河水位波动下潜流带非均质性对氮的迁移转化过程影响研究

The Effects Of Heterogeneity Of Hyporheic Zone On Nitrogen Migration And Transformation Under Fluctuation Of River Level

张强

11749131

硕士

环境科学与工程

张幼宽

2019-05-28

2019-07-15

哈尔滨工业大学

深圳

氮污染是土壤、地下水及地表水的重要环境问题之一。吸附在土壤中的氮素在降水入渗或农业灌溉的驱动下进入含水层并污染地下水。含水层中的氮污染物随地下水流迁移最终以基流形式排泄至地表水体，进一步加重地表水体污染。潜流带是河流生态系统中的重要组成部分，其独特的物化性质和生物特性使得潜流带内生物地球化学反应异常活跃，该特征使得潜流带具有明显的消减氮污染物的能力。潜流带水动力过程是生物地球化学反应的重要驱动力。降水、洪水和大坝的调蓄泄洪等作用会引起河水位瞬时上升，导致潜流带内水动力过程存在明显的动态特征。受复杂的沉积作用影响，潜流带的介质通常存在非均质性。潜流带的非均质性会形成复杂的流场分布，从而影响潜流带氮污染物的生物地球化学反应过程。本论文选取河流-潜流带剖面为研究对象，基于PFLOTRAN建立二维变饱和水流数值模型，模拟在河水位正弦波动（周期为1天）和考虑潜流带非均质性（协方差为指数的随机分布）的条件下，地下水位、地下水流速度及河流-潜流带水量交互的动态特征。基于水流模型，重点考虑DO、DOC、NO3-和NH4+的生物地球化学反应机理，利用PFLOTRAN建立地下水氮污染物的迁移转化模型。模拟潜流带氮污染物的多组分和多过程的生物地球化学反应及迁移，探寻DO、DOC、NO3-和NH4+时空变化规律，计算潜流带的NO3-消减速率，研究河水位波动及非均质性对潜流带氮污染物生物地球化学反应的影响。研究结果表明，潜流带具有消减NO3-的能力。河水位波动振幅从0.3 m增加至0.7 m时，潜流带对NO3-的消减率从7.3 %增加至9.8 %。潜流带对NO3-的消减率随着河水位波振幅增加而增加。河水位波动下，均质潜流带与河流水流交换量最大为0.41 m3/m/h。非均质潜流带与河流水流交换量最大为0.36 m3/m/h。非均质性降低河流-潜流带水流交换量。在一个河水位波动周期，均质潜流带地下水NO3-的消减率及平均消减速率分别为8.6%和4.09 g/m/d，非均质潜流带地下水NO3-的消减率及平均消减速率分别为6.4%和2.62 g/m/d。潜流带的非均质性降低了NO3-的消减率及消减速率。研究结果对氮污染物在潜流带的迁移转化规律深入理解具有借鉴意义。

Nitrogen pollutions of soil, groundwater and surface water are global environmental problems. Irrational uses of a large amount of nitrogen fertilizers lead to severe pollutions in the soil, groundwater and surface water. The nitrogen percolates into the groundwater through the soil along with recharge processes, then the nitrogen in the groundwater is discharged to the river, which further aggravates the nitrogen pollution in the river. The hyporheic zone is an important part of the river ecosystem, which plays an important role in removing nitrate from rivers and reducing the nitrate transport downstream. The water flow in the hyporheic zone is the driving force of multiple biogeochemical processes. Precipitations, floods, and dam releases can cause periodic fluctuations of the river stages. Under natural conditions, the hyporheic zone is usually heterogenous, which results in the complicated flow field in the zone and significantly affects the biogeochemical reaction process of nitrogen. In this study, a two-dimensional numerical model, which couples variable saturated flow and reactive transport of the nitrogen, was proposed using PFLOTRAN. In this model, the effects of the river stage fluctuation and the heterogeneity of the hyporheic zone on the nitrogen transport and reaction were studied. First, the dynamic characteristics of the groundwater levels, groundwater flow velocities, exchanges of the river-aquifer, and nitrogen concentrations were investigated. Then, the nitrate removal efficiency and nitrate removal rate in the hyporheic zone were calculated. Finally, the influences of the amplitude of the river stage fluctuation and the heterogeneity of the hyporheic zone on the biogeochemical reaction were analyzed. The results indicate that the hyporheic zone has the ability to remove nitrate. As the amplitude of river stage fluctuations increased from 0.3 m to 0.7 m, nitrate removal efficiency in the hyporheic zone increased from 7.3% to 9.8%. In a period of fluctuation of river stage, the nitrate removal efficiency and nitrate removal rate in the homogeneous hyporheic zone are 8.6% and 4.09 g/m/d, respectively. By contrast, the nitrate removal efficiency and nitrate removal rate in the heterogeneous hyporheic zone are 6.4% and 2.62 g/m/d, respectively. The heterogeneity of the hyporheic zone reduces the nitrate removal efficiency and nitrate removal rate. The results of this study can be used to further understand the transport and reaction of nitrogen in hyporheic zones.

氮污染 潜流带 河水位波动 非均质性 生物地球化学反应 数值模拟

nitrogen pollution hyporheic zone river stage fluctuation heterogeneity biogeochemical reactions numerical simulation

中文

联合培养

南方科技大学

张强. 河水位波动下潜流带非均质性对氮的迁移转化过程影响研究[D]. 深圳. 哈尔滨工业大学,2019.