Dissolved N 2 O concentrations in oil palm plantation drainage in a peat swamp of Malaysia.

Oil palm plantations in Southeast Asia are the largest supplier of palm oil products and have been rapidly expanding in the last three decades even in peat-swamp areas. Oil palm plantations on peat ecosystems have a unique water management system that lowers the water table and, thus, may yield indirect NO emissions from the peat drainage system. We conducted two seasons of spatial monitoring for the dissolved NO concentrations in the drainage and adjacent rivers of palm oil plantations on peat swamps in Sarawak, Malaysia, to evaluate the magnitude of indirect NO emissions from this ecosystem. In both the dry and wet seasons, the mean and median dissolved NO concentrations exhibited over-saturation in the drainage water, i.e., the oil palm plantation drainage may be a source of NO to the atmosphere. In the wet season, the spatial distribution of dissolved NO showed bimodal peaks in both the unsaturated and over-saturated concentrations. The bulk δN of dissolved NO was higher than the source of inorganic N in the oil palm plantation (i.e., N fertilizer and soil organic nitrogen) during both seasons. An isotopocule analysis of the dissolved NO suggested that denitrification was a major source of NO, followed by NO reduction processes that occurred in the drainage water. The δN and site preference mapping analysis in dissolved NO revealed that a significant proportion of the NO produced in peat and drainage is reduced to N before being released into the atmosphere.