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Sediment dynamics of a tidal freshwater wetland system: A case study in the Biesbosch in the Rhine-Meuse delta
No full textMany deltas are threatened by land subsidence, sea level rise, and sediment starvation. The diversion of water and sediment into drowning delta wetlands aims at renewed sediment accumulation for ecosystem regeneration. This thesis investigates the Brabantse Biesbosch freshwater microtidal river system where new wetlands have been developed. The hydro-morphologic processes and their controls, and resulting sediment accumulation are investigated to determine critical conditions for sedimentation, and how these may be influenced or optimised. The major part of this project comprised collection and analysis of measurements of water and sediment flow, and sediment deposition. Furthermore, using the 1D SOBEK3 hydrodynamic and sediment transport model, a scenario analysis was exerted to explore future sediment accumulation. The two rivers are the major source of sediment for the area. The sediment load into the wetland system decreases with distance from the rivers. The new wetlands have improved river connectivity of the middle and northeast of the area, which results in less sediment depletion and thus more sediment accumulation. However, in channel sections close to the feeding rivers shear stresses are high, causing sediment resuspension during periods of increased river discharge. The newly developed wetland with continuous supply of river sediment effectively traps sediment, leading to positive sediment budget. In contrast, a new wetland at the interior of the Biesbosch functions as a source of material instead of a sediment trap, likely due to primary production within the wetland. Erosion occurs in inlet and outlet channels, whereas sediment is deposited in the central part of the wetlands. Both erosion and sedimentation rates have decreased over time, since channels reach morphodynamic equilibrium. Sand is deposited at the river inlets, and within and close to channels. Mud is more uniformly distributed over intertidal flats due to micro-topographic flow paths and shear stresses by wind waves that hamper sediment settling or cause resuspension at this bare and shallow area. Sediment fluxes vary at daily to weekly time scales due to river discharge, tide, and wind. Sediment deposition increases with upstream river discharge and sediment influx. However, trapping efficiencies decrease for increasing wind strengths and raised river discharges, due to the associated increased shear stress in the water, preventing settling or even causing resuspension of previously deposited material. An efficient freshwater tidal wetland system would comprise multiple proximal flow through or dead-ending tidal channels, with limited length, so not all sediment is progressively lost at short distance from the river. The connectivity between channels and intertidal area can be improved by a reduction of the total gradient of the intertidal zone, so large areas will submerge during high water. Furthermore, resuspension of sediment by wind or flow related shear stresses should be reduced
Impact of Chelicorophium curvispinum on the concentration-discharge response of suspended sediment in the Rhine River
Get PDFIn an ongoing study to the decline in suspended sediment concentrations and loads in the Rhine river since the mid-1950s, the temporal changes in the power-law sediment rating curve parameters were examined. This revealed that the rating exponent of the rating curve increased substantially between the early and late 1980s. Until the early 1980s, the ratings curves were relatively flat with values of the rating exponent b varying around 0.2. In the mid-1980s, the exponent suddenly increased to a value between 0.4 and 0.6 and since then has remained within this range. This change in the rating exponent was mainly caused by a decrease in suspended sediment concentrations during low discharges. During high discharges, the suspended sediment concentration initially increased during the late 1980s, but this increase was nullified soon afterwards due to the declining trend in suspended sediment concentration. The sudden increase of the rating exponent coincided with the period that the Ponto-Caspian Chelicorophium curvispinum (Caspian mud shrimp) invaded the Rhine river basin. This suggests that this suspension-feeder species bears the prime responsibility for this increase, although this hypothesis requires further independent evidence. The sudden increase in the rating exponent does however not manifest itself in the long-term gradual trend of declining suspended sediment concentrations and vice versa. Apparently, the sequestration of sediment by Chelicorophium curvispinum is only temporary: the suspended sediment sequestered during periods of relatively low discharges is likely remobilised again during periods of high discharge. This implies that the invasion of Chelicorophium curvispinum has not played a significant role in the decline of suspended sediment concentrations. The precise reasons for the gradual long-term decline in suspended sediment concentration remain yet unknown
Sediment dynamics of a tidal freshwater wetland system: A case study in the Biesbosch in the Rhine-Meuse delta
No full textMany deltas are threatened by land subsidence, sea level rise, and sediment starvation. The diversion of water and sediment into drowning delta wetlands aims at renewed sediment accumulation for ecosystem regeneration. This thesis investigates the Brabantse Biesbosch freshwater microtidal river system where new wetlands have been developed. The hydro-morphologic processes and their controls, and resulting sediment accumulation are investigated to determine critical conditions for sedimentation, and how these may be influenced or optimised. The major part of this project comprised collection and analysis of measurements of water and sediment flow, and sediment deposition. Furthermore, using the 1D SOBEK3 hydrodynamic and sediment transport model, a scenario analysis was exerted to explore future sediment accumulation. The two rivers are the major source of sediment for the area. The sediment load into the wetland system decreases with distance from the rivers. The new wetlands have improved river connectivity of the middle and northeast of the area, which results in less sediment depletion and thus more sediment accumulation. However, in channel sections close to the feeding rivers shear stresses are high, causing sediment resuspension during periods of increased river discharge. The newly developed wetland with continuous supply of river sediment effectively traps sediment, leading to positive sediment budget. In contrast, a new wetland at the interior of the Biesbosch functions as a source of material instead of a sediment trap, likely due to primary production within the wetland. Erosion occurs in inlet and outlet channels, whereas sediment is deposited in the central part of the wetlands. Both erosion and sedimentation rates have decreased over time, since channels reach morphodynamic equilibrium. Sand is deposited at the river inlets, and within and close to channels. Mud is more uniformly distributed over intertidal flats due to micro-topographic flow paths and shear stresses by wind waves that hamper sediment settling or cause resuspension at this bare and shallow area. Sediment fluxes vary at daily to weekly time scales due to river discharge, tide, and wind. Sediment deposition increases with upstream river discharge and sediment influx. However, trapping efficiencies decrease for increasing wind strengths and raised river discharges, due to the associated increased shear stress in the water, preventing settling or even causing resuspension of previously deposited material. An efficient freshwater tidal wetland system would comprise multiple proximal flow through or dead-ending tidal channels, with limited length, so not all sediment is progressively lost at short distance from the river. The connectivity between channels and intertidal area can be improved by a reduction of the total gradient of the intertidal zone, so large areas will submerge during high water. Furthermore, resuspension of sediment by wind or flow related shear stresses should be reduced
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Compositional dynamics of suspended sediment in the Rhine River: sources and controls
Get PDFPurpose: Information on the geochemical composition of suspended sediments in rivers is crucial to identify sediment source type or area. In large river basins, however, the relation between sediment composition and its controlling factors is often obscured. This study aims to assess and improve the conceptual understanding on the factors and mechanisms that control the composition of suspended sediments in the River Rhine, one of the large European rivers, and to identify the dominant source types of elements. Materials and methods: We performed log-linear regression analysis and principal component analysis (PCA) on bi-weekly monitoring data of suspended sediment composition, supplemented with daily measurements of suspended sediment concentrations (SSC) and discharge at the Lobith monitoring station near the German-Dutch border for the period 2011–2016. Results and discussion: The statistical analyses show a consistent grouping of elements that display contrasting temporal variation or different responses to increased discharge. The contrasting behaviour also becomes manifest in the results from the PCA. A first component that explains about the half of the total variance in the entire dataset reflects the variation in clay content in the suspended sediment. A second component reflects anthropogenic pollution and explains about a quarter of the total variance. A third component probably reflects variation in sediment provenance. Conclusions: The majority of the temporal variation in suspended sediment composition can be attributed to variations in grain size (clay content), organic matter content, and anthropogenic pollution. Only a minority of the variation can be attributed to variations in the contributions from different upstream source areas. This variation represented by the third and higher components from the PCA can potentially be used for sediment provenance analysis
Correction to: Compositional dynamics of suspended sediment in the Rhine River: sources and controls (Journal of Soils and Sediments, (2020), 20, 3, (1754-1770), 10.1007/s11368-019-02490-5)
No full textTable 4 in the originally published article is not correct
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Drowning or emerging: the effect of climate change on the morphology of tidal freshwater wetlands
No full textTidal wetlands provide a habitat for a wide range of vegetation communities and animal species that are found nowhere else, and also provide a wide range of social, economic and environmental services to human well-being. Tidal wetlands are under threat of drowning by sea level rise (SLR) as a result of climate change (CC). Enhancing sedimentation inside tidal wetlands is currently one of the main mitigating measures to prevent wetlands from drowning due to SLR. Tidal freshwater wetlands (TFWs) in the transition zone between tidally-dominated and fluvially-dominated sections of a river delta have received little attention in scientific literature. This study focused on which factors control sedimentation and erosion in tidal freshwater wetlands and how climate change affects these controls and thus sedimentation and erosion. To study how sedimentation rates and patterns in TFWs are affected by the interplay of river discharge, wind waves and tide, a hydro-morphodynamic model was constructed of a small de-embanked polder located in the Brabantse Biesbosch TFW in the Rhine-Meuse delta in the Netherlands. This model was used to carry out multiple scenario analyses to examine how different combinations of hydro-meteorological boundary conditions control sedimentation and erosion under current climate conditions. Next, transient scenario runs were carried out for the period 2015-2050 with gradually changing boundary conditions in order to assess current and future net sedimentation rates, patterns and trapping efficiencies, and compare predicted rates of bed level change to predicted rates of SLR. After that, the effect of climate change as well as river diversions on sedimentation patterns and trapping efficiencies of the entire Brabantse Biesbosch wetland was analyses. TFWs depend on riverine discharges for inflow of water & sediment, but more discharge does not automatically mean more sedimentation: in the Brabantse Biesbosch, larger discharge events generally lead to a net loss of sediment due to resuspension and outflow of previously settled material. Wind as a boundary condition has a major effect on sedimentation rates and trapping efficiencies, and only negative. The effect of tidal range on sedimentation rates is more limited than the effect of wind and discharges; however this strongly depends on the location of the wetland in the delta. The de-embanked polder study area is likely to drown due to CC. The effect of CC on sedimentation rates and morphological developments is limited: morphological stabilization of this newly developed area is a far more important driver of bed level changes than CC. TFWs are dynamic, complex systems in which the sedimentation rates are controlled by the interplay between river discharges, tides, wind and wetland characteristics. There is not a single ‘perfect measure’ that can be applied everywhere to enhance sedimentation rates. For example, the construction of river diversions towards wetlands is only effective in case the SSC of the feeding river is sufficiently high to counteract the eroding effect of the incoming current
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