『Abstract
　The seasonal pattern and primary mechanism of nitrogen (N) export by surface runoff from the Wuchan subwatershed (WCW), an agricultural upper watershed (1.88 km²) located in southeast China, were investigated based on extensive streamwater measurements in 2004-2005 under subtropical climatic conditions. The results disclosed a highly variable but strong linkage between hydrological and anthropogenic controls and N export. n export via surface runoff presented a significant seasonal pattern caused by changes in rainfall and watershed N input. Approximately 75% of the annual N export (67 kg ha^-1) was flushed by those storm runoff mainly occurred during the wet season (march through September). The WCW dataset of N concentrations and loads during both baseflow and stormflow implied an interactive effects of anthropogenic N input and hydrology conditions: n export was flush-driven in late spring, summer and autumn 'wet season), but highly related with soil N in winter and early spring. Compared to undisturbed watersheds under similar rainfall conditions, WCW exported a considerable amount of n due to intensive fertilizer application ( a mean of 690 kg N ha^-1 year^-1, commonly as surface application). This work provides a first characterization of a small agricultural Chinese catchment under subtropical climates and its associated N export behavior.

Keywords: Nitrogen export; Surface runoff; Seasonal pattern; Non-point source pollution』

Introduction
Materials and methods
　Description of study area
　Field sampling and laboratory analysis
　Data analysis
Results
　N concentration and load during baseflow
　N concentration and load during stormflow
　N export during streamflow
Discussion
　Anthropogenic controls on n export
　Hydrological effect on stream N
　Seasonal pattern and the primary mechanism of N loss
　N export and retention
Acknowledgments
References