Headwater streams drain the majority of the landscape, yet little is known about their form and function in comparison to lowland rivers. Better understanding of their morphology and sediment transport processes will improve understanding of landscape evolution and promote a more complete view of fluvial systems. Therefore, the goal of my project was to determine controls on headwater channel form and function in the humid, moderate-relief drainage basins of the Valley and Ridge and Blue Ridge provinces in the southern Appalachian Mountains. I surveyed nine headwater (0.33 - 2 km2 drainage area) streams in a variety of bedrock, climate, base level, and land use conditions and produced a high-resolution dataset on their longitudinal and cross sectional form. This data was analyzed empirically to determine controls on channel form, and used in hydrologic modeling to determine the ability of the channels to erode their beds during regularly recurring flows as well as the recurrence interval of bankfull flows. Field survey results demonstrate that the channels are dominantly alluvial and vary greatly between and within channels in their overall longitudinal form, channel slope values, and grain size. These variations are due to differences in bedrock resistance at the formation level as well as at short wavelengths. Bedrock also controls channel form through its influence on local and regional base level, channel initiation processes, and log jam abundance. Hydraulic geometry, steam competence and bankfull flow recurrence also vary greatly between and within channels. This variation is due to the high sensitivity of the streams to hillslope influences such as bedrock resistance, boulder influx, and soil profile development. Increases in bedrock resistance within a channel create knickpoints that lower stream competence and slow hilllslope erosion. Stream competence is generally higher in channels with erodable bedrock and lower in channels with resistant bedrock, but most channels could entrain the majority of the grains on their bed at 2-year stormflows. Bankfull is a larger, less frequent flow than the 2-year storm at very small drainage areas (<0.4 km2), but is approximately a 2-year recurrence flow at larger drainage areas. Bankfull occurs less frequently in North Carolina Blue Ridge streams, due to deep soils that form on metamorphic bedrock under an more intense precipitation regime and have high rainfall storage capacity. Results indicate that variability is a fundamental feature of headwater streams and that they do not follow channel slope, hydraulic geometry, and bankfull relations developed in lowland river systems. / Master of Science

Erosion of a river bed has important implications with respect to scour around river structures such as bridges, transport of contaminants attached to the sediment, and disruption or destruction of aquatic habitats. Erosion occurs when the resistive strength of the sediment is overcome by the hydrodynamic forces produced by the flow of water. This resistance to erosion in a sediment originates from gravity or interparticle forces for coarse sediment (sand and gravel) and fine sediment (silt and clay), respectively. Since the erosion of fine sediment depends on the combination of many interparticle forces, and this combination fluctuates widely amongst different fine sediments, past studies have had difficulty finding a consistent method to estimate fine sediment erosion. This study analyzes sediments that fall in the transition size range between fine and coarse sediments and compares the findings with those from fine sediments (Wang 2013) and sandy coarse sediments (Navarro 2004, Hobson 2008), in order to correlate the erosion rates of both sediment types to their physical characteristics. In this study, kaolin-sand mixtures were prepared by mixing various percentages of Georgia kaolin by weight ranging from 30% to 100% with industrial fine sand and tap water. Geotechnical and other tests of sediment properties were performed to measure water content, bulk density, grain size distribution, temperature, pH, and conductivity of these mixtures. Hydraulic flume experiments measured the erosion rates of each sediment and these rates were used to estimate the critical shear stress correlating to that mixture. Relationships between the physical properties of the sediment and critical shear stress were developed by multiple regression analysis. An alternative option of estimating the critical shear stress by a weighted equation, which uses the combination of fine sediment erosion and coarse sediment erosion equations separately, was explored and found to be a viable and accurate option to estimating both coarse and fine sediment erosion from the same parameters and equation. The results from this study can be used to estimate sediment erodibility and thus river bed stability based on simple tests of physical properties of the river bed sediment and will help predict scour around bridges and other flow obstructions.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Sediment delivery to a basin exerts a first-order control over sedimentation, and therefore study of sedimentary rocks can reveal information about the nature of sediment delivery in the past. This dissertation examines several aspects of this problem using experimental, outcrop, and subsurface data. Flume experiments were undertaken to test the combined effects of autogenic alluvial aggradation and forced regression on the development of fluviodeltaic stratigraphy. Alluvial aggradation occurred in response to steady relative sea-level fall, and eventually consumed the entire sediment budget as the river lengthened in response to forced regression. The Campanian Lower Castlegate Sandstone (Utah) was studied as a potential ancient analog resulting from similar autogenic behaviors as observed in the experiments. Extensive measurement of grain-size distributions and paleo-flow depths from outcrop were utilized to explore downstream changes in paleo-hydraulics of the ancient fluvial systems in the Lower Castlegate in response to extensive alluvial aggradation and consequent loss of sediment from transport. An interesting finding was the stratigraphic signature of backwater hydraulic conditions in the distal reaches of the Lower Castlegate paleo-rivers. Finally, a simple and novel inversion scheme was developed for estimating paleo-sediment flux from ancient shelf-margin successions. An advantage of the methodology is that it allows for both spatial and temporal reconstruction of paleo-sediment flux patterns. The inversion scheme was applied to shelf-margin successions in the Washakie-Sand Wash Basin of Wyoming, the New Jersey Atlantic margin, the North Slope of Alaska, and the Zambezi margin of East Africa using published subsurface datasets. The Neogene passive margins within the studied datasets were found to consistently deposit around one-third of their total sediment budget on the shelf-margin topset, and bypass two-thirds of their budget beyond the shelf edge. The implications of this finding on the flux of terrestrial-derived particulate organic carbon (POC) from rivers to the ocean were explored, and a long-term average flux of POC to deepwater storage was estimated. The sediment-flux inversion scheme was also applied to derive input parameters for stratigraphic modeling of the Ebro margin. The modeling results indicate that the autostratigraphic behavior of the margin may have been previously underestimated. / text

This study proposes the use of a pipe line system to transport the inflow sediment to a reservoir through the dam, and discharge it downstream. The system is powered by the available head at the dam. It aims at restoring the original sediment transport regime of the river (i.e. before the dam was built). The idea is fundamentally sound because of the much more efficient sediment transport characteristics of pipes compared to that of open channels. The necessary theory for the hydraulic design of such a system was simply not available and is developed in this study. The work of numerous previous investigators is summarized in the final results and in the developed equation which allows for the calculation of the capacity transport concentration of sediments in pipes. This equation, coupled with the most accepted head loss equation, and the continuity principle, allows for the hydraulic design of systems transporting grannular material. The calculation procedures were fitted into computer programs. In addition to computer programs, design charts where developed which allow for quick application as well as visualization of the developed concepts. It was concluded that the proposed system is fundamentally feasible. Although no economic analysis was conducted, indicators show that it is also economically favorable.

SUMMARY: This thesis is focused on identification of spatial distribution of Pb, Zn and Cu pollution in floodplain sediments of the Litavka River and reconstruction of its pollution history related to mining and metallurgy of Ag, Pb and Zn in the Příbram area. Sampling was performed in floodplain and sediments were analysed by X-ray fluorescence spectroscopy (ED XRF) in aim to understand the distribution of the target elements in the floodplain fill. The results of ED XRF were calibrated by analyses of selected sediment samples by inductively coupled plasma mass spectrometry with (ICP- MS). The same method was used to determine ratios of lead stable isotopes 206 Pb and 207 Pb. Additionally, magnetic susceptibility was measured, granulometric analysis of selected samples was performed, and cation-exchange capacity (CEC) was determined. The aim of the work was to attempt to reconstruct history of pollution of the floodplain sediments. Sediment dating was performed by 14 C, 137 Cs and 210 Pb. Key words: aluvial sediment, contamination, heavy metals, reconstruction

by Tse Sui-fai, Peter. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 161-169). / ABSTRACT --- p.ii / ACKNOWLEDGEMENT --- p.iv / TABLE OF CONTENTS --- p.vi / LIST OF TABLES --- p.ix / LIST OF FIGURES --- p.x / LIST OF PLATES --- p.xi / Chapter CHAPTER I --- INTRODUCTION / Chapter 1.1 --- Scope of the problem --- p.1 / Chapter 1.2 --- Occurrence of urban sediments in an urban setting --- p.6 / Chapter 1.3 --- Nature of urban sediments --- p.9 / Chapter 1.4 --- Importance of studying urban sediment --- p.9 / Chapter 1.5 --- Objectives of this research --- p.10 / Chapter 1.6 --- Structure of this research --- p.10 / Chapter CHAPTER II --- LITERATURE REVIEW / Chapter 2.1 --- Hydrological problems related to urbanisation --- p.13 / Chapter 2.2 --- Importance of the urban sediment on the environment --- p.15 / Chapter 2.2.1 --- Road surface sediments --- p.20 / Chapter 2.2.2 --- Gully pot or catchment sediments --- p.22 / Chapter 2.2.3 --- Sewer sediments --- p.24 / Chapter 2.3 --- Studies on the characteristics of urban sediments --- p.25 / Chapter 2.3.1 --- Particle size and volatile content --- p.26 / Chapter 2.3.2 --- Surface features identification by using the SEM --- p.27 / Chapter 2.3.3 --- Studies in sub-tropical humid areas --- p.28 / Chapter 2.4 --- Problems raised from the previous studies and directions --- p.29 / Chapter CHAPTER III --- STUDY AREA - FO TAN CATCHMENT / Chapter 3.1 --- Introduction --- p.31 / Chapter 3.1.1 --- Hong Kong --- p.32 / Chapter 3.2 --- Fo Tan Catchment --- p.38 / Chapter 3.2.1 --- Geology --- p.44 / Chapter 3.2.2 --- Landuse --- p.48 / Chapter 3.2.3 --- Road surface and traffic characteristics --- p.49 / Chapter 3.2.4 --- Stormwater drainage network --- p.54 / Chapter 3.2.5 --- A unique hydrological year --- p.55 / Chapter 3.3 --- Conclusion --- p.59 / Chapter CHAPTER IV --- METHODOLOGY / Chapter 4.1 --- Rationale for the research method --- p.60 / Chapter 4.1.1 --- Introduction --- p.60 / Chapter 4.1.2 --- Operationalisation of the concept --- p.62 / Chapter 4.1.2.1 --- Street surface sediments --- p.62 / Chapter 4.1.2.2 --- Gully pot sediments --- p.63 / Chapter 4.1.2.3 --- Sewer sediments --- p.63 / Chapter 4.1.2.4 --- Channel deposits --- p.64 / Chapter 4.1.3 --- Study area---Fo Tan --- p.64 / Chapter 4.2 --- Empirical data and their collection --- p.64 / Chapter 4.2.1 --- Sampling sites --- p.64 / Chapter 4.2.2 --- Sample collection --- p.65 / Chapter 4.2.2.1 --- Street surface sediments --- p.66 / Chapter 4.2.2.2 --- Gully pot sediments --- p.66 / Chapter 4.2.2.3 --- Channel deposits --- p.67 / Chapter 4.2.3 --- Sample treatment --- p.67 / Chapter 4.3 --- Analyses of samples --- p.68 / Chapter 4.3.1 --- Particle size distribution --- p.68 / Chapter 4.3.1.1 --- Dry sieving analysis --- p.69 / Chapter 4.3.2 --- Volatile solids --- p.69 / Chapter 4.3.3 --- Surface characteristics of sediment grains --- p.70 / Chapter 4.3.3.1 --- The use of scanning electron microscope (SEM) --- p.70 / Chapter 4.3.3.2 --- Preparation of samples --- p.71 / Chapter 4.3.4 --- Data analysis and presentation --- p.73 / Chapter 4.4 --- Conclusion --- p.74 / Chapter CHAPTER V --- PHYSICAL CHARACTERISTICS OF URBAN SEDIMENTS / Chapter 5.1 --- Introduction --- p.75 / Chapter 5.2 --- Results --- p.76 / Chapter 5.2.1 --- Composition of the street surface sediments --- p.76 / Chapter 5.2.2 --- Street surface sediment loading --- p.79 / Chapter 5.2.3 --- Loading rate with slope factor --- p.86 / Chapter 5.2.4 --- Street sediment loads in different landuse areas --- p.86 / Chapter 5.2.5 --- Particle size distribution of the sediments --- p.88 / Chapter 5.2.5.1 --- Particle sizing for different sites in the same environment --- p.88 / Chapter 5.2.5.2 --- Particle size distribution for different sampling dates --- p.89 / Chapter 5.2.5.3 --- Particle size distribution in different environments --- p.89 / Chapter 5.2.5.5 --- Phi study --- p.91 / Chapter 5.2.6 --- Bivariate scattergram analysis --- p.96 / Chapter 5.3 --- Discussion --- p.100 / Chapter CHAPTER VI --- VOLATILE SOLIDS ANALYSIS / Chapter 6.1 --- Introduction --- p.105 / Chapter 6.2 --- Results --- p.108 / Chapter 6.2.1 --- The mean volatile solids in different environments --- p.108 / Chapter 6.2.2 --- The relationship between phi median and volatile solids content --- p.109 / Chapter 6.2.3 --- Particle size distribution on the volatile solids content --- p.110 / Chapter 6.3 --- Discussion --- p.111 / Chapter 6.3.1 --- Effects of road surface characteristics --- p.111 / Chapter 6.3.2 --- Effects of traffic flow --- p.112 / Chapter 6.3.3 --- Effects of landuse pattern --- p.114 / Chapter 6.4 --- Particle size and volatile solids: a synthesis --- p.114 / Chapter 6.5 --- Conclusion --- p.119 / Chapter CHAPTER VII --- SCANNING ELECTRON MICROSCOPIC STUDY / Chapter 7.1 --- Introduction --- p.120 / Chapter 7.2 --- Results --- p.125 / Chapter 7.2.1 --- Quantitative analysis of the surface features on grains from different depositional environments --- p.125 / Chapter 7.2.2 --- Description of the texture of the samples --- p.130 / Chapter 7.2.3 --- Texture interpretation --- p.142 / Chapter 7.3 --- Discussions --- p.143 / Chapter 7.3.1 --- Surface texture description and its relationship to landuse pattern --- p.143 / Chapter 7.3.2 --- Sediment transport in an urban setting: a synthesis --- p.146 / Chapter CHAPTER VIII --- CONCLUSION / Chapter 8.1 --- Findings of this research --- p.152 / Chapter 8.2 --- Future directions --- p.157 / Chapter 8.2.1 --- Equipment used in reducing urban sediments --- p.157 / Chapter 8.2.2 --- Sweeping practices of the street surface --- p.158 / Chapter 8.2.3 --- The use of SEM in urban sediments --- p.159 / Chapter 8.3 --- Conclusions --- p.160 / REFERENCES --- p.161 / APPENDICES --- p.170

by Wan Yuk-ching. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 146-152). / Abstracts in English and Chinese. / List of Tables --- p.i / List of Figures --- p.iii / List of Plates --- p.v / Chapter CHAPTER I --- INTRODUCTION / Chapter 1.1 --- Scope of the Problem --- p.1 / Chapter 1.2 --- Importance of the Urban Sediments on the Environment --- p.8 / Chapter 1.3 --- Hydrological and Sedimentological Problems Related to Urbanization -a Storm Event Basis --- p.13 / Chapter 1.4 --- Studies in Sub-tropical Humid Areas --- p.17 / Chapter 1.5 --- Objectives of this Research --- p.18 / Chapter CHAPTER II --- CHARACTERISTICS OF URBAN SEDIMENTS / Chapter 2.1 --- Sediments Transportation Pattern of Storm Events --- p.19 / Chapter 2.2 --- Particle Size Parameter --- p.29 / Chapter 2.3 --- Volatile and Chemical Parameters of Total Sediment Loading --- p.33 / Chapter 2.4 --- Problems Arisen from the Review of Previous Studies and Directions --- p.36 / Chapter CHAPTER III --- METHODOLOGY / Chapter 3.1 --- Experimental Design --- p.37 / Chapter 3.1.1 --- Catchment Approach --- p.38 / Chapter 3.1.2 --- Storm base Approach --- p.39 / Chapter 3.2 --- Study Area --- p.41 / Chapter 3.2.1 --- Rainfall Pattern --- p.41 / Chapter 3.3 --- Nature of the Study Areas --- p.44 / Chapter 3.3.1 --- Location --- p.45 / Chapter 3.3.2 --- Relief and Geology --- p.47 / Chapter 3.3.3 --- Landuse Pattern --- p.49 / Chapter 3.3.4 --- Climatic Condition --- p.57 / Chapter 3.3.5 --- Streamflow Measurement --- p.59 / Chapter 3.4 --- Suspended Sediment Concentration --- p.61 / Chapter 3.4.1 --- Sample Collection --- p.61 / Chapter 3.4.2 --- Laboratory Procedures --- p.62 / Chapter 3.4.3 --- Instantaneous Sediment Concentration --- p.63 / Chapter 3.5 --- Volatile and Mineral Solids --- p.63 / Chapter 3.6 --- Particle Size Measurement --- p.65 / Chapter CHAPTER IV --- TRANSPORTATION PATTERN OF STORM SEDIMENTS IN URBAN CATCHMENTS / Chapter 4.1 --- Introduction --- p.66 / Chapter 4.2 --- Suspended Sediment Transport Patterns During Storm Events --- p.70 / Chapter 4.3 --- The Relationship Between Discharge and Instantaneous Sediment Concentration --- p.81 / Chapter 4.4 --- Additional Factors Affecting Instantaneous Sediment Concentrations During Storm Events --- p.87 / Chapter 4.4.1 --- University Campus --- p.88 / Chapter 4.4.2 --- Fo Tan --- p.91 / Chapter 4.5 --- Discussion --- p.93 / Chapter CHAPTER V --- SEDIMENT CHARACTERISTICS / Chapter 5.1 --- Introduction --- p.97 / Chapter 5.2 --- Characterization of Sediments --- p.98 / Chapter 5.3 --- Variations in Sediment Size --- p.101 / Chapter 5.3.1 --- Between-Storm Variations in Particle Size --- p.103 / Chapter 5.3.1.1 --- Size Distribution Curves --- p.103 / Chapter 5.3.1.2 --- Median Particle Size --- p.107 / Chapter 5.3.2 --- Within-Storm Variations in Particle Size --- p.108 / Chapter 5.3.3 --- Factors Affecting the Between Storm Variations in Sediment Particle Size --- p.120 / Chapter 5.4 --- Variations in the Sediment Volatile Content --- p.123 / Chapter 5.4.1 --- Differences in Sediment Volatile Content Between the Two Catchments --- p.123 / Chapter 5.4.2 --- Variations in Volatile Content Between and Within Storms --- p.124 / Chapter 5.4.3 --- Timing of the Volatile Content Peaks --- p.128 / Chapter 5.4.4 --- Factors Affecting the Volatile Content --- p.131 / Chapter 5.4.5 --- Some General Observations on Sediment Volatile Content --- p.133 / Chapter 5.5 --- Summary and Discussion --- p.133 / Chapter CHAPTER VI --- CONCLUSION / Chapter 6.1 --- Summary of Findings --- p.137 / Chapter 6.2 --- Implications of the Research Findings --- p.141 / Chapter 6.3 --- Limitations of this Study and Suggestions for Future Work --- p.143

Mudanças na taxa de acumulação e na natureza da matéria orgânica sedimentar, e suas relações com as variações climáticas e flutuações do nível relativo do mar durante os últimos 8.500 anos cal. A.P. foram investigadas em dois testemunhos provenientes do Saco de Ribeira, Enseada do Flamengo, e junto à praia do Lázaro, Enseada da Fortaleza, na região de Ubatuba, litoral norte do Estado de São Paulo. Para o estudo as amostras coletadas foram submetidas a diversas análises - granulometria, teor de CaCO3, teores de Carbono orgânico, Nitrogênio e Enxofre totais, e razões isotópicas de carbono. Datações 14C, calibradas para a idade calendário, permitiram estabelecer um modelo de idades para as variações sedimentares detectadas. Intervalos de clima mais quente, 8.000-6.000 anos cal. A.P., foram acompanhados de um aumento na taxa de acumulação de carbono T.A.C. (10-13 g m-2 ano-1), seguida de diminuição após 5.000 anos cal. A.P., para valores inferiores a 2 g m-2 ano-1. Variações climáticas regionais, possivelmente relacionadas a chuvas torrenciais, próximos ao máximo transgressivo, de 5.100 anos 14C A.P., foram detectadas pelo aumento nos valores de T.A.C. (10-12 g. m- 2 ano-1), aumento nas taxas de acumulação de massa (T.A.M.) e deposição de sedimentos mais grossos, acompanhados de aumento na tendência continental da natureza da matéria orgânica. As maiores tendências continentais da matéria orgânica sedimentar, registradas aproximadamente entre 1.500-1.200 anos cal. A.P., podem ser decorrentes de uma oscilação negativa do nível do mar. No geral, todos os resultados estão de acordo com as curvas de variação do nível relativo do mar, já descritas na literatura. As análises sedimentares da região estudada revelaram um evento regressivo-trangressivo, que ainda não havia sido referido para o Estado de São Paulo. A partir de ~2.000 anos cal. A.P., o mar teria atingido um nível mais baixo que o atual, com o mínimo provavelmente entre 1.500-1.200 anos cal. A.P., e encontra-se em ascensão até os dias atuais. As características anóxicas e a matéria orgânica sedimentar de origem planctônica registradas junto à praia do Lázaro, em meio a condições de energia relativamente mais alta, em ~900 anos cal. A.P., foram consideradas como resultado de condições óxicas das águas, acompanhadas de altas taxas de produtividade, e subseqüente degradação da matéria orgânica, existentes no período anterior. / Changes in the organic carbon accumulation rates (Corg A.R.) and organic matter source characteristics and their relation to climate and relative sea level changes during the last 8.500 cal. yr. B.P. were investigated in two sediment cores from 2 embayments - Flamengo and Fortaleza inlets - northern coast of São Paulo State. Sediment samples were analysed for grain size, organic Carbon, total Nitrogen and Sulphur contents, and ?13C ratio. Radiocarbon datings provided a model age to the sedimentary deposits. The warm climate interval 8.000-6.000 cal. yr. B.P. was accompanied by an increase in the Corg A.R. (10-13 g.m.-2 yr -1) and a decrease (~2 g.m.-2 yr -1) in the last ~5.000 cal. yr. B.P. Regional climate changes, as stormy weather, that may have ocurred near the maximum transgressive period called Santos Transgression at 5.100 yr. B.P., were recorded in the sedimentary profiles by relatively hight T.A.C. and T.A.M. values, coaser grain size sediment delivery, and enhanced terrestrial organic matter source characteristics. Improvement of terrestrial origin of the sedimentary organic matter recorded between 1.500-1.200 cal. yr. B.P in the studied area was mainly related to a negative sea-level oscillation. All the results are in general agreement with the existing sea level change curves. The sedimentary profiles suggest a negative sea-level fall event, that had\'nt been described yet for São Paulo State. It\'s proposed that the negative oscillation would have begun at ~2.000 cal. yr. B.P.and reached a minimum probably between 1.500-1200 cal. yr. B.P. The relative sea level has been rising since then. Anoxic conditions accompanied by algal origins of sedimentary organic matter, observed in the sedimentary profile from Fortaleza inlet at 900 cal. yr. B.P, during a more oxidizing environment are considered as a result of a previous well oxygencontaining water column and high productivity rates.

Parrotfish are a diverse and ubiquitous group found on coral reefs worldwide. They are categorised into three main feeding modes; the browsers, scrapers and excavators, which together perform a number of important functional roles on coral reefs. Scraper and excavator parrotfish are common on most Indo-Pacific coral reefs where their roles in bioerosion, sediment production, grazing pressure and sediment reworking have been shown to influence benthic community composition, reef growth potential and sediment supply to reef habitats and reef associated sedimentary landforms. However, despite the widely known importance of parrotfish on coral reefs, our understanding of how their roles in carbonate cycling vary among species and among whole parrotfish communities in different reef habitats remains limited. This thesis produces original contributions to knowledge in the areas of species specific bioerosion estimates for the central Indian Ocean, bottom-up controls of habitat type on parrotfish assemblages and how variations in parrotfish assemblages translate to contributions to carbonate cycling processes among different reef habitats. The study was carried out across eight habitats on an atoll-edge reef platform in the central Maldives, where it was found that parrotfish community composition was driven by reef structural complexity and substrate type. Parrotfish occurred in six of the eight habitats, comprising ~44% of the platform area. Among these habitats, overall grazing pressure, bioerosion rates, sediment reworking and sediment production varied markedly. These processes were also found to have different spatial patterns over the reef platform, showing that they are not necessarily tightly coupled. In addition, reef habitats can vary in their importance for both sediment supply, and the relative importance of reworked sediment. Parrotfish produced a wide range of sediment size fractions, from < 32 to 2000 μm and produced predominantly coral sands (>80%) between 125 and 1000 μm in diameter. This is comparable to the grain types found on local reef islands, and it is likely that the most significant supply of this material is from habitats on the atoll-edge side of the platform (which make up ~20% of the total platform area). Quantifying parrotfish functional roles and understanding the drivers behind these processes is important for informing future empirical and modelling studies, particularly as coral reefs undergo a time of dramatic environmental change.