入库河流输入对密云水库磷滞留过程的影响分析

The influence of upstream input on phosphorus retention in Miyun Reservoir

上游河流输入是密云水库磷最主要的来源,目前多数研究集中在对输入负荷的估算上,但分析其对库区总磷负荷影响的研究并不多见.本文估算了2002—2011年间总磷的出、入库质量负荷,并分析了其对库区磷滞留量、滞留率和内源释放的影响.结果表明,密云水库TP入库浓度和负荷都呈现逐年降低趋势,并主要受流量的影响.出库和库区内TP负荷基本稳定,而滞留量的变化趋势与河流入库输入一致.库区TP年均滞留率达到61.4%.与许多研究结果不同的是,因密云水库大集水面积、高水位和低流量的库区特征,总磷滞留率受水力负荷和水力滞留时间的影响不大,主要决定于河流入库负荷.另外,入库负荷的降低也可能促进底泥磷的释放.因此,控制上游TP负荷输入是降低库区TP滞留量最根本的措施,但因底泥释放补给,在短时间内库区内磷含量不会出现明显降低.

Upstream input is the largest source of total phosphorus（ TP） in Miyun Reservoir. At present,although many studies have focused on the estimation of input mass loading for TN,few have analyzed the influence of input on TP load in the reservoir. In this study,we estimated the upstream and downstream TP mass and analyzed the influence of upstream input on the retention of TP,retention rate,and net sedimentation coefficient based on a 10-year（ 2002—2011） record data of TP in Miyun Reservoir. The results show that the input TP concentration and mass load had decreasing trends during these ten years,which was mainly affected by the flow rate. TP load of outflow and in the reservoir tended to be constant,but the trend of TP retention was consistent with that of inflow TP. In addition,TP retention rate in Miyun Reservoir reached 61.4% of upstream input,but was less effected by hydraulic loading rate（ HLR） and hydraulic retention time（ HRT） in the reservoir,because of the unique characteristics of Miyun Reservoir,such as huge catchment area,high water level and low flow rate. Besides,the TP release in sediment would be slower with the decrease of upstream input. Therefore,controlling the upstream input is the fundamental measure to reduce the TP in the reservoir. However,the TP content would not have an obvious decline in a short period of time due to the sediments release.