Distribution Characteristics of Nitrogen and Phosphorus in the Backwater of Typical Tributaries Under the Interaction of Main Stream and Tributaries in the Three Gorges Reservoir
After the impounding of the Three Gorges Reservoir,flows from the tributaries formed the backwater area.It is important to understand the distribution characteristics of nitrogen and phosphorus in the backwater under the interaction of main stream and tributaries for a better understanding of the formation mechanism of tributary algae bloom.Xiangxi River,a typical tributary of the Three Gorges Reservoir,was taken as the study object.The distribution characteristics of nitrogen and phosphorus concentration,composition and N/P ratio were analyzed by stratified sampling in the backwater area during flood period and storage period.The results showed that during flood seasons,the water body showed vertical stratification,TP(0.04-0.33 mg/L),TN(0.57-2.36 mg/L)and NH3-N(0.03-0.20 mg/L)were higher in the upstream and estuarine than that in the middle reach.DTP(0.01-0.23 mg/L),DTN(0.2-2.0 mg/L)and NO3-N(0.96-1.77 mg/L)decreased gradually from upstream to downstream.The phosphorus was mainly in the form of particles(DTP/TP 0.13-0.19),and nitrogen was mainly in dissolved state(DTN/TN 0.88-0.91).The N/P ratio(TN/TP 1.3-139)was the highest in the middle.During storage periods,the vertical stratification was weakened,and the difference of nitrogen and phosphorus concentration was decreased(TP 0.05-0.17 mg/L,TN 1.48-1.91 mg/L).Nitrogen and phosphorus were mainly in the dissolved form(DTN/TN 0.57-0.77,DTP/TP 0.63-0.68).N/P ratio(TN/TP 23-86)gradually decreased from estuary to upstream.The gradient difference of N and P was more significant in flood seasons than in storage seasons.The decrease of sediment particle recharge from the Yangtze River main stream during impoundment periods resulted in a higher proportion of dissolved nitrogen and phosphorus than that in flood seasons.The change of N/P ratio may be resulted from the combined effects of the main stream overburden,the sedimentation of sediment particles and the upstream inputs.The results show that the interaction between main stream and tributary plays an important role in driving nitrogen and phosphorus distribution in the backwater of tributaries.
The Three GorgesXiangxi Rivermain stream and tributariesinteractionnutrientdistribution
万方数据
维普
