“人造洪峰”期间黄河入海重金属变异及影响因素研究

The implementation of water and sediment regulation to adjust the discharges of the water and sediments of Yellow River is a pioneering work in human history. This short-term “artificial flood” has deeply changed the transport patterns of the materials including heavy metals from Yellow River into the sea. The significant changes of heavy metals transport may have a significant threat on estuarine and coastal ecosystems. However, the variation of the heavy metals transport and it’s influencing factors during the flood are poorly understood at present. This project intends to carry out the water and sediment investigation and sample collection at Lijin and Huayuankou gauge during the different stages of the “artificial flood”, which are the control gauges of the water and sediments discharged from the middle reaches reservoir and into the sea, respectively. We attempt to find out the ratios of the particulate and dissolved forms of heavy metals from Yellow River, the chemical speciations of particulate metals, and then to estimate the heavy metal flux into the sea. On the basis of the study of the relationship between water physical and chemical properties, the suspended sediment features and the heavy metal transport during the flood, and the determination of the heavy metals transport differences between the reservoir discharged and into the sea, to explore the influencing factors of heavy metal transport, reveal the response of the heavy metal transportation to the process of “artificial flood”. The expected results of this study could provide scientific support for environmental protection of the Yellow River lower reaches, estuary and coastal area, as well as the optimization of the Yellow River water and sediment regulation scheme.

黄河调水调沙“人造洪峰”深刻改变了黄河入海水沙的输送状态，进而影响重金属的搬运形式和通量，对脆弱的河口生态环境造成潜在的威胁。然而迄今为止对“人造洪峰”引起的重金属输送的变异及其控制因素尚不清楚。为此，本申请项目拟针对“人造洪峰”阶段性排水、排沙的特征，选取中游水库下泄控制水文站（花园口站）和入海控制水文站（利津站），开展水体、悬浮体样品和水文数据的采集与分析工作，查明黄河入海重金属在颗粒态、溶解态间的配比和颗粒态重金属的赋存相态，估算重金属入海通量；通过对洪峰时期入海水体物理化学性质、悬浮泥沙属性与重金属输送特征关系的分析，以及花园口站和利津站重金属输送差异的对比研究，阐明“人造洪峰”期间入海重金属输送变异的主控因素，构建入海重金属输送特征对洪峰不同阶段的响应关系。预期成果可为黄河下游、河口和近海环境保护提供科学支持，并为优化黄河调水调沙方案提供参考。

自2002年开始实施的黄河调水调沙，深刻改变了黄河入海水沙的输送状态，进而影响重金属的搬运形式和通量，对河口以及渤海的生态环境产生深远影响。本项目通过对“人造洪峰”前后、行洪、排沙及洪峰末期等不同阶段黄河入海重金属的研究，结合小浪底水库和黄河口沉积物的调查分析，查明了洪峰不同阶段重金属的输送形态、入海通量和主要来源，构建了重金属输送的源汇过程及其对洪峰阶段性过程的响应关系，阐明了制约洪峰期间重金属输送的影响因素。结果表明，该期间黄河入海物质组成、重金属及同位素、有机碳氮及其同位素等的输送与来源等与调水调沙实施阶段有着良好的响应关系。在调水调沙第一阶段入海径流量和悬沙浓度较高，悬浮沉积物粒径增大，溶解态和颗粒态重金属含量较高；第二阶段水沙通量逐步减小，悬浮沉积物进一步增粗，溶解态和颗粒态重金属含量持续减小。2015年该阶段黄河入海重金属通量占到全年的42.4%~54.2%，重金属输送以颗粒态为主。溶解态重金属不仅继承了中上游水库的特征，也受到了下游河道沉积物释放的影响，颗粒态重金属则以下游河床冲刷来源为主。小浪底水库、利津站、黄河口沉积物中Pb同位素组成均符合黄河源Pb演化规律，在调水调沙前期和后期，受到中上游沉积物来源影响，含量和同位素组成较高；在调水调沙中间的主要时段，Pb主要来自洪水对下游河床的冲刷。2018年调水调沙期间，POC与PN含量随着输沙量的增大和洪峰的到来，含量迅速升高，δ13C发生较大负偏，与下游河道的粗颗粒植物碎屑冲刷有关；第二阶段POC与PN始终保持较高水平，主要来自小浪底水库沉积物；末期明显下降并基本稳定。调水调沙期间重金属的搬运特征受到黄河水沙通量、沉积物性质（碳酸盐含量、矿物组成、有机碳氮组成）等的重要影响。本研究对认识强人类活动影响下大河流域-海岸带之间的物质交换作用及重金属的“源-汇”过程具有重要的科学价值，可为黄河下游、河口以及近海海洋环境的可持续发展提供科学依据。