『Abstract
　The nitrogen (N) budget calculation approach is a useful means of evaluating the impact of human activity on the N cycle. Field scale N budget calculations may ignore the interactions between landscapes, and regional scale calculations rely on statistical data and indirect parameters. Watershed scale budget calculations allow for a more direct quantification of n inputs and outputs. We conducted N budget calculations for a rice paddy-dominated agricultural watershed in eastern China for 2007-2009, based on intensive monitoring of stream N dynamics, atmospheric deposition, ammonia (NH3) volatilization and household interviews about N-related agricultural activities. The results showed that although total N input to the watershed was up to 280 kg N ha^-1 year^-1, riverine discharge was only 4.2 kg N ha^-1 year^-1, accounting for 1.5% of the total n input, and was further reduced to 2.0 kg N ha^-1 year^-1 after reservoir storage and/or denitrification removal. The low riverine N output was because of the characteristics of the rice paddy-dominated landscape, which intercepts run-off and enhances soil denitrification. The watershed actually purified the N in rainwater, as N concentrations in river discharge were much lower than those in rain water. Major N outputs included food/fed export, NH3 volatilization from chemical fertilizer and manure, and emissions from crop residue burning. net reactive gaseous emissions (emissions minus deposition) accounted for 5.5% of the total N input, much higher than riverine discharge. Therefore, the agricultural n cycle in such paddy-dominated watersheds impacts the environment mainly through gas exchange rather than water discharge.

Keywords: Eastern China; nitrogen budget; Reservoir; Riverine discharge; Watershed』

Abbreviations
Introduction
Materials and methods
　Watershed description
　Nitrogen budget model
　Household interviews of N related agricultural activities
　Atmospheric N deposition
　Chemical N fertilizer input and biological N fixation
　NH3 volatilization from chemical N fertilizer and human/livestock excreta
　Dissolved N concentrations and N discharge into and out of the reservoirs
　Sediment storage and denitrification
　Nitrogen output through food/feed export and crop residue burning
　Uncertainty analysis
Results
　Hydrology
　Nitrogen concentrations in stream water and reservoir discharge
　N storage and/or removal in reservoir, streams and ponds
　Nitrogen budget and uncertainties
Discussion
　Potential causes of low riverine n export
　Environmental implications of N export from rice paddy-dominated agricultural watersheds
　Fate of surplus N
Conclusions
acknowledgments
References