南黄海海域泥沙过程对污染物输移影响的诊断研究

The influences of the internal sediment motion and redistribution such as the settling and resuspension processes, and the horizontal transport of sediment on the transport and dilution of pollutants are getting focused in recent years. As an effective method for studying the water exchange and transport, transport time scale concepts could be extended to sediment related transport research. Therefore, the radial sandbanks of South Yellow Sea, which is characterized by unique and complex geography and dynamics, is chosen as the study area. And through both the laboratory sediment experiments and numerical modeling, the three-dimensional hydrodynamic and suspended sediment model is setup for South Yellow Sea area. By defining the resuspension age and transport age of sediment, both the exchange characteristics of water and sediment and the response mechanism of the intermittent settling and resuspension processes to hydrodynamics in tidal creek terrain system are studied. Moreover, by involving the Lagrangian particle tracking method, the transport differences for secondary pollution of the adsorbed state pollutants, which is due to sediment settling-resuspension processes, are studied and compared with the situation without considering sediment related processes. The achievements are expected to contribute to the basis of water-sediment exchange and sediment processes influenced transport and dilution of the pollutants, and to provide references for the application in multi-sources sewage proposal for water quality management.

含沙水体中泥沙的沉降、再悬浮过程以及水平输运对污染物输移扩散及空间分布的影响近年来越来越受到学者们的关注，而传输时间尺度作为研究水体交换和输运的一种有效手段，可拓展至泥沙相关输运过程的研究。因此，本项目拟针对动力、泥沙及地貌地形环境均较为独特和复杂的南黄海辐射沙洲海域，通过实验室泥沙实验与数值模拟相结合的方法，建立相应的三维悬沙模型；引入泥沙的再悬浮游弋时间（resuspension age）和水平输运游弋时间（transport age），研究潮沟地形水沙交换的特征及泥沙间歇性沉降-再悬浮过程对潮沟地形地貌系统中动力条件的响应规律；并通过拉格朗日粒子追踪方法，分析附着态污染物由于泥沙沉降-再悬浮过程产生的二次污染而出现的输移扩散规律的差异。预期成果可在一定程度上丰富南黄海海域水沙交换和污染物输移扩散规律的研究成果，在技术上可为沿岸多目标源污水排放的水质管理提供相应理论依据。

南黄海辐射沙脊群拥有潮沟与滩脊交错的独特地形，潮流动态环境中的露滩过程与悬沙浓度分布变化过程密切相关，而吸附污染物的悬沙通过沉降-再悬浮过程与水沙底部交界面发生充分的接触，其中随泥沙沉降的污染物会成为潜在的二次污染源，并在受到扰动后再次进入水体，因此研究考虑泥沙颗粒表面吸附作用的污染物浓度分布变化规律十分必要。本研究围绕南黄海海域泥沙过程对污染物的输移影响，开展了现场采样及室内试验、方程推导和数值模拟等几方面的工作。针对黄海区域及包括钱塘江在内的东海北部区域建立了嵌套的数值模型，复演了辐射沙脊群海域潮流动力支配下的水动力过程，通过粒子追踪法和动力系统方法中的拉格朗日拟序结构分析了点源污染物的输运形态及其与沟、脊地形之间的关系；实现了伴随方法对滞留/曝光时间的求解，并分析了辐射沙脊群海域年龄和滞留/曝光时间的分布形态和对潮汐、风等影响因子的响应规律；以磷作为代表污染物，通过磷吸附物理实验，分析了江苏沿岸泥沙代表粒径在不同磷初始浓度和不同含沙量浓度下的平衡吸附量和吸附动力关系；假设溶解态和吸附态磷在泥沙吸附作用下达到动态平衡，推导了冲淤平衡状态下考虑悬浮泥沙影响的磷迁移转化控制方程，并进一步推导了基于该方程的年龄和滞留/曝光时间的控制方程。基于以上方程在数值模型中的算法实现，比较、探讨了泥沙吸附作用在磷浓度扩散、稀释过程中的影响和作用，结果表明考虑泥沙影响后，污染物输运时间明显增大，且受泥沙吸附能力影响较为敏感，随着泥沙吸附能力增强，泥沙对污染物输运时间的影响增大，并趋于稳定。本项目的研究成果是环境泥沙学科中泥沙污染物吸附对污染物稀释扩散影响规律的有益探讨，加深了对辐射沙脊群海域污染物输运形态的认识，可作为理论参考为近岸海域水质管理、污染物排放提供有益的借鉴。