The Wax Lake Delta (WLD) is one of the few areas of land gain in coastal Louisiana and provides an analog for a naturally developing subdelta created by a river diversion. This study examined the spatial and temporal variability of benthic respiration to broaden our current understanding of the biogeochemical functioning of diversion-created estuarine systems. Spatial and seasonal benthic respiration rates were quantified during distinct periods of discharge and water temperature conditions, which included a spring period of peak river discharge (May 2012, 2013), a summer period of low discharge and maximum seasonal water temperatures (August/Sept, 2012), and an autumn period of low discharge and intermediate water temperatures (October 2013). Benthic respiration rates for the Wax Lake Delta ranged from 4.4 – 46.8 and averaged 16.7 (± 1.5) mmol O2 m-2 d-1 . Atchafalaya Bay sites ranged from 10.3 - 26.5 and averaged 17.1 (± 1.5) mmol O2 m-2 d-1 across all sites and seasons. Benthic respiration generally increased along two spatial gradients: 1) with distance offshore from the delta into Atchafalaya Bay, and 2) toward the interior of a mouth bar island. These patterns were related to similar increases in sediment OC and N content, which were derived from a mix of terrigenous and marine sources and varied with season. Sediment organic (OC and N) content and water temperature were identified as main drivers influencing benthic respiration in the Wax Lake Delta estuary. Seasonal changes in riverine discharge and wind-driven sediment resuspension events were likely to influence the seasonal variability of benthic respiration by governing water temperature and organic matter supply to the sediments. Benthic oxygen consumption rates in the Wax Lake Delta were most sensitive to increases in water temperature during low discharge conditions (< 2,000 m3 /s) of the MI-AR system. In context of coastal restoration, results from this study suggest that opening a sediment diversion during spring peak discharge conditions will have less of an effect on benthic oxygen consumption rates than during warmer low flow conditions. / acase@tulane.edu

This research focuses on how sediment supply, sea level and delta processes control the partitioning of the sediment budget across and into the topset, slope and basinfloor compartments of deepwater basins. Addressing this problem provides significant insight to characterize source-to-sink systems, improve tectono-stratigraphic models and predict sand bypass to deepwater areas. The research was carried out in the Lance-Fox Hills-Lewis shelf margin formed during the Maastrichtian in the Washakie-Great Divide basin of southern Wyoming. I use a database with approximately 520 wells integrated with outcrops to develop a high resolution, dynamic stratigraphy approach for shelfmargin characterization. The results emphasize the driving role of sediment supply in rapid shelf-margin building and deepwater sand emplacement. On the study margin, high sediment supply was able to outpace shelf accommodation even at times of relatively high and rising sea level. At these times, shelf margin clinoforms developed a more aggradational architecture with relatively thick and more marine influenced topsets formed in response to basin deepening due to rapid subsidence. The high supply and subsidence are interpreted to have resulted from crustal loading and significant erosion during prominent Laramide thrust-driven source uplift. The high supply caused the formation of highstand shelf-edge deltas with strong wave and river influences. These deltas resulted in extensive coastal sand belts at the shelf margin, and bypass of significant volumes of sand to deepwater areas. In contrast, during times of stable to very low rates of sea level rise, the basin developed more progradational clinoforms with more terrestrial and generally thinner topsets. More of the sediment was funneled to the basin floor and shelfedge deltas were under strong river and tidal influence. Stable or even falling sea level resulted from decreased subsidence or slight basin uplift, interpreted to have resulted from decreasing uplift, tectonic quiescence or possibly slight tectonic rebound in the basin. The Lewis-Fox Hills margin is considered supply-dominated, a term to denote moderately deep shelf margins (< 1000 m) that prograde at high rates (several tens of km/my) and deliver sand to deepwater areas recurrently and in large volumes even at sea level highstand.

Submitted by Patricia Barros (patricia.barros@ufes.br) on 2016-07-11T17:45:43Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação final Tarcila oficial (1).pdf: 1813884 bytes, checksum: 756128602e875dcb32bc26ce60ad8a9c (MD5) / Approved for entry into archive by Patricia Barros (patricia.barros@ufes.br) on 2016-07-11T17:45:59Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação final Tarcila oficial (1).pdf: 1813884 bytes, checksum: 756128602e875dcb32bc26ce60ad8a9c (MD5) / Made available in DSpace on 2016-07-11T17:45:59Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação final Tarcila oficial (1).pdf: 1813884 bytes, checksum: 756128602e875dcb32bc26ce60ad8a9c (MD5) / Na cidade de Linhares (ES) o rio Doce deságua no Oceano Atlântico formando uma feição deltaica na Plataforma Continental adjacente. Os sedimentos que compõem o delta tem origem na bacia hidrográfica do Rio Doce que é a maior em volume de vazão em /s e área de drenagem do estado capixaba. Ao longo das últimas décadas a bacia passou por um intenso processo de ocupação, transformação e interferências diretas no canal principal. O objetivo do presente trabalho foi analisar proxies geoquímicos presentes no depósito deltaico do rio Doce e determinar um padrão deposicional através do comportamento dos elementos. Para isso foram realizadas análises sedimentológicas, de teor de matéria orgânica e nutrientes, concentração de metais e taxa de sedimentação em testemunhos coletados na plataforma continental adjacente a desembocadura do rio Doce, DT01 SUL (coletado ao Sul da desembocadura), DT02 NORTE (ao Norte) e suas respectivas réplicas, DT01R SUL e DT02R NORTE. Os testemunhos apresentaram composição de granulometria fina em sua maioria com maiores percentuais em DT01 SUL em relação a DT02 NORTE. O conjunto dos resultados obtidos para teor de água, densidade e porosidade identificaram um pacote sedimentar de deposição recente em DT01R SUL e sedimentos em DT02R NORTE com maior compactação. Sendo os pontos equidistantes da desembocadura, as maiores taxas de sedimentação encontradas em DT01R SUL indicam o maior aporte de sedimento para a região Sul em relação a região Norte, onde foi coletado o testemunho DT02R NORTE. Não foi possível identificar a fonte efetiva do material orgânico em DT01 SUL a partir da razão C/N, visto que os resultados situaram-se na faixa de transição entre fontes terrestres e marinhas. Em DT02 NORTE ficou clara a importância da produção autóctone visto que a razão C/N ficou na faixa da matéria orgânica de origem marinha. Os valores de Cu estiveram próximos aos naturais com algumas exceções principalmente em DT01 SUL. Já os valores de Pb excederam o valor encontrado no background em ambos os testemunhos podendo indicar maior influência do aporte antrópico. Assim, por meio dos resultados obtidos do comportamento de proxies no delta do Rio Doce foi possível identificar uma deposição preferencial do sedimento fino transportado pelo rio através da Plataforma Continental adjacente em direção ao Sul da desembocadura. / In the Linhares city (Espírito Santo State), the Doce River empties into the Atlantic Ocean forming a deltaic feature on the Continental Shelf. The sediments that make up the delta come from the Doce River basin that is the largest in volume flow e drainage area in the State of Espirito Santo. Over the last decades the basin has undergone an intense process of occupation, processing e direct interference in the main channel. The objective of this study was to analyze geochemical proxies present at the Doce River deltaic deposit e determine a pattern of behavior by these depositional elements. For analyzes were performed sedimentological characteristics, organic matter e nutrients contents, metals concentration e sedimentation rates in cores collected on the continental shelf adjacent to the mouth of the Rio Doce. The cores were DT01 SOUTH (collected south of the mouth), DT02 NORTE (collected north) e their replicas, DT01R SOUTH e DT02R NORTE. The cores presented a composition of higher percentage of fine sediments in DT01 SOUTH compared to DT02 NORTE. The set of results obtained for water content, density e porosity identified a package of sedimentary recent deposition in DT01R SOUTH e DT02R NORTE sediments with higher compression. Being the points equidistant from the mouth, the highest sedimentation rates found in DT01R SOUTH indicate the major input of sediment to the South compared to the North. The C/N ratio in DT01 SOUTH was unable to identify the source of the organic material since the results were located in the transition zone between land e marine sources. In DT02 NORTH became clear the importance of autochthonous production as the C/N ratio was in the range of organic matter with marine origin. Cu values were close to natural with some exceptions mainly in DT01 SOUTH. The values of Pb exceeded the value found in the background on both cores may indicate a greater influence of anthropic contribution. Thus, the results obtained through the behavior of proxies in the delta of Rio Doce was possible to identify a preferential deposition of fine sediment carried by the river via the Continental Shelf adjacent to the South of the mouth.

Thesis advisor: Noah P. Snyder / Reservoir sedimentation is a significant issue not only because it limits a reservoir’s water storage capacity and threatens its ability to meet environmental and societal needs, but also because it reduces the amount of sediment reaching downstream coastal ecosystems where sediment loading sustains critical habitat for wildlife and fisheries. Reservoir deltas in particular can decrease channel capacity and lead to an increased flood risk for populations living in the alluvial plain upstream of dams; however, studies of these landforms are underrepresented in the literature. To address that knowledge gap, this project examines reservoir sedimentation in Lake Seminole, a 123 km² surface-water impoundment created in 1954 and located at the junction of the Chattahoochee and Flint Rivers in Florida and Georgia. Where it enters Lake Seminole, the Chattahoochee River has a large subaerial delta that is actively prograding. High-resolution topographic and bathymetric datasets and historical cross section data were analyzed to measure the evolution of this delta and characterize subaerial and subaqueous sedimentation in the reservoir more broadly. In addition, a comparative land-cover change analysis was conducted for the three watersheds that drain to Lake Seminole to explore potential links between the suspended sediment generated by these surface disturbances and sedimentation patterns in each arm of the reservoir. Across the entire reservoir body, subaqueous sediment accumulated at a rate of 0.81 cm/yr between 1957–1976 and 0.12 cm/yr between 1976–2009, with the highest sedimentation rates occurring shortly after dam construction. Within the Chattahoochee arm, subaqueous sediment accumulated at a rate of 2.79 cm/yr between 1957–1976 and 0.68 cm/yr between 1976–2009, whereas, in the Flint arm, subaqueous sedimented eroded at a rate of -0.21 cm/yr between 1957–1976 and accumulated at a rate of 0.08 cm/yr between 1976–2009. Qualitative observations indicate that the erosional signal in the Flint is focused in the upstream-most portion of the arm and a depositional signal emerges farther downstream. On the Chattahoochee River delta, subaerial sediment accumulated at a rate of 1.46 ± 0.48 cm/yr between 2007–2018, with the most rapid areas of aggradation (> 4.5 cm/yr) located around the exterior edges of the delta islands. No strong link was found between the percentage of each watershed that underwent land cover change and the sedimentation rates in each reservoir arm. This analysis will provide new insights into the physical processes of reservoir sedimentation that can be used to inform river management practices and decrease the negative impacts of sediment trapping not only within reservoirs, but also upstream and downstream of dams. / Thesis (MS) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Les deltas fluviaux sont des écosystèmes riches et vulnérables. Les apports de sédiments fluviaux assurent leur développement face à la subsidence et l’érosion induite par les agents marins. Les deltas sont principalement exposés à des crues et des submersions marines. Pourtant, ils restent des lieux stratégiques de peuplement, de production économique et d’enjeux géopolitiques, les rendant d’autant plus vulnérables et exposés aux risques. Cette thèse a pour objectif de cerner le fonctionnement passé et actuel de ces systèmes à partir de l’analyse de soixante deltas et d’une approche holistique systémique, à l’aide de données spatiales, environnementales et sociétales. Après l’étude de l’évolution côtière récente montrant une tendance à la diminution de la progradation de nombreux deltas, une classification conceptuelle et qualitative de la morphologie des deltas axée sur les influences fluviomarines a été conduite. La mise à jour de cette classification et la proposition de nouvelles approches, en termes de morphologie, de dynamique et de vulnérabilité, ont nécessité une revue des acquis antérieurs, une quantification de l’influence du fleuve, de la houle et de la marée, et une approche quantitative qui a mis en évidence la complexité des interactions. Le travail débouche sur une nouvelle classification quantitative et objective. La thèse compare aussi les réponses deltaïques à des perturbations exceptionnelles, montrant les limites de la résilience deltaïque. Elle renseigne sur l'impact anthropique sur ces espaces fragiles fortement dépendants de l’apport sédimentaire. Cet équilibre est d’autant plus fragilisé aujourd’hui par les impacts du changement climatique. / River deltas are rich and fragile ecosystems. Deltas depend on fluvial sediment supply to balance natural subsidence and erosion caused by waves and currents. Deltas are mainly affected by river flooding, marine submersion. However, deltas are strategic sites of human settlement, economic hotspots, and geopolitical issues. This attraction increases the pressure, rendering these deltas more and more exposed to risks and vulnerable.The main objective of this thesis is to analyze the past and present functional dynamics of delta shorelines based on 60 of the world’s deltas and a holistic and systemic approach with spatial, environmental, and societal data. After the study of recent coastal evolution showing a tendency to decreasing progradation of many deltas, a conceptual and qualitative classification of deltaic morphology based on fluviomarine influences was conducted. Updating of this classification and the proposal of new approaches, in terms of morphology, dynamics, and vulnerability, have necessitated revisiting these older schemes, and the adoption of a methodological and interpretative approach aimed at quantification of the weight of each of these three parameters showing the complexity of the interactions. The thesis proposes a new quantitative and objective classificatory framework, including the human dimension. Finally, the thesis highlights the responses of deltaic shorelines to exceptional perturbations, and highlights the limits of resilience. The thesis advises over the impact of humans on these fragile coastal environments, the equilibrium of which strongly depends on sediment supply. This fragility is further exacerbated by the impacts of climate change.