『Abstract
　Although nitrous oxide emission from agricultural leaching and runoff is thought to constitute a globally important source of this greenhouse gas, water dissolved N2O in paddy ecosystem is poorly understood and scarcely reported where large amounts of fertilizer nitrogen are applied. This paper gives the results of a study assessing variability of the relationships between N2O and NO3^- concentration in leachates from packed soil mesocosms, monolith lysimeters, and in wells, rivers, and lakes in a region of China where land use is dominated by rice agriculture. Mesocosm and monolith experiments involved different application rates and types of fertilizer. From repetitive observations for each treatment in laboratory and field experiments and the results of the field surveys, we found that the average N2O/NO3^- ratios in groundwater varied across space and were much lower than the current IPCC default value. Riparian zones may be hotspots of N2O production in the Taihu Valley and significant loss of NO3^- occurs in riparian and surface water habitats. These findings are useful for calculating N2O emissions from aquatic ecosystems and lowland paddy agroecosystems.

Keywords: Dissolved nitrous oxide; Greenhouse gases; Groundwater; Nitrate leaching; Paddy field; Surface water』

1. Introduction
2. Materials and methods
　2.1. Soil mesocosms with year-round flooded-drainage irrigation regime
　2.2. Monolith lysimeter experiment with lowland rice-winter barley annual rotations
　2.3. Measurements in aquatic system of Taihu Valley: multi-site and year-round observations of dissolved N2O and NO3^- in well, lake and river water
　2.4. Measurement of N2O dissolved in water and analysis of NO3^- and NH4⁺
　2.5. Data analysis
3. Results and discussion
　3.1. Lower EF5-g with large spatial variations in the leachates and groundwater
　3.2. Large difference in EF5-r between the surface lake and river waters indicating hotspots of N2O production in Taihu riparian zone
4. Conclusions
Acknowledgements
References