[M-IS13] Biogeochemistry

[MIS13-12] Nitrous oxide emission from the drainage and the production processes in oil palm plantation on peatland

*Kazuya Nishina¹, Lulie Melling², Ryuichi Hirata¹, Yoshiyuki Takahashi¹, Sakae Toyoda³, Kotaro Terajima³, Masayuki Itoh⁴ (1.NIES National Institute of Environmental Studies, 2.SARAWAK Tropical Peat Research Institute, 3.Tokyo Institute of Technology, 4.University of Hyogo)

Keywords:Nitrous oxide, Oil palm plantation, Nitrogen stable isotope

In South-East Asia, oil palm plantation has rapidly expanded in the past few decades even in peatland areas. In the light of nitrogen cycling, this land-use change would result in enrichment on the ecosystem N cycling due to the N fertilization for the maintaining oil palm growth and the wastewater emission from the palm mills in the plantation. Oil palm plantations converted from peat swamp forests require the drainage to keep cultivation and thus has unique hydrological characteristics. In such plantation, drainage water surface dominates up to 5% of plantation area and therefore it is important to evaluate the gas exchange between the drainage water and atmosphere.

In this study, we have conducted spatial sampling for dissolved N₂O concentration (dN₂O) in the oil palm plantation on drained peat soil in July 2018, in Sarawak, Malaysia in order to evaluate the indirect N₂O emission from palm oil plantation. We have intensively sampled the water samples from the drainage in the plantation (ca. 120 km²) and the water samples from Raja river, which is adjacent to the plantation. 90% of samples (N = 84) in the drainage water showed over-saturation in dissolved N₂O concentration (up to 570%), suggesting that the drainage water in the oil palm plantation acts the source of N₂O to the atmosphere. The emission factor for indirect emission (EFr: i.e., dN₂O/nitrate concentration) showed relatively higher than the default EFr in IPCC. However, there were no clear linear relationships between the water qualities (including nitrate) and dN₂O. We have also analyzed the isotopic composition of dN₂O in both drainage and river samples. This analysis suggested the denitrification contributed dN₂O in the drainage water.