调水工程调蓄水库沉积物耗氧对环境因素响应机理及模型研究

Lots of regulating reservoirs have been constructed for water transfer project in China, however, some of those reservoirs have water quality problems such as oxygen depletion in the bottom layer. Sediment Oxygen Demand (SOD) which may cause oxygen depletion in the bottom layer is usually affected by environmental factors. During the operation period of regulating reservoirs, these environmental factors will tend to more complexes caused by the store and supply of water. Thus the response mechanism and modeling of SOD to environmental factors in regulating reservoirs need to be study in depth. In this study, Beitang Reservoir was chosen as the typical regulating in the middle line of the south-to-north water transfer project. The proposes of this study are (1) to develop a robust aquatic Eddy Correlation measurement system and implement a long-acting in situ measurement about SOD cooperate with other environmental factors using this system, (2) to process observed data and make a statistic analysis about the driving factors of SOD during the dynamic variation using LARS-Lasso (Least absolute shrinkage and selection operator) method, (3) to improve the SOD model to reflect the driving forces of environmental factors including a SOD model with sulfide - methane composite products for quantitatively describing the sulfide and methane produced in carbon diagenesis, a module to investigate under which conditions the effect of nutrient above the sediment surface on SOD becomes significant, and a function to make the association between SOD and velocity in bottom layer. The result of this study can be easily imaged to enrich the scientific understanding of oxygen consumption mechanism, especially for sediment that is low in nutrient and high in salinity. Furthermore, the importance practical significance in SOD research on other regulating reservoir cannot be neglected.

在调水工程大规模兴建的背景下，保障工程配套调蓄水库的水质安全至关重要。调蓄水库周期性调蓄使水库内影响沉积物耗氧（SOD）的环境因素趋于复杂，而当前研究缺乏长效的SOD原位测量方法和有关SOD对环境因素响应机理的阐述。因此有必要从原位测量技术、驱动因素分析和数值模拟等方面深入研究多环境因素耦合作用下调蓄水库SOD动态响应机理。本项目以南水北调中线工程调蓄水库―北塘水库为研究对象，基于涡度相关技术开发高鲁棒性SOD长效原位测量系统，利用该系统对水库SOD与环境因素协同变化进行原位测量；应用LARS-Lasso等统计方法系统分析原位测量结果，阐明调蓄水库各运行阶段SOD动态变化的主要驱动因素，揭示SOD对环境因素响应机理；建立多环境因素耦合驱动的SOD数学模型，提高现有SOD模型的模拟精度与适用性。项目成果将丰富科学界对沉积物耗氧机理的认知，对保障调蓄水库水质安全具有重要的现实意义和应用前景。

沉积物耗氧对水生生物的生存、水体自净功能的维持等具有重要影响。调蓄水库周期性调蓄使水库内影响沉积物耗氧的环境因素趋于复杂，因此探究水库调蓄过程中沉积物耗氧变化规律对保障供水水质安全具有重要意义。本研究构建了高鲁棒性沉积物氧通量长效原位测量系统，采用室内试验研究沉积物氧通量与水动力要素的响应机理，通过现场试验研究调蓄水库沉积物氧通量与水库调度及库内环境要素变化间的响应关系，揭示水库沉积物氧通量动态变化规律。主要研究内容和结论包括：（1）为保证系统的鲁棒性与量测精度，采用ADV与ARO-EC构建沉积物氧通量原位观测系统，两装置适宜水平间距为0.5-2cm，适宜采样体高度为4-5.5cm。（2）氧通量与扩散边界层厚度呈负相关关系，当扩散边界层厚度小于0.5mm时，扩散边界层厚度变化对氧通量影响更强烈，当厚度大于0.5mm后，氧通量基本保持稳定。（3）水动力条件对扩散边界层厚度的影响明显，扩散边界层厚度与Batchelor尺度呈正相关关系，实际应用中可采用Batchelor尺度近似表示扩散边界层厚度。（4）调蓄水库沉积物氧通量与水库运行形成的水动力特征与水温结构关系密切，其中氧通量与水动力要素间响应关系与室内试验结果基本一致。（5）温度对沉积物氧通量的影响规律可用Schmidt系数进行衡量，氧通量在高温区与低温区呈现截然相反的变化规律。（6）沉积物氧通量与库底处溶解氧浓度呈正相关，库底溶解氧浓度越大，沉积物氧通量越大。本项目发表/录用论文8篇，参加国内外学术会议5人/次，培养研究生1名；项目负责人入选天津市“131”创新型人才培养工程第三层次人选以及“北洋学者·青年骨干教师计划”培养对象；课题研究成果获第九届全国水力学与水利信息学大会优秀青年论文奖。