Abstract: 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
μg/(m^2·h) on Dong lsland and 3.2 to 20.4
μg/(m^2·h) on Yongxing lsland and their flux
averaged 11.0 μg/(m^2·h) and 8.3 μg
(m^2·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 μg/(m^2·h) and 2.4
μg/(m^2·h). The diurnal variation cycle in the
fluxes ws 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 lsland due to the heavy rainfall. The undisturbed
soils showed the lower N_2O fluxes and the average was 4.8
μg/(m^2·h) and the soils via the reclamation
showed the higher N_2O fluxes and the average was 16.6
μg/(m^2·h) on Yongxing lsland, 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.
Keywords: South China Sea, ornithogenic soil, nitrous oxide, Xi-sha atoll, emission