水体紊动作用下悬移质泥沙对藻毒素环境行为的影响机制研究

Eutrophication and harmful algae blooms are prevalent environmental concerns in rivers systems in China. Some of the harmful algae species can produce and release cyanotoxin into water hence pose potential threaten to the aquatic system as well as human beings. The bioavailability of cyanotoxins in river was greatly impacted by the transfer process in the sediment-water interface. In this study, with the purpose of interpreting the interface process of suspended sediment influencing the environmental behavior of cyanotoxins under flow turbulence conditions, we devoted to study the hydrodynamics, surface property of sediments and the environmental behavior of cyantoxin in a water column that stimulated a tributaries (Yulin river) of Three Gorge Regions. The nearly isotropic homogeneous turbulence in the water column was generated by an oscillating grid turbulence device, and the environmental scanning electron microscope and high-throughput sequencing technology were employed to study the impact of suspended sediment on the environmental behavior of cyanotoxins under varied flow turbulence conditions, including the adsorption/desorption property of cyanotoxin on suspended sediment, the destruction of cyanotoxins molecular through sediment shear stress, the relationship of the surface property of suspended sediment attached bacteria and environmental behavior of cyanotoxin, and the quantitative assessment of adsorption/shear/adsorption-biodegradation effects of suspended sediment on the removal of cyanotoxin. The results of this study are supposed to improve our understanding on the influence of suspended sediment on the environmental behavior of caynotoxin under flow turbulence conditions, and are helpful for making strategies to control dissolved cyanotoxin in suspended sediment-riched river, and may provide imperative information for the enhancement of water safety and human health in the watershed.

富营养化及“藻华”是我国河流主要的水环境问题。藻毒素是藻细胞的代谢产物，对水生态安全及人体健康具有潜在危害，其在河流中的生物有效性与其在泥沙/水界面的迁移转化过程紧密相关。本研究围绕水动力学、泥沙表面特性以及藻毒素环境行为，以三峡库区次级河流—御临河为原型，利用近似均匀紊流模拟装置，应用环境扫描电子显微镜成像和微生物高通量测序等分析手段，通过研究水体紊动条件下河流悬移质泥沙对藻毒素的吸附解吸性能、探讨河流悬移质泥沙剪切作用对藻毒素分子结构的破坏性能、分析泥沙附着生物膜微观特性与藻毒素在水环境中的环境行为之间的内在联系、定量解析吸附/剪切/吸附-生物降解机制对悬移质泥沙去除藻毒素的贡献，来揭示水体紊动条件下河流悬移质泥沙对藻毒素的环境效应及界面过程。研究结果将深化水动力作用对悬移质泥沙影响藻毒素环境行为机制的认识，为制定多沙河流中藻毒素的控制策略、保障流域水环境安全与居民健康提供科学依据。

本研究通过解析三峡库区次级河流-御临河在蓄泄水周期内的微囊藻毒素（MCs）的时空分布变化特征及其与环境因子的关系，阐述水动力-泥沙-藻毒素的响应模式；通过建立近似均匀紊流模拟系统（AHTS），构建紊流及悬移质泥沙共培养体系，研究紊流与悬移质泥沙耦合作用对浮游植物群落生态过程的影响，以及该条件下浮游植物群落的主动生存策略；通过解析紊动作用下河流悬移质泥沙表面微生物膜降解、吸附等过程，阐明悬移质泥沙影响藻毒素环境行为的复合过程。主要结论如下：. （1）MC-RR是御临河中MCs的主要异构体，其最大浓度为3.55 µg/L；在时间分布上，泄水期MCs浓度较高，在空间分布上，从上游河段到河口的MCs浓度呈上升趋势； MCs和悬移质泥沙含量呈负相关关系；基于风险熵值的生态风险评价结果表明，MC-LR对底栖无脊椎动物有较高的负面风险影响。泥沙是削减御临河溶解态藻毒素的重要因子，所研究断面沉积物中MCs含量比泥沙高1.70～20倍，且泥沙与沉积物具有较高的同源性，表明在水动力作用下泥沙的悬浮-沉降是影响水相中藻毒素浓度的关键过程。. （2）在紊流体系中，高紊动强度（1.80×10-2 m2/s3）提高了体系内浮游植物密度。与紊动强度为2.25×10-3 m2/s3的处理相比，高强度紊动处理促进了群体态浮游植物栅藻属（Scenedesmus sp.）的生长，微囊藻（Microcystis sp.）在高紊流下更容易存活。在紊流与泥沙共干扰体系下，紊流越高，浮游植物密度越大，且可进一步的提高群体藻的比例。另一方面，在泥沙-藻共培养期内，藻细胞释放的胞外聚合物（EPS）附着在泥沙表面，改变泥沙表面特性，形成较大尺寸和光滑表面的SPM，可减轻水体中泥沙碰撞形成的剪切力对藻细胞的损伤。. （3）悬移质泥沙表面可形成丰富的生物膜，该生物膜对藻毒素的吸附、生物降解共同导致了藻毒素的去除，但当有机质存在时，会抑制生物膜对藻毒素的吸附，进而降低藻毒素的去除效率。. 本项目的研究结果为进一步了解在水动力作用下污染物的行为及效应提供依据。