NO3^ - concentrations sampled monthly in the Wuchuan stream, which is a small agricultural headwater stream in the southeast of China, within two years, were used to study the stream＇s nitrogen saturation characteristics. Results showed that NO3^ - concentrations varied from 35.5 to 319. 5μeqL^-1 in 2005 and from 5.0 to 353.6 μeqL^-1 in 2007. And, according to the criteria proposed by Stoddard and Traaen, the nitrogen saturation status of the stream was at stage 2 or 3, and stage 2, respectively. Both stages were closed to saturation. It was found that the saturation stage would increase with the NO3^- concentration, which caused the change of nitrogen saturation stage in the Wuchuan stream over time. The increasing of nitrogen loadings has led to the stream nitrogen saturation and eventually can alter nitrification, denitrification and other nitrogen biogeochemical cycles in the stream ecosystem.%以九龙江流域典型的农业源头溪流——五川溪为研究区域，开展每月一次共2年的NO，一采样用于溪流氮饱和特征的研究．结果表明，2005年和2007年溪流的NO，一浓度分别为35．5～319．5μeqL^-1和5．0～353．6μxeqL^-1，根据Stoddard和Traaen提出的氮饱和划分准则，五川流域分别处于氮饱和阶段2／3和阶段2，接近氮饱和．氮饱和阶段随着NO。一浓度的增加而上升，五川溪流的氮饱和阶段存在着时间上的变化．河流生态系统中氮负荷增加，使河流达到氮饱和状态，并最终改变溪流系统硝化和反硝化等氮的生物地球化学循环过程．随着NO，一浓度的增加，五川源头溪流已成为流域内重要的NO3^-源．
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