闸控河流潜流带营养盐运移转化机制研究

Hyporheic zone is an important "accumulator" of nutrients in river. Unlike natural rivers, nutrients in hyporheic zone of the sluice-controlled rivers are constantly transformed between dissolved, suspended and sedimentary facies under the influence of sluice regulation.Moreover, the effects of the discharge regulation and storage regulation of the sluice on nutrient transport and transformation in hyporheic zone are heterogeneous.Therefore, it is of great significance to study the transport and transformation mechanism of nutrient in hyporheic zone of the sluice-controlled river for water pollution control and water environment restoration. Firstly, under the different regulation mode of the sluice gate, the In-situ sediment collection experiments will be carried out to study the distribution characteristics of nutrients in hyporheic zone among the dissolved, suspended and sedimentary facies. Secondly, a multi-phase medium transformation model will be constructed to quantitatively study the process of nutrient transport and transformation in the multi-phase medium of "dissolved-suspended-sedimentary facies", and disscuss the influence of the sluice regulation on nutrient transport and transformation in hyporheic zone, identifies the key influencing factors, and clarifies the mechanism of the nutrient transport and transformation in hyporheic zone of the sluice-controlled river. Thirdly, combined with algae monitoring experiments, the response of algae growth to nutrient transport and transformation in hyporheic zone of sluice-controlled river will be explore to reveal the ecological risk of eutrophication faced by the sluice-controlled rivers, so as to provide basic support for alleviating the adverse effects of nutrients in hyporheic zone of sluice-controlled rivers.

潜流带是河流水体营养盐重要的“蓄积库”。不同于自然河流，闸控河流潜流带营养盐受闸坝调控的影响不断地在溶解相、悬浮相、沉积相之间发生着相态转化，且闸坝泄水调控与蓄水调控方式对潜流带营养盐的运移转化影响具有异质性，开展闸控河流潜流带营养盐运移转化机制研究对河流水污染治理及水环境修复具有重要意义。本项研究以闸坝调控为背景开展原位沉积物采集实验，探索闸控河流潜流带营养盐在“溶解相—悬浮相—沉积相”多相介质中的分布特征；构建多相介质转化模型，定量化研究潜流带营养盐在“溶解相—悬浮相—沉积相”多相介质中的运移转化过程，探讨闸坝调控对潜流带营养盐运移转化的影响，辨识关键影响因素，明晰闸控河流潜流带营养盐迁移转化机制；结合藻类监测实验，探索闸控河流藻类生长对潜流带营养盐运移转化过程的响应关系，揭示闸控河流面临的富营养化生态风险，以期为缓解闸控河流潜流带营养盐对河流造成的不利影响提供基础支撑。

本项目在沙颍河槐店闸蓄水调控（非汛期）和泄水调控方式（汛期）下实施了野外原位沉积物采集和藻类监测实验，分析了潜流带营养盐（氨氮、硝酸盐氮和TP）纵、垂向分布规律，明晰了闸坝调控的影响作用与机理；研发了水质多相转化模型，模拟了不同闸控情景下营养盐多相介质间的运移转化过程，揭示了闸控河流潜流带营养盐运移转化机制；分析了藻类生长对沉积物-水界面营养盐运移转化的响应关系，识别了影响藻类生长的关键因子及关键运移转化过程，提出了缓解闸控河流富营养化生态风险的途径。结果表明：①潜流带溶解相与表层水之间存在着较大的TP、氨氮浓度差，有利于潜流带溶解相TP、氨氮向表层水运移；蓄水调控（非汛期）会造成氨氮和TP在闸下沉积相中的累积，特别是S2、S4沉积物是氨氮、TP累积的主要场所；泄水调控（汛期）有利于S2、S4孔隙水氨氮的运移转化的同时，也利于沉积物TP向孔隙水释放。②蓄水调控（非汛期）和泄水调控（汛期）方式均对闸下河道产生了影响，特别是对闸下S2，影响最大；内源氨氮是蓄水调控（非汛期）方式下闸控河道主要内源风险源；控制内源TP释放与再悬浮是泄水调控（汛期）防止水体二次污染的关键。③构建的水质多相转化模型Nash效率系数均在0.5以上，模型模拟精度满足要求；闸门关闭时，营养盐以吸附、沉降、还原作用为主导在“溶解相-沉积相-生物相”间发生转化，而闸门开启时，营养盐以再悬浮、解吸、氧化作用为主导在“溶解相-悬浮相-沉积相”间不断进行迁移转化。④上覆水、沉积相与孔隙水硝酸盐氮是蓄水调控（非汛期）下影响藻类生长的关键因子，沉积相与孔隙水氨氮、悬浮相与孔隙水硝酸盐氮是泄水调控（汛期）下影响藻类生长的关键因子；沉积物-水界面“沉积相-溶解相”之间、“沉积相-悬浮相-溶解相”之间含氮营养盐的运移转化过程分别是蓄水调控（非汛期）和泄水调控（汛期）方式下影响藻类生长的关键环节。⑤减少外源污染物输入、疏浚氮磷富集水域（S2）底泥、优化闸坝调度方式是改善槐店闸河道水环境的主要途径。本研究为缓解闸坝对水环境造成的不利影响提供了基础支撑，对闸控河流水环境修复与保护具有重要意义。