Temporal and spatial patterns of N2O and CH4 emissions on an agricultural field containing ephemeral wetlands.

It has been recognized that both N 2O and CH 4 emissions vary with land use and slope positions. In various parts of the world, wetlands are imbedded in the agricultural landscapes. However, to date, no study has been carried out to examine the N 2O and CH 4 emissions from agricultural fields containing ephemeral wetlands. In this study, gas samples were collected for four consecutive years (2003 to 2006) from different slope positions along three transects from a No.Till cropped upslope through the riparian area to the wetland. Additionally, gas samples were taken from three adjacent cropped depressions for a two.year period. Although the daily fluxes of N 2O and CH 4 emissions were highly variable, there were distinctive temporal and spatial patterns. These patterns reflect the effects of the hydrological regime and land management practice which are related to the land use and slope positions. Overall, on an annual basis, the total non.CO 2 GHG emission rates from the wetland basin were much greater than those from the cropped area. The riparian zone served as a transition zone with the highest variability of N 2O and CH 4 emissions. These findings suggest that the N 2O and CH 4 emissions from ephemeral wetlands imbedded in the agricultural landscapes must be taken into account.