~2 centre dot h). The diurnal variation cycle in the fluxes was obtained at the observation sites; the N_2O flux increased with the increase in soil temperature. The sudden increase in soil moisture greatly stimulated N_2O emission from the ornithogenic soils on Dong Island due to the heavy rainfall. The undisturbed soils showed the lower N_2O fluxes and the average was 4.8 mu g/(m~2 centre dot h) and the soils via the reclamation showed the higher N2O fluxes and the average was 16.6 mu g/(m~2 centre h) on Yongxing Island, suggesting that the changes of land use have an important effect on N_2O fluxes from the ornithogenic soils. In addition, the N_2O fluxes at the different sites showed high spatial variations. The fluxes were positively correlated with the concentrations of NO_3~-. PO~(3-)_4 and Mn in the soils. The negative correlation between the fluxes and total S concentration in the ornithogenic soils was also found for the first time. Coastal soils or sediments constitute an important source of global atmospheric N_2O and the increases in nitrogen loading from seabird guanos will lead to significant increases in the flux of this atmospherically active gas.