O objetivo desta tese foi avaliar os impactos decorrentes das mudanças de uso da terra e da variabilidade climática nos recursos hídricos (vazão e fluxo de sedimentos), em mesoescala (bacia do rio Piracicaba) e em pequena escala (microbacia do Ribeirão das Posses), através de um estudo de modelagem numérica com o modelo SWAT (Soil and Water Assessment Tool). Foram utilizados dados de modelo numérico de terreno, mapas de solo e uso da terra, temperatura, precipitação, vento, radiação solar e umidade relativa para forçar o modelo SWAT. O modelo mostrou resultados satisfatórios de desempenho na comparação com dados observados, conforme mostram os índices estatísticos na bacia do rio Piracicaba (COE entre 0,97 e 0,99 para vazão e de 0,90 para fluxo de sedimentos) e no Ribeirão das Posses (COE de 0,53 para a vazão e 0,7 para fluxo de sedimentos). Nas simulações de modificações de uso da terra os resultados indicam que em ambas as bacias as maiores vazões ocorrem nos cenários de desflorestamento, sendo o cenário de pastagem o de valores mais expressivos. O modelo correspondeu às evidências de que as vazões máximas, por exemplo os eventos de inundações, podem ser mitigados com o reflorestamento e que o cenário de antropização com gramíneas, no caso das pastagens e cana-de-açúcar, os eventos extremos tendem a ser aumentados ainda mais. Na avaliação da simulação dos fluxos de sedimentos, o cenário de reflorestamento por eucalipto mostra redução na perda do solo, porém ainda abaixo do cenário de reflorestamento por vegetação nativa, que apresentou os menores valores de fluxo de sedimentos, em ambas as bacias. Na simulação levando-se em consideração as mudanças climáticas, os resultados mostram aumento de vazão para o futuro (2078-2098) e consequente aumento de fluxo de sedimento, sendo um aumento médio de 12 % nas vazões do Piracicaba e de 19 % no fluxo de sedimentos. No Ribeirão das Posses este padrão de resposta também ocorreu, com aumento de 46% na vazão e 40 % no fluxo de sedimentos. / The aim of this thesis was to evaluate the impacts of changes in land use and climate variability on water resources (discharge and sediment fluxes), into mesoscale (Piracicaba River basin) and small-scale (watershed Ribeirão das Posses) processes throughout a study of numerical modeling with SWAT model (Soil and Water Assessment Tool). Data of numerical model of terrain, soil maps and land use, temperature, precipitation, wind speed, solar radiation and relative humidity forced the SWAT model. The model showed a satisfactory performance in comparison with the observed data, as showed by the statistical indices of the Piracicaba River Basin (COE between 0.97 and 0.99 to 0.90 for flow and sediment fluxes) and Ribeirão das Posses (COE of 0.53 to 0.7 for flow and sediment fluxes). In simulations of changes in land use the results indicate that in both basins larger flows occur in the case of deforestation scenarios, being the scene of the pasture the highest values. The model corresponded to the evidence that peak flows, for example the events of flooding can be mitigated with reforestation and the scenario of anthropogenic with grasses for grazing land and sugar cane, extreme events tend to be further enhanced too. In assessing the simulation of sediment flows, the scenario of reforestation with eucalyptus shows reduction in soil loss, but still below the scenario reforestation with native vegetation, which presented the lowest values of sediment flux in both basins. In the simulation taking into account climate change, the results show increased flow to the future (2078-2098) and consequent increase in stream sediment, with an average 12% increase in the flows of Piracicaba and 19 % in the flow sediment. In Ribeirão das Posses this response pattern also occurred with a 46% increase in throughput and 40 % in the stream sediments.

O objetivo desta tese foi avaliar os impactos decorrentes das mudanças de uso da terra e da variabilidade climática nos recursos hídricos (vazão e fluxo de sedimentos), em mesoescala (bacia do rio Piracicaba) e em pequena escala (microbacia do Ribeirão das Posses), através de um estudo de modelagem numérica com o modelo SWAT (Soil and Water Assessment Tool). Foram utilizados dados de modelo numérico de terreno, mapas de solo e uso da terra, temperatura, precipitação, vento, radiação solar e umidade relativa para forçar o modelo SWAT. O modelo mostrou resultados satisfatórios de desempenho na comparação com dados observados, conforme mostram os índices estatísticos na bacia do rio Piracicaba (COE entre 0,97 e 0,99 para vazão e de 0,90 para fluxo de sedimentos) e no Ribeirão das Posses (COE de 0,53 para a vazão e 0,7 para fluxo de sedimentos). Nas simulações de modificações de uso da terra os resultados indicam que em ambas as bacias as maiores vazões ocorrem nos cenários de desflorestamento, sendo o cenário de pastagem o de valores mais expressivos. O modelo correspondeu às evidências de que as vazões máximas, por exemplo os eventos de inundações, podem ser mitigados com o reflorestamento e que o cenário de antropização com gramíneas, no caso das pastagens e cana-de-açúcar, os eventos extremos tendem a ser aumentados ainda mais. Na avaliação da simulação dos fluxos de sedimentos, o cenário de reflorestamento por eucalipto mostra redução na perda do solo, porém ainda abaixo do cenário de reflorestamento por vegetação nativa, que apresentou os menores valores de fluxo de sedimentos, em ambas as bacias. Na simulação levando-se em consideração as mudanças climáticas, os resultados mostram aumento de vazão para o futuro (2078-2098) e consequente aumento de fluxo de sedimento, sendo um aumento médio de 12 % nas vazões do Piracicaba e de 19 % no fluxo de sedimentos. No Ribeirão das Posses este padrão de resposta também ocorreu, com aumento de 46% na vazão e 40 % no fluxo de sedimentos. / The aim of this thesis was to evaluate the impacts of changes in land use and climate variability on water resources (discharge and sediment fluxes), into mesoscale (Piracicaba River basin) and small-scale (watershed Ribeirão das Posses) processes throughout a study of numerical modeling with SWAT model (Soil and Water Assessment Tool). Data of numerical model of terrain, soil maps and land use, temperature, precipitation, wind speed, solar radiation and relative humidity forced the SWAT model. The model showed a satisfactory performance in comparison with the observed data, as showed by the statistical indices of the Piracicaba River Basin (COE between 0.97 and 0.99 to 0.90 for flow and sediment fluxes) and Ribeirão das Posses (COE of 0.53 to 0.7 for flow and sediment fluxes). In simulations of changes in land use the results indicate that in both basins larger flows occur in the case of deforestation scenarios, being the scene of the pasture the highest values. The model corresponded to the evidence that peak flows, for example the events of flooding can be mitigated with reforestation and the scenario of anthropogenic with grasses for grazing land and sugar cane, extreme events tend to be further enhanced too. In assessing the simulation of sediment flows, the scenario of reforestation with eucalyptus shows reduction in soil loss, but still below the scenario reforestation with native vegetation, which presented the lowest values of sediment flux in both basins. In the simulation taking into account climate change, the results show increased flow to the future (2078-2098) and consequent increase in stream sediment, with an average 12% increase in the flows of Piracicaba and 19 % in the flow sediment. In Ribeirão das Posses this response pattern also occurred with a 46% increase in throughput and 40 % in the stream sediments.

Wind erosion is a global issue and affecting millions of people in drylands by causing environmental issues (acceleration of snow melting), public health concerns (respiratory diseases), and socioeconomic problems (costs of damages and cleaning public properties after dust storms). Disturbances in drylands can be irreversible, thus leading to natural disasters such as the 1930s Dust Bowl. With increasing attention on aeolian studies, many studies have been conducted using ground-based measurements or wind tunnel studies. Ground-based measurements are important for validating model predictions and testing the effect and interactions of different factors known to affect wind erosion. Here, a machine-learning model (random forest) was used to describe sediment flux as a function of wind speed, soil moisture, precipitation, soil roughness, soil crusts, and soil texture. Model performance was compared to previous results before analyzing four new years of sediment flux data and including estimates of soil moisture to the model. The random forest model provided a better result than a regression tree with a higher variance explained (7.5% improvement). With additional soil moisture data, the model performance increased by 13.13%. With full dataset, the model provided an increase of 30.50% in total performance compared to the previous study. This research was one of the rare studies which represented a large-scale network of BSNEs and a long time series of data to quantify seasonal sediment flux under different soil covers in southern Utah. The results will also be helpful to the managers for controlling the effects on wind erosion, scientists to choose variables for further modeling or local people to increase the public awareness about the effects of wind erosion.

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 thesis presents the results of contemporary limnological and palaeolimnological investigations of a series of crater lakes in order to reconstruct the palaeoenvironmental history of western Uganda, East Africa. The research examines questions of spatial and temporal heterogeneity of climate changes in the context of growing human impacts on the landscape over the last millennium. Sediment records from two lakes, Nyamogusingiri and Kyasanduka within the Queen Elizabeth National Park (QENP) were investigated to look at the long term records of climate and environmental change (spanning the last c. 1000 years). Five shorter cores across a land-use gradient were retrieved to assess the impact of human activity on the palaeoenvironmental record over the last ~150 years. High-resolution (sub-decadal), multiproxy analyses of lake sediment cores based on diatoms, bulk geochemistry (C/N and δ13C) and sedimentary variables (loss-on-ignition, magnetic properties and physical properties) provide independent lines of evidence that allow the reconstruction of past climate and environmental changes. This multiproxy approach provides a powerful means to reconstruct past environments, whilst the multi-lake approach assists in the identification and separation of local (e.g. catchment-scale modifications and groundwater influences) and regional effects (e.g. climatic changes). The results of a modern limnological survey of 24 lakes were used in conjunction with diatom surface sediment samples (and corresponding water chemistry) from 64 lakes across a natural conductivity gradient in western Uganda (reflecting a regional climatic gradient of effective moisture) to explore factors controlling diatom distribution. The relationships between water chemistry and diatom distributions were explored using canonical correspondence analysis (CCA) and partial CCA. Variance partitioning indicated that conductivity accounted for a significant and independent portion of this variation. A transfer function was developed for conductivity (r2jack = 0.74). Prediction errors, estimated using jack-knifing, are low for the conductivity model (0.256 log units). The final model was applied to the core sediment data.This study highlights the potential for diatom-based quantitative palaeoenvironmental reconstructions from the crater lakes in western Uganda. Sedimentary archives from the Ugandan crater lakes can provide high-resolution, annual to sub-decadal records of environmental change. Whilst all of the lakes studied here demonstrate an individualistic response to external (e.g. climatic) drivers, the broad patterns observed in Uganda and across East Africa suggest that the crater lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Warm Period (MWP; AD 1000-1200) and a relatively drier climate during the main phase of the Little Ice Age (LIA; c. AD 1500-1800); though lake levels in western Uganda do fluctuate, with a high stand c. AD 1575-1600). The general trends support the hypothesis of an east to west (wet to dry) gradient across East Africa during the LIA, however, the relationship breaks down and is more complex towards the end of the LIA (c. AD 1700-1750) when the inferred changes in lake levels at Nyamogusingiri and Kyasanduka are synchronous with changes observed at Lakes Naivasha (Kenya) and Victoria and diverge from local lake level records (from Edward, Kasenda and Wandakara). Significant changes in the lake ecosystems have occurred over the last 50-75 years, with major shifts in diatom assemblages to benthic-dominated systems and an inferred increase in nutrient levels. These changes are coincident with large sediment influx to the lakes, perhaps as a result of increasing human activity within many of the lake catchments.

Upland rivers control the large-scale topographic form of mountain belts, allow coupling of climate and tectonics at the earth’s surface and are responsible for large scale redistribution of sediment from source areas to sinks. However, the details of how these rivers behave when perturbed by changes to their boundary conditions are not well understood. I have used a combination of fieldwork, remotely sensed data, mathematical analysis and computer modelling to investigate the response of channels to well constrained changes in the forcings upon them, focussing in particular on the effects of glacial remoulding of the catchments draining the south flank of the Ladakh batholith, northwest Indian Himalaya. The last glacial maximum for these catchments is atypically old (~100 ka), and this allows investigation of the response to glaciation on a timescale not usually available. The geomorphology of the catchments is divided into three distinct domains on the basis of the behaviour of the trunk stream – an upper domain where the channel neither aggrades above or incises into the valley form previously carved by glacial abrasion, a middle domain where the channel incises a gorge down into glacial sediments which mantle the valley floor, and a lower domain where the channel aggrades above this postglacial sediment surface. This landscape provides a framework in which to analyze the processes and timescales of fluvial response to glacial modification. The dimensions of the gorge and the known dates of glacial retreat record a time averaged peak river incision rate of approximately 0.5 mm/y; the timescale for the river long profile to recover to a smooth, concave up form must exceed 1 Ma. These values are comparable with those from similarly sized catchments that have been transiently perturbed by changing tectonics, but have never been quoted for a glacially forced basin-scale response. I have also demonstrated that lowering of the upper reaches of the Ladakh channel long profiles by glacial processes can systematically and nonlinearly perturb the slope-area (concavity) scaling of the channel downstream of the resulting profile convexities, or knickzones. The concavity values are elevated significantly above the expected equilibrium values of 0.3-0.6, with the magnitude controlled by the relative position of the knickzone within the catchment, and thus also by the degree of glacial modification of the fluvial system. This work also documents the existence of very similar trends in measured concavities downstream of long profile convexities in other transiently responding river systems in different tectonoclimatic settings, including those responding to changes in relative channel uplift. This previously unrecognised unity of response across a wide variety of different environments argues that such a trend is an intrinsic property of river response to perturbation. Importantly, it is consistent with the scaling expected from variation in incision efficiency driven by evolving sediment flux downstream of knickzones. The pervasive nature of this altered scaling, and its implications for fluvial erosion laws in perturbed settings, have significant consequences for efforts to interpret past changes in forcings acting on river systems from modern topography. I follow this by examining in detail the channel hydraulics of the Ladakh streams as they incise in response to the glacial perturbation. I present a new framework under which the style of erosion of a natural channel can be characterized as either detachment- or transport-limited based upon comparison of the downstream distribution of shear stress with the resulting magnitude of incision. This framework also allows assessment of the importance of sediment flux driven effects in studied channels. This approach is then used to demonstrate that fluvial erosion and deposition in the Ladakh catchments is best modelled as a sediment flux dependent, thresholded, detachment-limited system. The exceptional quality of the incision record in this landscape enables an unprecedented calibration of the sediment flux function within this incision law for three different trunk streams. The resulting curves are not compatible with the theoretically-derived parabolic form of this relation, instead showing nonzero erosion rates at zero sediment flux, a rapid rise and peak at relative sediment fluxes of less than 0.5 and a quasi exponential decrease in erosional efficiency beyond this. The position of the erosional efficiency peak in relative sediment flux space and the magnitude of the curve are shown to be both variable between the catchments explored and also correlated with absolute sediment flux in the streams.

Changes in external forcing having traditionally been the main area of interest in trying to understand paleo-depositional environments in sedimentary systems; however, autogenic variability has been rising in importance, while autogenic behavior has been thought of as a “noise” generator. Recently, autogenic variability has been rising in attention because decoupling allogenic signatures (externally driven) from the stratigraphic record requires robust understanding of autogenic variations (internally generated). This study aims to quantitatively measure autogenic processes under a range of flux conditions and to show that autogenic processes generate distinct signatures rather than random noise. We present data from a matrix of nine different tank experiments in order to systematically evaluate the effects of sediment flux and water discharge variations on the autogenic timescale of fluvial sediment storage and release processes and the implications of this data to the stratigraphic record. The sediment flux tow ater discharge ratio and the absolute values of these two discharges control the autogenic timescale. Variations in sediment supply yield two competing effects on the autogenic timescale. The primary sediment flux control causes a reduction in the autogenic timescale as an increase in sediment supply yields an increased rate of filling the “fluvial envelope” (the space between the maximum and minimum fluvial slopes obtained during storage and release events). In contrast, the secondary sediment flux control increases the size of the fluvial envelope and works against the primary sediment flux control. Increasing the water discharge increases the autogenic timescale by widening the fluvial envelope during the organization of the fluvial system and more importantly, diminishes the functionality of the secondary sediment control. A competition exists between these factors, causing a non-linear range of autogenic timescales for a given sediment flux to water discharge ratio. In the nine experiments here, as the ratio decreases, the secondary effects of variations in sediment supply are suppressed by the relatively high water discharge, and the timescale is more predictable using the primary sediment control. As the ratio increases, the secondary effects from sediment supply are enhanced by a poorly organized fluvial system, and the timescale converges to a narrow range. This suggests significant implications for autogenic sediment delivery and stratigraphic development in a wide range of discharge conditions in field cases. / text

La thèse a pour objectif l'étude des plages sableuses enclavées, i.e. contraintes aux extrémités par des caps rocheux, soumises aux vagues et à un cycle de marée morte-eau vive-eau. Une double approche complémentaire liant études numériques et observations et mesures in situ sur un site-atelier a été retenue. Deux modèles déterministes basés sur les différents processus physiques (hydrodynamiques, hydro-sédimentaires et morphodynamiques) en jeu dans la zone littorale et moyennés sur la verticale (2DH) on été sélectionnés. Le code XBeach (Roelvink et al., 2009) utilise un maillage aux différences finies et intègre certaines spécificités tels qu'un modèle de propagation d'un rouleau d'écume ("roller"), un modèle de génération d'ondes longues et un modèle de développement d'un contre-courant de retour "undertow". Le code TELEMAC (Hervouet, 2007) utilise un maillage aux éléments finis. Pour le site-atelier, les plages enclavées adjacentes de La Palue et de Lostmarc'h en Presqu'île de Crozon (Finistère) ont été choisies pour leur bathymétrie complexe (présence de chenaux de baïne et d'un saillant) et leur géométrie complexe (caps rocheux de longueurs diverses, îlot). Une année d'observations et de mesures in situ (levés topographiques, pose de courantomètres ADV) a été entreprise entre le mois de septembre 2014 et le mois de septembre 2015, par diverses conditions météorologiques.Dans un premier temps, la dynamique globale des plages enclavées, représentées schématiquement par une échancrure rectangulaire, a été appréhendée. En particulier, la genèse d'une barre de déferlement en zone subtidale sous l'influence des dimensions de l'échancrure rocheuse, d'un cycle de marée morte-eau vive-eau et de houles énergétiques a été illustrée à travers plusieurs séries de simulations numériques à l'aide du code XBeach.Dans un deuxième temps, la modélisation hydrodynamique des courants sur les plages de La Palue et de Lostmarc'h a été effectuée, avec l'objectif d'étudier l'influence des caractéristiques des houles (hauteur, période et direction) et de celles de l'échancrure rocheuse (longueur des caps, espacement des caps, inclinaison des pointes) sur la prédiction des courants. Une ouverture sur la modélisation aux éléments finis (TELEMAC) en comparaison à celle aux différences finies (XBeach) a été présentée. Le code XBeach a été validé sur le plan hydrodynamique grâce aux mesures in situ d'une campagne de terrain réalisée en janvier 2015. Une étude numérique hydro-sédimentaire sur une lunaison complète (du 01 septembre 2015 au 29 septembre 2015) a alors été entreprise à l'aide du code XBeach, afin d'étudier l'intensité et la direction des flux sédimentaires instantanés et résiduels au gré des différents climats de houle et de marée, et selon les différents secteurs typologiques des plages de La Palue et de Lotsmarc'h. Cela a permis de mettre en évidence les particularités de la dynamique des plages enclavées par rapport aux plages ouvertes "quasi-infinies", tels que le phénomène de "contournement de cap", mais aussi les similitudes. Les résultats du code XBeach, pour différentes configurations du modèle, ont par ailleurs été comparés aux levés topographiques réalisés au cours du mois de septembre 2015.Dans un troisième temps, après une analyse statistique approfondie des climats de houle au large des plages de La Palue et de Lostmarc'h sur une période de 7 ans, l'impact morphodynamique de tempêtes extrêmes (houles décennale et cinquentennale) conjugué à celui de la hausse du niveau marin induit par le changement climatique, a été estimé sous la forme d'une étude numérique à l'aide du code XBeach sur un profil transversal au sud de la plage de La Palue / In this thesis, waves and neap-spring tide action on sandy embayed beaches constrained by rocky headlands is studied. A complementary approach combining numerical modeling and in situ measurements is used. Two deterministic model based on major physical processes (hydrodynamics, hydro-sedimentary and morphodynamics) present in the coastal zone and averaged over the water height (2DH) have been selected. XBeach (Roelvink et al., 2009) employs a finite difference scheme and incorporates some specific processes such as a roller, wave groups and the associated bound long wave and a undertow. TELEMAC (Hervouet, 2007) is a finite element scheme. Nearby sandy embayed beaches of La Palue and Lostmarc'h (Crozon Peninsula, Finistère) have been chosen for their complex bathymetry (rip channels, tombolo) and geometry (headlands, small island). One year of in situ measurements (topographical surveys, ADV velocimeters) between septembre 2014 and september 2015 has been undertaken, with different waves and tide climates.Firstly, the overall dynamics of embayed beaches built schematically in the form of a rectangular indentation has been caught. Especially, subtidal sandbar formation under the influence of waves, neap-spring tide and rocky headlands has been studied through several sets of numerical simulations.Secondly, hydrodynamic modelling on the embayed beaches of La Palue and Lostmarc'h has been made with the aim of study influence of waves characteristics (height, period and direction) and indentation's ones (headlands length, spacing between headlands, headlands inclination) on the prediction of currents. A simulation using finite element scheme (TELEMAC) has been achieved and compared to those using finite difference scheme (XBeach). XBeach currents predictions at two locations on the beaches of La Palue and Lostmarc'h over the period from the 21st January 2015 to the 23rd January 2015 have been compared to in situ measurements to validate the model. Whereupon, a numerical hydro-sedimentary simulation (using XBeach) over a full lunation from the 1st September 2015 to the 29th September 2015 has been undertaken on these two beaches, with the aim of study the intensity and direction of sediment flux (instantaneous and residual) for various waves and tide climates and for different morphological areas. This work has helped to highlight the dynamics features of embayed beaches compared to open beaches ones, such as headland sand bypassing, but also similarities. Moreover, XBeach morphodynamics predictions have been compared to in situ measurements for different model setup.Thirdly, after an in-depth statistical analysis of wave climates over a 7 year period offshore of La Palue and Lostmarc'h beaches, the morphodynamic impact of extreme storm waves (ten-yearly and fifty-yearly) combined to a sea level rise induced by climatic change on a cross-shore bottom profile south of La Palue has been estimated through a numerical study (using XBeach)

Thesis advisor: Noah P. Snyder / Salt marshes are hotspots for biodiversity, important carbon sinks, pollutant filtration systems, and buffers which strengthen coastal resiliency. Detailed geomorphic and sedimentary observations are vital to understanding the stability and sustainability of salt marshes in response to sediment placement restoration projects. Marsh stability is dependent on the suspended sediment and nutrients that are delivered to the marsh platform by meandering tidal channels. This study observed suspended-sediment fluxes at the mouth of Southeast Creek on Gull Island at Seven Mile Island Innovation Lab in coastal, southern New Jersey. The mesotidal, almost entirely low marsh, southern Gull Island received a recent dredge placement in fall 2020 of approximately 30,600 cubic meters of sediment from the adjacent New Jersey Intracoastal Waterway. Wetland instrumentation platforms to monitor post-dredge conditions were deployed summer 2021 and were removed in summer 2022. This instrumentation measured current velocity and depth time series at all platforms and suspended-sediment concentration using acoustic backscatter techniques at the mouth of Southeast Creek. This study is motivated by understanding the ongoing transport and deposition of dredged material placed on the marsh island. I found that velocities were ebb-dominant during all conditions. Concentrations on the flood phase of the tide were approximately half the magnitude of those seen on the ebb phases of the tide for normal circumstances while elevated concentrations were observed on ebbing and flooding currents for storms. A net export of 6.27 x 105 kg suspended sediment was observed through the tidal channel for all timescales throughout the deployment period. / Thesis (MS) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

A field survey was undertaken in Central Kalimantan, Indonesia (Borneo) to assess the extent and practices of Artisanal and Small-scale Gold Mining (ASGM), and to measure sediment and mercury flows in the provinces’ rivers. More than forty mining operations were visited in six of the provinces largest river basins during June, July and August of 2008. Based on the survey results, this thesis estimates that 43,000 small-scale gold miners in Central Kalimantan produced 13.3 tonnes of gold in 2008 (426,000 troy ounces - ozt) worth approximately 362 million CAD (based on 2008 international gold price of 850 CAD/ozt). Mercury use was ubiquitous for leaching gold from ores in the province. Approximately 65.3 tonnes was used for this purpose in 2008, with the majority of consumption- 80% by whole-ore amalgamation operations exploiting hard-rock deposits, but producing only 13% of the gold. These estimates have been interpolated using (i) measurements and detailed observations at more than forty ASGM operations surveyed in five different regencies; (ii) numerous interviews with miners, gold shops owners and officials across these regencies; and (iii) mapping of ASGM operations using satellite imagery. Hydraulic mining methods mobilize enormous volumes of sediment and native sediment-bound mercury. Sediment and mercury fluxes associated with ASGM activities were estimated based on a river sediment sampling campaign carried out in conjunction with the ASGM survey, and on subsequent modelling of river sediment transport. On streams and tributaries, mining activities increased sediment transport by factors between 100 and 1500, resulting in a net doubling of sediment loads on large first order river channels, on which the effects of mining are diluted in space and time by channels without mining. Particulate mercury flux sampled on six of Central Kalimantan’s largest river channels averaged 60ng/L ±33%, a high figure relative to most global rivers, despite average suspended sediment concentrations of only 75mg/L ±58%. Based on a hydrological and sediment transport model, 19.4 tonnes of mercury (±30%) transits these river systems annually, dominantly transported as suspended sediment load (95%), with the remaining 5% transported as bedload. Acute mercury exposure by inhalation during the burning of mercury-gold amalgam represents an important health concern at ASGM camps and gold shops. In relation to mercury, sector improvements should focus on eradicating whole ore amalgamation, and open burning of amalgam. Eliminating whole ore amalgamation requires technological improvements at the gold liberation (crushing and milling) and concentration stages of ore processing. Elimination of open-air burning can be achieved through education, and the use of retorts, fumehoods, and mercury re-activation cells– each of these basic technologies provide mercury users with economic incentives by reducing mercury consumption. / Graduate