中文摘要：

河流梯级水坝建设不仅造成营养元素在水库累积,向下游的输送通量降低,而且由于对不同元素的不同拦截效率会影响到元素的计量关系,从而影响水库生态系统和水质变化。为了厘清水库对N、P的拦截效率,本研究于2013-2015年分三次对乌江流域七个大型梯级水库水体总氮（TN）和总磷（TP）浓度进行了采样分析,探讨了不同梯级水库中氮磷营养元素的分布及其滞留效率。结果发现,乌江流域各梯级水库中TN浓度从上游到下游有逐级降低的趋势,每一级水库拦截了2%-13%的氮。乌江流域梯级水库较低的生产力和较高的氧浓度使其对TP的拦截效率更高,但水库较低的TP浓度使得拦截效果容易受到外源P输入的抵消。水库对TN、TP的拦截效率差异导致水库N/P比值发生了明显变化,因而在流域管理控制N、P的方法选择上应充分考虑这一自然过程的影响。

英文摘要：

Cascade dams constructed in rivers have remarkable influences on global cycles of nutrient elements and aquatic environment through not only accumulating nutrients in the reservoirs and reducing the downstream output fluxes,but also changing the stoichiometric relations of different elements due to different retention mechanism and efficiency. In this paper,water samples were collected from seven large cascade reservoirs in Wujiang River Basin in September of 2013,July of 2014,and June of 2015; concentrations of total nitrogen（ TN） and total phosphorus（ TP） were determined,and the retention efficiency of N and P in the reservoirs were estimated. Results show that concentration of TN in the reservoirs of Wujiang River Basin gradually decrease from upstream to downstream,by 2% -13% in average,for each step reservoir. Low productivity and high oxygen concentration in the cascade reservoirs of the Wujiang river basin lead to a more efficient interception for P. However,the impact of highly-efficient retention of P is prone to be offset by exogenous P input due to the low P concentration in the reservoirs. The difference in interception efficiency of N and P in reservoirs leads to remarkable change in N︰P in the water,and consequently causes change in environment and ecology in the water. Thus,the influence of interceptionof dams should be taken into account in the watershed management of controlling N and P.