Impacts of land use changes and land management practices on upland catchment sediment dynamics: Pontbren, mid-Wales

There is growing concern that the adoption of intensive agricultural land management practices in upland areas of the UK over the past 50-60 years may have affected hydrological responses and sediment transfer regimes in river catchments and could, therefore, be contributing to increased levels of flood risk and ecological disturbance. However, recent evidence from a research catchment at Pontbren in mid-Wales indicates that the implementation of a more sustainable livestock farming strategy could help to mitigate some of these impacts, raising the possibility that strategic land use planning could be used as a cost-effective, multi-functional river management option. The impacts of historical land use changes and land management practices on contemporary sediment dynamics in the study area are explored in this thesis through a system approach which acknowledges the importance of interrelationships between hydrological and geomorphological processes. Results from hydrological experiments and modelling exercises are used to inform analyses of spatial and temporal variation in sediment production and transfer from a variety of potential sources. Grazed, agriculturally-improved pastures were found to supply fine material to stream channels via both surface runoff and field drains. In particular, drain-derived sediment is likely to represent an important component of the total fine sediment yield in subcatchments where agricultural intensification has been widespread. Agricultural drainage ditches were also found to act as sources of sediment in such areas, along with eroding channel banks. Sediment production from bank sources may relate to historical changes in peak flows caused by agricultural intensification. Stream sediment yields are strongly related to differences in sediment supply from the aforementioned sources and could therefore be reduced by limiting mobilisation at the point of origin within the landscape. In terms of channel-derived material, this could be achieved through peak flow reductions associated with woodland and hedgerow restoration

Impacts of land use changes and land management practices on upland catchment sediment dynamics: Pontbren, mid-Wales

There is growing concern that the adoption of intensive agricultural land management practices in upland areas of the UK over the past 50-60 years may have affected hydrological responses and sediment transfer regimes in river catchments and could, therefore, be contributing to increased levels of flood risk and ecological disturbance. However, recent evidence from a research catchment at Pontbren in mid-Wales indicates that the implementation of a more sustainable livestock farming strategy could help to mitigate some of these impacts, raising the possibility that strategic land use planning could be used as a cost-effective, multi-functional river management option. The impacts of historical land use changes and land management practices on contemporary sediment dynamics in the study area are explored in this thesis through a system approach which acknowledges the importance of interrelationships between hydrological and geomorphological processes. Results from hydrological experiments and modelling exercises are used to inform analyses of spatial and temporal variation in sediment production and transfer from a variety of potential sources. Grazed, agriculturally-improved pastures were found to supply fine material to stream channels via both surface runoff and field drains. In particular, drain-derived sediment is likely to represent an important component of the total fine sediment yield in subcatchments where agricultural intensification has been widespread. Agricultural drainage ditches were also found to act as sources of sediment in such areas, along with eroding channel banks. Sediment production from bank sources may relate to historical changes in peak flows caused by agricultural intensification. Stream sediment yields are strongly related to differences in sediment supply from the aforementioned sources and could therefore be reduced by limiting mobilisation at the point of origin within the landscape. In terms of channel-derived material, this could be achieved through peak flow reductions associated with woodland and hedgerow restoration

Re-introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation

Copyright © 2017 John Wiley & Sons, Ltd. Large wood is a powerful geomorphic agent in rivers, providing important habitat functions for a range of aquatic organisms, but has been subject to a long history of removal. Internationally, approaches to river restoration are increasingly incorporating large wood features, but generally favour simple flow deflectors (e.g. single logs, stripped of branches and anchored in place) over more complex structures that more accurately mimic natural wood jams. This paper explores channel response to wood-based restoration of an overwidened lowland chalk stream that incorporated whole felled trees. Hydraulics, sediment, topography and vegetation data were assessed for a 3year period for two restored reaches: an upstream reach where pre-restoration baseline data were obtained, and a downstream reach restored before data collection. Where pre-restoration data were available, the introduction of wood jams generated sediment deposition within jams leading to the development of vegetated marginal ‘benches’ and bed scour in adjacent areas of flow convergence. Patterns were less clear in the downstream reach, where restoration design was less ambitious and outcomes may have been affected by subsequent restoration work upstream. The results indicate that reintroduction of large wood (whole trees), can promote channel and habitat recovery from overwidening in lowland rivers, creating important ecological benefits through the provision of structurally complex marginal habitat and associated food resources. Longer-term assessments are required to establish whether the trajectories of change are persistent. The work emphasizes the effectiveness of restoration approaches that aim to ‘work with nature’. The ambitious design, incorporating structurally complex wood jams, was also low-cost, using materials available from the river corridor (existing riparian trees). Furthermore, ecosystem engineering effects were amplified by the colonization of wood jams by aquatic vegetation. The approach should, therefore, be transferable to other lowland rivers, subject to wider catchment constraints

Droplet Microfluidic Optimisation Using Micropipette Characterisation of Bio-Instructive Polymeric Surfactants

Droplet microfluidics can produce highly tailored microparticles whilst retaining monodispersity. However, these systems often require lengthy optimisation, commonly based on a trial-and-error approach, particularly when using bio-instructive, polymeric surfactants. Here, micropipette manipulation methods were used to optimise the concentration of bespoke polymeric surfactants to produce biodegradable (poly(d,l-lactic acid) (PDLLA)) microparticles with unique, bio-instructive surface chemistries. The effect of these three-dimensional surfactants on the interfacial tension of the system was analysed. It was determined that to provide adequate stabilisation, a low level (0.1% (w/v)) of poly(vinyl acetate-co-alcohol) (PVA) was required. Optimisation of the PVA concentration was informed by micropipette manipulation. As a result, successful, monodisperse particles were produced that maintained the desired bio-instructive surface chemistry

Alpha-particle-induced complex chromosome exchanges transmitted through extra-thymic lymphopoiesis in vitro show evidence of emerging genomic instability

Human exposure to high-linear energy transfer α-particles includes environmental (e.g. radon gas and its decay progeny), medical (e.g. radiopharmaceuticals) and occupational (nuclear industry) sources. The associated health risks of α-particle exposure for lung cancer are well documented however the risk estimates for leukaemia remain uncertain. To further our understanding of α-particle effects in target cells for leukaemogenesis and also to seek general markers of individual exposure to α-particles, this study assessed the transmission of chromosomal damage initially-induced in human haemopoietic stem and progenitor cells after exposure to high-LET α-particles. Cells surviving exposure were differentiated into mature T-cells by extra-thymic T-cell differentiation in vitro. Multiplex fluorescence in situ hybridisation (M-FISH) analysis of naïve T-cell populations showed the occurrence of stable (clonal) complex chromosome aberrations consistent with those that are characteristically induced in spherical cells by the traversal of a single α-particle track. Additionally, complex chromosome exchanges were observed in the progeny of irradiated mature T-cell populations. In addition to this, newly arising de novo chromosome aberrations were detected in cells which possessed clonal markers of α-particle exposure and also in cells which did not show any evidence of previous exposure, suggesting ongoing genomic instability in these populations. Our findings support the usefulness and reliability of employing complex chromosome exchanges as indicators of past or ongoing exposure to high-LET radiation and demonstrate the potential applicability to evaluate health risks associated with α-particle exposure.This work was supported by the Department of Health, UK. Contract RRX95 (RMA NSDTG)

The lifecycle of molecular clouds in nearby star-forming disc galaxies

It remains a major challenge to derive a theory of cloud-scale (⁠≲100 pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10−30Myr⁠, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities ΣH2≥8M⊙pc−2⁠, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at ΣH2≤8M⊙pc−2 GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75-90 per cent of the cloud lifetime), GMCs disperse within just 1−5Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4-10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H II regions are the fundamental units undergoing these lifecycles, with mean separations of 100−300pc in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.MC and JMDK gratefully acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through an Emmy Noether Research Group (grant number KR4801/1-1) and the DFG Sachbeihilfe (grant number KR4801/2-1). JMDK, APSH, SMRJ, and DTH gratefully acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). MC, JMDK, SMRJ, and DTH acknowledge support from the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD, grant number 57387355). APSH, SMRJ, and DTH are fellows of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD). BG gratefully acknowledges the support of the Australian Research Council as the recipient of a Future Fellowship (FT140101202). CNC, AH, and JP acknowledge funding from the Programme National ‘Physique et Chimie du Milieu Interstellaire’ (PCMI) of the Centre national de la recherche scientifique/Institut national des sciences de l’Univers (CNRS/INSU) with the Institut de Chimie/Institut de Physique (INC/INP), co-funded by the Commissariat a l’ ` energie ´ atomique et aux energies alternatives (CEA) and the Centre ´ national d’etudes spatiales (CNES). AH acknowledges support ´ by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with the INP and the Institut national de physique nucleaire et de physique des particules (IN2P3), co-funded by ´ CEA and CNES. PL, ES, CF, DL, and TS acknowledge funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 694343). The work of AKL, JS, and DU is partially supported by the National Science Foundation (NSF) under Grants No. 1615105, 1615109, and 1653300. AKL also acknowledges partial support from the National Aeronautics and Space Administration (NASA) Astrophysics Data Analysis Program (ADAP) grants NNX16AF48G and NNX17AF39G. ER acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference number RGPIN-2017-03987. FB acknowledges funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 726384). GB is supported by the Fondo de Fomento al Desarrollo Cient´ıfico y Tecnologico of the Comisi ´ on Nacional de ´ Investigacion Cient ´ ´ıfica y Tecnologica (CONICYT/FONDECYT), ´ Programa de Iniciacion, Folio 11150220. SCOG acknowledges ´ support from the DFG via SFB 881 ‘The Milky Way System’ (subprojects B1, B2, and B8) and also via Germany’s Excellence Strategy EXC-2181/1–390900948 (the Heidelberg STRUCTURES Excellence Cluster). KK gratefully acknowledges funding from the DFG in the form of an Emmy Noether Research Group (grant number KR4598/2-1, PI Kreckel). AU acknowledges support from the Spanish funding grants AYA2016-79006-P (MINECO/FEDER) and PGC2018-094671-B-I00 (MCIU/AEI/FEDER)

The lifecycle of molecular clouds in nearby star-forming disc galaxies

It remains a major challenge to derive a theory of cloud-scale (⁠≲100 pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10−30 Myr⁠, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities Σ_(H₂) ≥ 8 M_⊙ pc⁻²⁠, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at Σ_(H₂) ≤ 8 M_⊙ pc⁻² GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just 1−5 Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4–10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H II regions are the fundamental units undergoing these lifecycles, with mean separations of 100−300 pc in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles

Does Lack of Multinutrient Supplementation During Early Pregnancy Increase Vulnerability to Alcohol-Related Preterm or Small-for-Gestational-Age Births?

The objective of this study was to assess whether women who do not take multinutrient supplements during early pregnancy are more susceptible to the effects of low-to-moderate alcohol consumption on preterm birth and small-for-gestational-age birth (SGA) compared to women who do take multinutrients. This analysis included 800 singleton live births to mothers from a cohort of pregnant women recruited for a population-based cohort study conducted in the Kaiser Permanente Medical Care Program in Northern California. Participants were recruited in their first trimester of pregnancy and information about their alcohol use and supplement intake during pregnancy was collected. Preterm birth (n = 53, 7%) was defined as a delivery prior to 37 completed weeks of gestation and SGA birth (n = 124, 16%) was defined as birth weight less than the 10th percentile for the infant’s gestational age and sex compared to US singleton live births. A twofold increase in the odds of SGA birth attributed to low-to-moderate alcohol intake was found among multinutrient supplement non-users (95% CI: 1.1, 5.3). Yet, among multinutrient supplement users, there was no increased risk of an SGA birth for women who drank low-to-moderately compared to women who abstained (aOR: 0.97, 95% CI: 0.6, 1.6). Similar results emerged for preterm birth. Our findings provide marginal evidence that multinutrient supplementation during early pregnancy may modify the risk of SGA births and preterm birth associated with alcohol consumption during pregnancy and may have important implications for pregnant women and women of child-bearing age. However, future research needs to be conducted

An uncertainty principle for star formation - II. A new method for characterising the cloud-scale physics of star formation and feedback across cosmic history

The cloud-scale physics of star formation and feedback represent the main uncertainty in galaxy formation studies. Progress is hampered by the limited empirical constraints outside the restricted environment of the Local Group. In particular, the poorly-quantified time evolution of the molecular cloud lifecycle, star formation, and feedback obstructs robust predictions on the scales smaller than the disc scale height that are resolved in modern galaxy formation simulations. We present a new statistical method to derive the evolutionary timeline of molecular clouds and star-forming regions. By quantifying the excess or deficit of the gas-to-stellar flux ratio around peaks of gas or star formation tracer emission, we directly measure the relative rarity of these peaks, which allows us to derive their lifetimes. We present a step-by-step, quantitative description of the method and demonstrate its practical application. The method's accuracy is tested in nearly 300 experiments using simulated galaxy maps, showing that it is capable of constraining the molecular cloud lifetime and feedback time-scale to $<0.1$ dex precision. Access to the evolutionary timeline provides a variety of additional physical quantities, such as the cloud-scale star formation efficiency, the feedback outflow velocity, the mass loading factor, and the feedback energy or momentum coupling efficiencies to the ambient medium. We show that the results are robust for a wide variety of gas and star formation tracers, spatial resolutions, galaxy inclinations, and galaxy sizes. Finally, we demonstrate that our method can be applied out to high redshift ($z\lesssim4$) with a feasible time investment on current large-scale observatories. This is a major shift from previous studies that constrained the physics of star formation and feedback in the immediate vicinity of the Sun