[Dynamic characteristics of nitrogen and phosphorus in the representative input tributaries of Danjiangkou Reservoir]

Three representative input tributaries of Danjiangkou Reservoir in the upper reach of Hanjiang River, the largest tributary of Yangtze River, were selected for annual water quality monitoring from April 2010 to April 2011, to analyze dynamic characteristics of nitrogen (N) and phosphorus (P) in the river mouth areas, and then to assess the states of nutrition by comprehensive trophic level index. The results showed that the annual average concentrations of total nitrogen (TN) and total phosphorus (TP) in Shendinghe River, receiving both industrial and domestic wastewater from Shiyan City, were 11.63 mg x L(-1) and 0.93 mg x L(-1), which were 3 times and 12 times higher respectively comparing to that of Wulongchi stream that received little agricultural non-point source pollution. While for Dabaihe River, polluted by moderate agricultural non-point source pollution combining with waster water from a small town, had slightly higher TN and TP concentrations than that of Wulongchi stream. In temporal scale, TN concentrations during the flooding season were higher than those during the dry season, while the situation was opposite for TP. The mean mass fraction of NH4(+) -N/TN was 69% in Shendinghe River, while 20% less than others. As for nitrate nitrogen (NO3(-) -N), it ranged from 1.3 to 2.7 mg x L(-1) and the mass fractions of SRP/TP varied from 30% to 45%. All of these three tributaries were in the state of eutrophication, and nutrition stoichiometry analysis revealed that Shendinghe River was in the state of nitrogen limitation, while the river mouth area stayed in phosphorus limitation.