感潮河口重金属的沉积物通量与反应模型

Content and speciation of heavy metals in water and sediment of estuaries is dominated by the complex hydrodynamic, sediment, and biogeochemical processes as a result of dynamic river runoff and tides and has important implication for coastal ecosystem health. This project will study the dynamic exchange of heavy metals [arsenic (As) and lead (Pb)] on water-sediment interface in tidal estuary of heavily polluted Xiaoqing River using numerical hydrodynamic and water quality model, in-situ measurement and sample analysis, as well as laboratory experiments. Continuous measurement during dry, flood, and average flow season will be performed at multiple sites to determine the river bottom shear stress, sediment deposition-resuspension, dynamic variation of temperature, salinity, and pH gradient, as well as the gradient diffusion of As and Pb on sediment interface. Laboratory experiments will be conducted to simulate the kinetic retention and release of As and Pb in sediment at different pH and ionic strength. Analysis will be carried out to determine the physical and chemical speciation of As and Pb in.various depth of overlying water, pore water, and sediment layers. The sediment flux model will be constructed by coupling hydrodynamic model (EFDC) and water quality model (WASP) to simulate the source-sink relationship of As and Pb under various environmental conditions and provide scientific support for ecological risk and damage assessment as well as planning for pollution control.

河口的径流与潮汐动态及其作用下复杂的水动力、沉积和生物地球化学过程，共同控制着水体和沉积物中重金属含量和形态分布，对近海生态系统健康有重要影响。本项目结合数值水动力水质模型、现场观测和采样分析、及室内模拟试验，共同阐明水动力和生物地球化学梯度影响下重金属（砷和铅）在山东省小清河感潮河口沉积物界面的交换与反应过程及其关键控制因素。具体计划如下：在河流枯平丰季进行多站位现场连续观测，确定潮周期内河床底部应力和沉积物沉降与再悬浮过程，分析界面温盐和pH梯度的动态变化，测定砷铅的梯度扩散；应用动力学实验确定不同pH 和盐度梯度下沉积物中砷铅吸收和释放速率；分析不同层次的上覆水、孔隙水与沉积物中砷铅的物理和化学形态分布；耦合水动力模型(EFDC)和和水质模型(WASP)建立感潮河段的沉积物通量模型，确定砷铅在不同环境条件下的交换和输运通量，服务于生态风险与损害评估及污染控制规划决策。

本项目以山东省小清河感潮河段为研究对象，结合现场观测和采样分析、室内模拟试验和数值水动力水质模型，阐明水动力和生物地球化学梯度影响下重金属、抗生素等污染物在感潮河口的迁移机制与传输过程，服务于生态风险与损害评估及污染控制规划决策。主要成果与结论如下：. （1）总结和分析了“流域-河口”系统重金属输运机制与模拟的国内外研究动态。针对小清河河口的研究发现：水体（表层和底层）中As和Sb浓度在枯水期和平水期沿王道闸向河口方向呈逐渐降低趋势；丰水期As和Sb浓度明显低于枯水期和平水期，但丰水期王道闸开启后上游河水携带的悬浮颗粒物会导致As和Sb的释放，使二者浓度在河口下游出现增大情况。沉积物孔隙水中的As浓度明显高于河水，沉积物表现出As释放的特征；孔隙水中Sb浓度与河水相差不大。. （2）以罗丹明B为示踪剂开展了小清河河口的现场示踪试验。结果发现：海水至少能够上溯到王道闸下游12.5 km处，即水位变化和电导率值变化相对应。由于河流径流量较小以及潮汐的阻碍作用，示踪剂在河口向海方向的迁移较为缓慢。. （3）小清河As的入海通量约2.62 吨/年，Sb的入海通量约2.68吨/年。总体而言，小清河水体中As和Sb浓度较低，但常年持续输入可能已经造成莱州湾沉积物中As和Sb累积，进而危害海洋生态环境。未来将聚焦于对莱州湾水体和沉积物中重金属含量、分布及生物毒性问题的研究。. （4）污染较重的7种抗生素（SMX、TMP、CIP、OFL、ETM、SMZ、RTM）在河口水体中的检出率均高于沉积物。抗生素的空间分布受潮汐的控制。室内模拟试验表明：SMX、CIP和TMP在水体中主要通过光解反应发生降解，当三种抗生素进入河口水环境后，首先通过吸附过程发生快速、不同程度地衰减；随后发生较为缓慢的光解和生物降解反应，使其浓度进一步衰减。模型模拟结果表明：抗生素在河口上游的迁移主要受河流径流控制，受潮汐的影响相对较小；越接近莱州湾，潮汐对抗生素迁移的阻碍越明显，抗生素在河口下游滞留的时间也越长。