3-dimensional floc structure and dynamics

悬浮颗粒物（SPM）在水生环境中对沉积物、污染物、病原体、营养物质和人造纳米材料的影响和最终归宿发挥着重要作用。悬浮颗粒物对水生生态系统很重要，将物质从集水区转移到海岸，对营养物的地球化学循环有重大贡献，并且是海洋中向下碳通量的主要载体。水体中过多的悬浮沉积物可被视为污染物;通过增加营养物负荷和减少溶解氧浓度来降低水质，影响生态状况和英国对欧盟水框架指令的遵守。细沉积物一旦沉降，就会减少水生生物的多样性，例如使生物窒息和使砾石产卵。沉积物也会阻塞河道和港口，影响航运。例如，在英国，我们挖掘C。每年有4000万吨沉积物，耗资数百万英镑。因此，为了做出基于证据的沉积物管理决策，迫切需要了解并准确预测悬浮颗粒物在所有水生环境中的命运和运输。悬浮颗粒物以絮凝体的形式存在于水生系统中。絮凝体是由细小的沉积物颗粒、细菌、有机物和充满液体的孔隙组成的非常脆弱、松散的集合体。絮体具有非常复杂的形状和结构，并且密度非常低。当絮凝物从悬浮状态中沉淀出来时，它会不断地改变形状、大小和结构，因为它会在湍流的水中多次分解和重组。这些絮凝物的微妙性质和它们的大小（几微米到几毫米）意味着它们非常难以取样和分析。目前的分析技术，如光学或电子显微镜可以看到整个絮体，但有限的细节，或亚微米部分的絮体，他们只能看到一个二维的横截面。因此，许多预测细颗粒泥沙输运的数值模型依赖于复杂三维形状和结构的二维简化，或者必须使用数学方法来描述絮凝体结构，例如，它们假设絮凝体是分形的，并且它们的结构是自相似的，而不管尺度如何。因此，我们的了解絮凝体的结构和行为是非常有限的，除非我们可以采样和分析絮凝体在一系列的空间尺度，我们既不能支持也不能挑战这些数学assumptions.We将解决这一研究空白和采样，观察和量化沉积物絮凝体的微观结构，首次在3维和多个，相关的空间尺度从c。10纳米到毫米。这将解决如何三维絮凝体的微观结构影响悬浮颗粒物运输的基本问题。该项目整合了生物医学科学中更常用于检查脆弱生物细胞组织的采样技术，以及材料科学和地球科学中用于分析混凝土、合金和岩石微观结构的分析技术（聚焦离子束纳米断层摄影FIB-nt/SEM和X射线显微断层摄影）。然后，我们将应用这种新的方法来研究微妙的，絮凝的沉积物在水环境中。

Suspended particulate matter (SPM) plays a fundamental role in the impact, and eventual fate of sediment, pollutants, pathogens, nutrients and manufactured nanomaterials in aquatic environments. Suspended particulate matter is important to the aquatic ecosystem, transferring material from the catchment to coast, contributing significantly to the biogeochemical cycling of nutrients, and is the main vehicle for downward carbon flux in the ocean. Too much suspended sediment in the water column can be considered a pollutant; reducing water quality by increasing nutrient loads and reducing dissolved oxygen concentrations with impacts for ecological status and the UK's compliance with the EU Water Framework Directive. Once settled, fine sediment can reduce aquatic biodiversity, for example by smothering organisms and spawning gravels. Sediment can also block river channels and ports with impacts for navigation. For example, in the UK we dredge c. 40M tonnes of sediment every year costing millions £GBs. Consequently, in order to make evidence-based sediment management decisions, there is an urgent need to understand and make accurate predictions of SPM fate and transport in all aquatic environments.Suspended particulate matter exists in aquatic systems as flocs. A floc is a very fragile, loosely bound aggregate of fine sediment particles, bacteria, organic matter and fluid-filled pore space. Flocs have very complex shapes and structures, and very low density. As a floc settles out of suspension it continually changes shape, size and structure as it breaks apart and reforms many times in the turbulent water. The delicate nature of these flocs and their size (a few microns to a few millimetres) means that they are very difficult to sample and analyse. Current analytical techniques e.g. optical or electron microscopy can either look at whole flocs, but with limited detail, or sub-micron sections of a floc, and they can only look at a 2-dimensional cross section. Therefore, many numerical models that predict fine sediment transport rely upon 2-dimensional simplifications of complex 3-dimensional shapes and structures, or have to use mathematical approaches to describe floc structure e.g. they assume flocs are fractal and that their structures are self-similar irrespective of scale. Therefore, our understanding of floc structure and behaviour is very limited and unless we can sample and analyse flocs at a range of spatial scales we can neither support nor challenge these mathematical assumptions.We will address this research gap and sample, observe and quantify sediment floc micro-structure for the first time in 3-dimensions and at multiple, correlated spatial scales from c. 10 nanometres to millimetres. This will address the fundamental question of how 3-dimensional floc micro-structure influences suspended particulate matter transport. This project integrates sampling techniques from the biomedical sciences that are more commonly used to examine fragile biological cell tissues and analysis used in materials science and the earth sciences to analyse the microstructure of concrete, alloys and rocks (focussed ion beam nanotomography FIB-nt/SEM and X-ray microtomography). We will then apply this novel approach to the study of delicate, flocculated sediment in the aquatic environment.