Role of Organic Nitrogen and Carbon in Canal Sediments on Drainage Water in Paddy Fields

抄録

In paddy fields, the drainage canal sediments can act as a pollutant source without proper management. The objective of this study is to evaluate the role of the sediments on the nitrogen (N) and organic carbon (C) concentrations in drainage water in paddy fields. Drainage canal sediments were sampled at three paddy-field districts around Lake Biwa and incubated for 28 days. Results of the experiments confirmed that the drainage canal sediments had enough potential as N and C sources. The sedimentary total N and C concentrations were 1.95 – 3.38 and 21.1 – 32.8 mg/kg, respectively. Nitrogen in the sediments existed mainly in the organic state. During the incubation experiment, large amounts of NH₄-N were released from the sediments. Fluorescence peaks of humic-like substance had strong correlation with dissolved organic N and C in the overlying water on the incubated sediments. It can be concluded that large amounts of organic N in the sediments can be a long-term NH₄-N source for the overlying drainage water through decomposition and release.