『Abstract
　Temporal and spatial dynamics of nitrogen in lake and interstitial water were studied monthly in a large shallow, eutrophic lake in subtropical China from October 2002 to September 2003. The distribution of nitrogen was consistent with the idea that high nitrogen concentrations in the western part of the lake resulted from high levels of the nutrients from the surrounding cities through sewage-drainage systems. Nitrate was the predominant form of nitrogen in the overlying water, while ammonium was predominant in the interstitial water, indicating that strong oxidative nutrient regeneration occurred near the sediment-water interface. Nitrate could be an important dissolved inorganic matter source for phytoplankton, which in turn influenced the seasonal variations of nitrate concentrations in lake water. significant positive correlation between ammonium fluxes and water temperature was observed and could probably be attributed to the intensified ammonification and nitrate reduction with increased temperature. Positive correlation between ammonium fluxes and algae biomass and Chl a concentrations may indicate that phytoplankton was an important factor driving ammonium fluxes in our study lake, and vice versa that higher fluxes of ammonium supported a higher biomass of the phytoplankton.

keywords: Nitrogen; Eutrophic; Flux; Sediment-water interface; Lake Chaohu』

Introduction
Materials and methods
　Description of study lake
　Sampling and assay
　Diffusive flux calculation
Results
　Sediment characteristics
　Lake and interstitial water
　Diffusive ammonium fluxes
Discussion
　Vertical and spatial variations of nitrogen
　Seasonal variation of nitrogen and correlation with phytoplankton
　Diffusive ammonium fluxes
Acknowledgments
References