Structure of Aquatic Flocs using Correlative Volumetric Microscopy
J. A. T. Wheatland1, 2, I. G. Droppo3, K. L. Spencer2, A. J. Bushby1
1
The NanoVision Centre, Queen Mary, University of London, UK The Centre for Micromorphology, Queen Mary, University of London, UK 3 Environment Canada, Burlington, Ontario, Canada
[email protected] 2
Within natural aquatic systems suspended sediment is typically present as flocs, irregularly shaped structures consisting of microbial cells, bioorganic matter, inorganic particles, and fluid-filled pore space [1]. The physical properties of flocs dictate the hydrodynamic behaviour of their constituents and the stability of the landforms they create once settled. Accurate quantification of floc properties is therefore critical for predicting the fate of sediment and sediment-bound contaminants. However, due to their fragile and multi-scale structure, floc characterisation has proven problematic. Research has tended to focus on measuring floc gross-scale (> 1 µm) properties, providing valuable insights into their outward (emergent) behaviour. However, this fails to inform on their internal micro- and nano-scale properties responsible for much of their behaviour and development. In this study correlative volumetric microscopy (or correlative tomography [2]), a multi-modal, multi-scale imaging strategy, is employed to facilitate floc characterisation from the centimetre to nanometre-scale. This is achieved by threading together 3D micro-CT and focused ion beam nano-tomography with 2D transmission electron microscopy. Co-visualisation of the correlative datasets enables the multi-scale properties of flocculated sediment to be explored, and a conceptual model describing floc structural hierarchy to be developed. The conceptual model highlights the influence of floc micro- and nano- structure on their gross-scale characteristics, revealing the importance of organic material and floc colonising bacteria to floc development. [1] I. G. Droppo. 2001, Hydrological Processes 15 (9) 1551 – 1564. [2] T. L. Burnett, et al. 2014, Scientific Reports 4 (1711) 1 – 6. Keywords: Flocs, flocculation, suspended sediments, correlative volumetric microscopy, correlative tomography.
