北京山区水库水体磷和重金属表观沉降速率研究

Beijing is suffering a severe water shortage in recent decades, and this problem will be more serious in the future for water pollution. The lack of information for the delivery and transformation of pollutants at the watershed scale led to the lack of information for pollutants delivered from the upper-rivers to reservoirs. The apparent settling velocity can quantitatively represent the net effect of different processes that deliver pollutants to sediments. To estimate the apparent settling velocity of pollutants, in this present study, in the mountainous region of Beijing, water samples were collected from 4 reservoirs, the upper-rivers of them and air precipitation. Based on the method of calculating the non-point source pollution load at the field scale, records of hydrological and weather stations, data of digital elevation model, land use and land cover were collected; moreover, the pollution load of reservoir, the upper-rivers and the catchment around the reservoir were calculated. And the apparent settling velocities of phosphorus and heavy metals were calculated by means of mass balance. Based on the simulation experiment for the release of pollutants in sediment, apparent settling velocity for release of endogenous contaminants was calculated and apparent settling velocity for the transport of exogenous contaminants was estimated. Moreover, influencing factors for apparent settling velocity of phosphorus and heavy metals were discussed and distinguished. Apparent settling velocity model will be established on the basis of the influencing factors.

日益严重的水污染问题加剧了北京水资源短缺。现有研究对污染物在流域尺度内迁移转化规律尚缺乏深入认识，尚未有效建立水库水质与入库污染物之间的定量联系。表观沉降速率可定量描述污染物通过不同过程，输移进入水库沉积物的净效果。研究在北京山区选择4个典型水库，通过水库及其上游河流非点源污染监测，在提出坡面非点源污染负荷计算方法的基础上，收集水文、气象、地形和土地利用管理资料，计算水库自身和由入库河流、水库周边集水区及大气降水进入水库水体的污染物总量；利用质量守恒原理，计算水库水体磷和重金属的总表观沉降速率。同时，通过室内模拟实验，模拟底泥污染物释放过程，分析内源污染物释放对应的表观沉降速率，进而推算外源污染物运移对应的表观沉降速率，并探讨影响表观沉降速率的主要因素，建立利用主要影响因素计算本区水库水体磷和重金属表观沉降速率的模型。从而为流域非点源污染模拟提供理论支持，为水污染防治提供科学依据。

表观沉降速率是定量描述污染物通过不同过程，输移进入水库沉积物的净效果的重要参数；也可定量描述水体污染物自河道向水库的迁移过程。北京山区是北京市重要的水源地，明确污染物入库后的环境行为，对保障饮用水安全十分重要。研究在北京市密云区石匣水土保持试验站开展坡面径流小区非点源污染监测，并收集小区径流产沙观测资料，建立了坡面径流量计算模型、土壤流失量计算模型、污染物随径流流失模型、污染物随泥沙流失模型等4个子模型，以构成坡面污染物负荷计算模型。研究同时在北京山区选择了官厅、半城子、栗榛寨和黑圈等4个工程等别不同的水库，开展水库非点源污染监测，获得由入库河流和大气降水进入水库水体的污染物量，结合由坡面污染物负荷计算模型获得的水库周边集水区入库污染物量，完成物质平衡分析，计算水库水体污染物的总表观沉降速率。为从表观沉降速率中定量分离出内源和外源污染物运移分别对应的部分，研究通过室内模拟实验，分析扰动过程中和扰动结束后，底泥中污染物向水体释放状况，计算内源污染物释放对应的表观沉降速率，进而推算外源污染物运移沉降对应的表观沉降速率。最后，研究建立了总表观沉降速率与其主要影响因素之间定量关系。对于大型水库，建立了利用水温、水库蓄水量和上游来水量计算水体污染物总表观沉降速率的方程。对于中型和小型水库，建立了利用污染物初始浓度计算水体铁和锌的总表观沉降速率的方程，以及利用叶绿素a浓度计算小型水库水体磷的总表观沉降速率的方程。研究还提出了利用沉降时间计算内源污染物释放对应的表观沉降速率的方程。本研究定量刻画了污染物自周边集水区和上游河道向水库迁移的过程，及其在水库中运移沉降特征，可为流域水质模拟提供技术支持，为流域水污染防治提供科学依据。