Peatlands are the second largest global store of carbon and represent the most efficient terrestrial carbon store on the planet. ~13% of the world’s blanket peatlands are located in the UK, and they play a potentially crucial role in regulating climate. It is estimated that they store ~3.12 billion tonnes and sequester ~5.5 million tonnes of carbon per year, equivalent to ~1% of the UK’s total annual greenhouse gas emissions. However, unsustainable anthropogenic exploitation of blanket peatlands has resulted in ~90% of the known extent in the UK categorised as being in poor condition under the Joint Nature Conservation Committee standards. This is a consequence of these peatlands experiencing cutting, overgrazing, burning, drainage, and erosion. Due to these anthropogenic disturbances, UK blanket peatlands are suggested to emit ~10 million tonnes of carbon per year, representative of ~2% of the UK’s total annual greenhouse gas emissions. In response, the UK Government has incorporated peatlands in national level policy through the setting of restoration targets under climate change commitments. However, restoration targets are not being met and there are no ‘hard’ policies for blanket peatland restoration specifically. This is partly due to a lack of primary research into the effectiveness of peatland restoration.This study explores the interactions between peat structure and peat function, which is indicative of carbon sequestration and storage (carbon dynamics), in restored blanket peatlands under different treatments and timescales in Cumbria, England. 3D X-ray Micro-Computed Tomography (µCT) is applied to peat core samples from natural, degraded, and restored blanket peatlands to visualise and quantify the internal structure of peat soils at a 0.51µm resolution. Structures include; 1) air filled and water filled pore networks; 2) air filled and water filled root networks; 3) peat matrix density; and 4) other organic matter developments which regulate the carbon dynamic function of peat soils. For the first time, this study will identify and evaluate the impact of blanket peatland restoration on peat structure and function. The investigation is also reinforced with bulk chemical and field monitoring datasets. These are integrated with the µCT outputs to understand the response of carbon dioxide and methane dynamics to blanket peatland restoration.

Clay-rich flocculated suspended sediments are an important constituent of estuarine and coastal systems globally. They are responsible for the host, movement and deposition of a variety of pollutants, contaminants and sediment itself. Accurate modelling of the movement of these sediments is crucial for a number of industries including fisheries, aquaculture, shipping and waste management. This requires an accurate and reliable measurements of the physical properties of flocs and their behaviour. Porosity is a key element in floc structures, and this research provides updated 3D quantified porosity and pore space morphological data in relation to influences on floc settling behaviour. We report the questionable relationship between floc size and settling velocity, and explore alternative influences such as floc composition, porosity and pore morphology. These outcomes suggest that a shift in focus from floc size to a combination of factors is necessitated to understand the complex movement behaviour of flocculated suspended sediments.

Flocculated suspended sediments (flocs) are found in a variety of environments globally, and their transport and behavior bear substantial importance to several industries including fisheries, aquaculture, and shipping. Additionally, the modelling of their behavior is important for estuarine and coastal flood prediction and defence, and the process of flocculation occurs in other unrelated industries such as paper and chemical production. Floc porosity is conventionally assessed using inferential indirect or proxy data approaches. These methods underestimate floc porosity % by c. 30% and cannot measure the micro-scale complexity of these pore spaces and networks, rendering inputs to models sub-optimal. This study introduces a novel 3D porosity and pore space quantification protocol, that produces directly quantified porosity % and pore space data.•3D floc data from micro-CT scanning is segmented volumetrically•This segmented volume is quantified to extract porosity and several pore space parameters from the floc structure

Natural sediment flocs are fragile and highly heterogeneous aggregates of biogenic and minerogenic material typically with high porosity and low density. In aquatic environments dominated by fine, cohesive or mixed sediments they can dominate suspended sediment flux. Consequently, monitoring and modelling the behaviour, transport and distribution of flocs is very important for many aquatic industries, maintenance of waterways and conservation and management of aquatic waterbodies. Mathematical models that predict the behaviour of flocs rely on the accurate assessments of the size, shape, density, porosity and fractal dimension of flocs. These inherently 3-dimensional (3D) characteristics are typically derived from 2-dimensional (2D) data, largely due to the challenges associated with sampling, capturing, imaging and quantifying these fragile aggregates. We have developed new volumetric microscopy techniques which can quantify 3D internal and external structures and characteristics of sediment flocs. Here, these techniques were applied to quantify the 3D size (volume), shape and fractal dimension of natural and artificial sediment flocs and compare them to standard 2D approaches. Our study demonstrates that 2D approaches are under-estimating shape complexity and over-estimating the size and mass settling flux of flocs by up to two orders of magnitude, and the discrepancy between 2D and 3D is most marked for natural, organic rich macroflocs. Our study has significant implications for estimations of sediment flux at local to global scales within in aquatic environments. These new data and approaches offer the potential to improve the current parameterisation of sediment transport models and to improve the accuracy of current field-monitoring techniques.

Purpose Flocculated cohesive suspended sediments (flocs) play an important role in all aquatic environments, facilitating the transport and deposition of sediment and associated contaminants with consequences for aquatic health, material fluxes, and morphological evolution. Accurate modelling of the transport and behaviour of these sediments is critical for a variety of activities including fisheries, aquaculture, shipping, and waste and pollution management and this requires accurate measurement of the physical properties of flocs including porosity. Methods Despite the importance of understanding floc porosity, measurement approaches are indirect or inferential. Here, using μCT, a novel processing and analysis protocol, we directly quantify porosity in natural sediment flocs. For the first time, the complexity of floc pore spaces is observed in 3-dimensions, enabling the identification and quantification of important pore space and pore network characteristics, namely 3D pore diameter, volume, shape, tortuosity, and connectivity. Results We report on the complexity of floc pore space and differentiate effective and isolated pore space enabling new understanding of the hydraulic functioning of floc porosity. We demonstrate that current methodological approaches are overestimating floc porosity by c. 30%. Conclusion These new data have implications for our understanding of the controls on floc dynamics and the function of floc porosity and can improve the parameterisation of current cohesive sediment transport models.

Salt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea-level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near-instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales. Whilst important advances have been made in understanding how specific soil properties affect near-instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. (c) 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Natural sediment flocs are fragile, highly irregular, loosely bound aggregates comprising minerogenic and organic material. They contribute a major component of suspended sediment load and are critical for the fate and flux of sediment, carbon and pollutants in aquatic environments. Understanding their behaviour is essential to the sustainable management of waterways, fisheries and marine industries. For several decades, modelling approaches have utilised fractal mathematics and observations of two dimensional (2D) floc size distributions to infer levels of aggregation and predict their behaviour. Whilst this is a computationally simple solution, it is highly unlikely to reflect the complexity of natural sediment flocs and current models predicting fine sediment hydrodynamics are not efficient. Here, we show how new observations of fragile floc structures in three dimensions (3D) demonstrate unequivocally that natural flocs are non-fractal. We propose that floc hierarchy is based on observations of 3D structure and function rather than 2D size distribution. In contrast to fractal theory, our data indicate that flocs possess characteristics of emergent systems including non-linearity and scale-dependent feedbacks. These concepts and new data to quantify floc structures offer the opportunity to explore new emergence-based floc frameworks which better represent natural floc behaviour and could advance our predictive capacity.

The vulnerability of saltmarshes to lateral erosion at their margin depends on the local biogeomorphological properties of the substrate. In particular, the 3D architecture of pore and root systems is expected to influence shear strength, with repercussions for the wider‐scale stability of saltmarshes. We apply X‐ray computed microtomography (μCT) to visualize and quantify subsurface structures in two UK saltmarshes at Tillingham Farm, Essex (silt/clay rich substrate) and Warton Sands (sand‐rich substrate), with four types of ground cover: bare ground, Spartina spp , Salicornia spp and Puccinellia spp . We extracted μCT structural parameters that characterize pore and root morphologies at each station, and compared them with field measurements of shear strength using a principal component analysis and correlation tests. The 3D volumes show that species‐dependent variations in root structures, plant colonization events and bioturbation activity control the morphology of macropores, while sediment cohesivity determines the structural stability and persistence of these pore structures over time, even after the vegetation has died. Areas of high porosity and high mean pore thickness were correlated to lower values of shear strength, especially at Tillingham Farm, where well‐connected vertical systems of macropores were associated with current or previous colonization by Spartina spp . However, while well‐connected systems of macropores may lower the local deformation threshold of the sediment, they also encourage drainage, promote vegetation growth and reduce the marsh vulnerability to hydrodynamic forces. The highest values of shear strength at both sites were found under Puccinellia spp , and were associated with a high density of mesh‐like root structures that bind the sediment and resist deformation. Future studies of marsh stability should ideally consider time series of vegetation cover, especially in silt/clay‐dominated saltmarshes, in order to consider the potential effect of preserved buried networks of macropores on water circulation, marsh functioning and cliff‐face erosion.

Subsurface structures and especially the interactions between pores, roots and other organic matter elements have a strong impact on ecosystem functioning. Yet despite recent progress in the application of X-ray Computed Microtomography (mu CT) to soil structure in agricultural science, applications to the more complex and heterogeneous substrates found in natural soils, specifically wetland soils, remain sparse. We apply X-ray mu CT to a complex hetemgenous soil and develop a robust segmentation method to quantify the pores, live roots and necromass. This approach significantly improves the detection of the organic matter elements, and gives us unprecedented detail and resolution in the segmentation of pores, live roots and necromass at a high spatial resolution (62.5 mu m in this study). We identify several situations where pores and organic matter interact in the soil, including the disconnected air spaces (aerenchyma) that run within the Spartina stem and roots, tubularshaped pores left behind by decaying roots, and lateral roots deploying within structural fragilities in the sediment. The capacity of X-ray mu CT to distinguish the connected live root system from the necmmass opens possibilities for applications to determine key wetland soil functions such as soil cohesivity, soil nutrient exchanges and soil carbon dynamics.

Salt marshes provide diverse ecosystem services including coastal protection, habitat provision and carbon sequestration. The loss of salt marshes is a phenomenon that is observable on a global scale and is of great socioeconomic concern due to the substantial benefits these environments provide. The causes of spatial variability in rates of marsh loss are inadequately understood for the purposes of predicting future ecosystem functions and distributions in the context of global environmental change.We investigate the relationship between vegetation of different genera and the mechanical properties of the substrate. We couple in-situ and laboratory tests of substrate geotechnical properties with micro-CT imaging of undisturbed root network structures to assess the contribution of three halophytes to sediment stability. We investigate the role of Puccinellia spp., Spartina spp. and Salicornia spp. in the modification of geotechnical parameters such as critical shear strength and cohesion when compared to un-vegetated sediments. We then compare these effects between clay-rich and sandy contexts on the East and West coasts of the United Kingdom respectively.We find that the three genera are characterised by different root network morphologies which, in part, explain the differences that we observe between the geotechnical properties of sediments colonised by these contrasting vegetation types. The presence of roots within the sediment structure increases the cohesion, as measured using a laboratory shear box test, when compared to bare sediment, with the magnitude of this effect varying by root morphology and sedimentology. In-situ shear vane tests reveal a localised spatial variability in sediment shear strength that is related to halophyte species distributions. This allows multispectral UAV imagery to be used to map species distributions and thereby infer a component of the sediment’s vulnerability to erosion that supports the prediction of future marsh distributions and, ultimately, ecosystem service provision.

Suspended particulate matter (SPM) plays a fundamental role in the impact and eventual fate of sediment, pollutants, pathogens, nutrients and manufactured nano-materials in aquatic environments. SPM usually exists in aquatic systems as flocs; complex, fragile and loosely-bound aggregates of fine sediment particles, bacteria, organic matter and fluid-filled pore space. Floc settling velocity is widely considered to be the most important dynamic characteristic that determines SPM fate and transport, and is dependent on the size, shape, density, porosity, fractal dimension and composition of the flocs formed in suspension. Of these characteristics, floc density and porosity are thought to exert the greatest impact on settling velocity, yet neither parameter can currently be measured. As such, transport model parameters are typically estimated from Stokes’ Law, based on an assumption of a spherical shape for the floc. Due to a lack of available observational data, such assumptions cannot be validated and porosity is often omitted with flocs treated as essentially impermeable spherical entities, despite pores accounting for much of the defined ‘floc-space’ (often estimated to be > 90% within larger macro-flocs). As part of a wider project exploring the 3D nature of floc structure and dynamics (NERC-3D Flocs), this study reports a first application of high-resolution 3D X-Ray microtomography on populations of flocs, offering a method that quantifies 3D floc porosity based on observation rather than assumption of floc structural properties. High resolution (3 µm voxel size) scans of both laboratory-generated and natural floc populations, from which sub-populations of different-sized micro- and macro-flocs (30 in each of 5 size categories for each floc population) are extracted. A data-processing workflow is presented which applies 3D morphological filters to systematically define a realistic expression of the total pore-space associated with individual flocs. Floc pore-space is further partitioned into isolated and effective pores, based on a 12 µm pore throat diameter threshold below which fluid flow is hydrodynamically minimal. Analysis of these realistic floc porosity data populations indicates that previous assumptions of floc porosity lack meaning in terms of settling dynamics. Substitution with meaningful, realistic floc porosity will have a significant impact on the prediction of floc settling velocity within SPM sediment transport models.

Suspended cohesive sediments form aggregates or 'flocs' and are often closely associated with carbon, nutrients, pathogens and pollutants, which makes understanding their composition, transport and fate highly desirable. Accurate prediction of floc behaviour requires the quantification of 3-dimensional (3D) properties (size, shape and internal structure) that span several scales (i.e. nanometre [nm] to millimetre [mm]-scale). Traditional techniques (optical cameras and electron microscopy [EM]), however, can only provide 2-dimensional (2D) simplifications of 3D floc geometries. Additionally, the existence of a resolution gap between conventional optical microscopy (COM) and transmission EM (TEM) prevents an understanding of how floc nm-scale constituents and internal structure influence mm-scale floc properties. Here, we develop a novel correlative imaging workflow combining 3D X-ray micro-computed tomography (mu CT), 3D focused ion beam nanotomography (FIB-nt) and 2D scanning EM (SEM) and TEM (STEM) which allows us to stabilise, visualise and quantify the composition and multi-scale structure of sediment flocs for the first time. This new technique allowed the quantification of 3D floc geometries, the identification of individual floc components (e.g., clays, non-clay minerals and bacteria), and characterisation of particle-particle and structural associations across scales. This novel dataset demonstrates the truly complex structure of natural flocs at multiple scales. The integration of multi scale, state-of-the-art instrumentation/techniques offers the potential to generate fundamental new understanding of floc composition, structure and behaviour.

Within coastal and estuarine environments suspended cohesive sediments that are often closely associated with carbon, nutrients, pathogens and pollutants form aggregates commonly known as ‘flocs’. Understanding the settling dynamics and eventual fate of flocculated sediment is therefore a major issue for the management of aquatic environments. Several factors have been reported to influence the hydrodynamic behaviour of flocs, including size, shape, density and porosity. Recent evidence suggests that of these shape exerts the greatest influence on settling rates. Yet means of characterising shape have been limited to easy to measure quantities such as fractal dimension and circularity measured in 2-dimensions (2D) that fail to capture the highly complex, irregular geometries of sediment flocs. However, recent improvements in sampling methods, 3D imaging capabilities and data processing software enable for the first time the characterisation of flocs based on their 3D morphology. This study compares the morphologies of natural and artificial flocs generated under different environmental conditions. By employing a novel apparatus for the capture, immobilisation and handling of delicate floc samples, 3D X-ray micro-computed tomography (X-ray µCT) scans are successfully obtained and used to derive accurate volumetric reconstructions of tens of thousands of individual flocs. Using these datasets we compare different methods for describing shape, and test these for their ability to predict floc settling behaviours.

Within most environmental contexts, the collection of ‘undisturbed’ samples is widely relied upon in studies of soil and sediments. However, the impact of sampler-induced disturbance is rarely acknowledged, despite the potential significance of modification to sediment structure for the robustness of data interpretation. In this study, 3D computed X-ray microtomography (μCT) is used to evaluate and compare the disturbance imparted by four commonly used sediment sampling methods within a coastal salt marsh. Paired sediment core samples from a restored salt marsh at Orplands Farm, Essex, UK, were collected using four common sampling methods (push, cut, hammer and gouge methods). Sampling using two different area-ratio cores resulted in a total of 16 cores that were scanned with μCT to identify and evaluate sediment structural properties of samples that can be attributed to sampling method. 3D qualitative analysis identifies a suite of sampling disturbance structures including gross-scale changes to sediment integrity and substantial modification of pore space, structure and distribution, independent of sediment strength and stiffness. Quantitative assessment of changes to pore space and sediment density arising from the four sampling methods offers a means of direct comparison between the impact of depth sampling methods. Considerable disturbance to samples results from use of push, hammer and auguring samplers, whilst least disturbance is found in samples recovered by cutting and advanced trimming approaches. In many environmental studies involving sediment recovery through coring or other depth sampling, there is no such thing as an undisturbed sediment sample. The novel use of μCT scanning of sealed sediment cores has enabled the identification and evaluation of the nature and extent of sample disturbance resulting from four common types of sediment recovery methods. Depth sampling and coring methods remain key tools for understanding sediments and soils, but referring to undisturbed sediment sampling is no longer tenable without supporting evidence.

Coastal wetlands provide multiple ecosystem services through carbon storage, rich biodiversity and provision of harvested goods. A key service is their provision of ‘free’ coastal defence by dissipating storm wave and tidal energy, and their ability to accrete vertically and provide a natural buffer against the impact of projected sea-level rise. However, under IPCC climate projections, extreme hydrodynamic events associated with storm surges are expected to increase in both frequency and magnitude, exposing the margins of salt-marshes to increased erosion stress. The resistance of coastal wetlands to erosion during these events is poorly understood, and lateral erosion rates vary dramatically between UK salt-marshes. The NERC-RESIST project is exploring why this resilience to erosion varies, with a focus on the effect of the structural properties of the marsh substrate, to develop rapid evaluation tools of salt-marsh resistance for coastal engineers and inform future conservation efforts. The NERC-RESIST project explores how subsurface and surface structural characteristics of UK coastal wetlands affect their erodibility under tidal forcings, in order to provide coastal engineers with improved guidance for conservation schemes. In order to link internal sediment structure to erodibility, X-Ray CT scans were undertaken on large sediment cores recovered from two coastal wetlands (Tillingham, Essex; Warton, Lancashire) that are currently experiencing contrasting rates of lateral erosion. X-Ray CT scanning is a non-destructive imaging technique that allows a quantified analysis of 3D sediment properties, pore-space and root structure. After scanning, the cores were exposed to a variety of realistic wave energy conditions at the Grosser Wellen-Kanal (GWK) Large Flume Facility in Hannover, Germany, and high-resolution structure from motion imagery were collected to identify patterns of wave-induced erosion. This talk presents a 3D characterisation and detailed mapping of the topology of both pore and root networks within cores from the two salt-marshes. Two basic hypotheses are tested: the first examines the contribution of root systems in binding saltmarsh sediments and thus strengthening them against lateral erosion, and the second examines the role of macropores in facilitating the penetration of storm-wave water and energy into the sediment, contributing to weakening and increased erosion. A distance-mapping method is applied based on these hypotheses to develop a simple index of sediment structural vulnerability to erosion. These predictions are then compared to observed rates and patterns of storm wave-induced erosion from the GWK experiments. This informs an evaluation of the relative importance of inherent sediment properties (sediment type, cohesion, strength) and sediment structural characteristics in determining the erodibility of salt-marsh sediments.

The Brecon Beacons of central and southern Wales offer the opportunity to explore a range of geomorphological processes, particularly those relating to the rapid climate changes associated with the period subsequent to the Last Glacial Maximum. The mountains present some of the best preserved evidence in the British Isles of the interplay between glacial, periglacial and paraglacial processes, associated with conditions of marginal glaciation, and provide the most southerly evidence of Younger Dryas/Loch Lomond Stadial glaciation of Britain. The absence of evidence for landscape evolution in the region prior to the Last Glacial Maximum has recently begun to be addressed through insights derived from the subterranean geomorphology of limestone found in the south of the region. As one of the key sites of the early Industrial Revolution, the Brecon Beacons also preserve a unique landscape of anthropogenic (or even anthropocenic) geomorphology associated with large scale coal and iron extraction.

(1) Cambridge Coastal Research Unit, University of Cambridge, Cambridge, United Kingdom (bre24@cam.ac.uk), (2) Royal Netherlands Institure for Sea Research, Yerseke, Netherlands, (3) University of Cumbria, Carlisle, United Kingdom, (4) Queen Mary University Of London, London, United Kingdom, (5) University of Hamburg, Hambirg, Germany, (6) TU Braunschweig, Braunschweig, Germany, (7) British Geological Survey, Nottingham, United Kingdom, (8) University of Antwerp, Antwerp, Belgium, (9) Forschungszentrum Küste, Hannover, Germany

12 High resolution seismic data from the Dogger Bank in the central southern North Sea has revealed 13 that the Dogger Bank Formation records a complex history of sedimentation and 14 penecontemporaneous, large-scale, ice-marginal to proglacial glacitectonic deformation. These 15 processes led to the development of a large thrust-block moraine complex which is buried beneath a 16 thin sequence of Holocene sediments. This buried glacitectonic landsystem comprises a series of 17 elongate, arcuate moraine ridges (200 m up to > 15 km across; over 40-50 km long) separated by 18 low-lying ice marginal to proglacial sedimentary basins and/or meltwater channels, preserving the 19 shape of the margin of this former ice sheet. The moraines are composed of highly deformed (folded 20 and thrust) Dogger Bank Formation with the lower boundary of the deformed sequence (up to 40-50 21 m thick) being marked by a laterally extensive décollement. The ice-distal parts of the thrust 22 moraine complex are interpreted as a “forward” propagating imbricate thrust stack developed in 23 response to S/SE-directed ice-push. The more complex folding and thrusting within the more ice24 proximal parts of the thrust-block moraines record the accretion of thrust slices of highly deformed 25 sediment as the ice repeatedly reoccupied this ice marginal position. Consequently, the internal 26 structure of the Dogger Bank thrust-moraine complexes can be directly related to ice sheet 27 dynamics, recording the former positions of a highly dynamic, oscillating Weichselian ice sheet 28 margin as it retreated northwards at the end of the Last Glacial Maximum. 29