Modelling metal speciation in the Scheldt Estuary: combining a flexible-resolution transport model with empirical functions

Predicting metal concentrations in surface waters is an important step in the understanding and ultimately the assessment of the ecological risk associated with metal contamination. In terms of risk an essential piece of information is the accurate knowledge of the partitioning of the metals between the dissolved and particulate phases, as the former species are generally regarded as the most bioavailable and thus harmful form. As a first step towards the understanding and prediction of metal speciation in the Scheldt Estuary (Belgium, the Netherlands), we carried out a detailed analysis of a historical dataset covering the period 1982-2011. This study reports on the results for two selected metals: Cu and Cd. Data analysis revealed that both the total metal concentration and the metal partitioning coefficient (Kd) could be predicted using relatively simple empirical functions of environmental variables such as salinity and suspended particulate matter concentration (SPM). The validity of these functions has been assessed by their application to salinity and SPM fields simulated by the hydro-environmental model SLIM. The high-resolution total and dissolved metal concentrations reconstructed using this approach, compared surprisingly well with an independent set of validation measurements. These first results from the combined mechanistic-empirical model approach suggest that it may be an interesting tool for risk assessment studies, e.g. to help identify conditions associated with elevated (dissolved) metal concentrations. © 2013 Elsevier B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A depth-averaged two-dimensional sediment transport model for environmental studies in the Scheldt Estuary and tidal river network

This paper presents the sediment module designed for the two-dimensional depth-averaged and one-dimensional section-averaged components of the finite-element model SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model) in the framework of its application to the tidal part of the Scheldt Basin. This sediment transport module focuses on fine-grained, cohesive sediments. It is a necessary tool to undertake environmental biogeochemical studies, in which fine sediment dynamics play a crucial role. The variables are the suspended sediment concentration (SSC) and the concentration of the sediments freshly deposited on the bottom. Sediment dynamics is controlled by the transport of SSC by advection and diffusion, while deposition and resuspension processes also depend on other physical, chemical and biological conditions . Besides building a functioning fine sediment transport model, the aim of this study is to identify, parametrize and quantify the key processes that are necessary to represent satisfactorily the suspended sediment dynamics in the Scheldt Estuary and tidal river network. It is known that the settling velocity of suspended sediments is influenced by flocculation. The important factors governing this process include the SSC itself, the turbulence, the shear stress, the salinity, the biological activity and some physicochemical properties (e.g. pH). In this sediment module, only SSC, salinity and biological activity are explicitely taken into account. In addition, the influence of the biological activity on the bottom layer erodibility is considered, as well as the mud proportion on the bottom, because the presence of sand increases the ability of the bottom layer to erode. Finally, the influence of a convergence zone between bottom currents carrying large amounts of fine sediments is also included in the model. The computer cost of a two-dimensional model is significantly smaller than that of the three-dimensional models traditionally deemed indispensable in sediment transport modeling. Even if the present simplified model is designed for the specific situation of the Scheldt, it produces results that are rather similar to those obtained with more complex, three-dimen-sional tools, but at a significantly lower cost. Therefore, it is believed that the model presented herein is suitable and useful for long-term environmental simulations in the Scheldt Estuary

A depth-averaged sediment transport model for environmental studies in the Scheldt Estuary and tidal river network

We present the sediment module designed for the two-dimensional depth-averaged and one-dimensional section- averaged components of the finite-element model SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model) in the framework of its application to the tidal part of the Scheldt Basin. This sediment transport module focuses on fine-grained, cohesive sediments. It is a necessary tool to undertake environmental biogeochemical studies, in which fine sediment dynamics play a crucial role. The variables are the suspended sediment concentration (SSC) and the concentration of the sediments freshly deposited on the bottom. Sediment dynamics is controlled by the transport of SSC by advection and diffusion, while deposition and resuspension processes also depend on other physical, chemical and biological properties. Besides building a functioning fine sediment transport model, the aim of this study is to identify, parametrize and quantify the key processes that are necessary to represent satisfactorily the suspended sediment dynamics in the Scheldt Estuary and tidal river network. The settling velocity of suspended sediments is influenced by flocculation. The important factors governing this process include the SSC itself, the turbulence, the shear stress, the salinity, the biological activity and some physicochemical properties (e.g. pH). In this study, only SSC, salinity and biological activity are explicitely taken into account. Moreover, the influence of the biological activity on the bottom layer erodibility is considered as well, along with the distribution of sediment types along the estuary, as the presence of sand increases the ability of the bottom layer to erode. Finally, the influence of a convergence zone between bottom currents carrying large amounts of fine sediments is also considered. The computer cost of a two-dimensional model is significantly smaller than that of the three-dimensional models traditionally deemed indispensable in sediment transport modeling. Even if the present simplified model is rather designed for a specific situation, it produces results that are rather similar to those obtained with more complex, three-dimensional tools, but also at a lower cost. Therefore, it is believed that the model presented herein is suitable for long-term environmental simulations in the Scheldt Estuary, especially when limited computer resources are available. This is the main achievement of the present study

Timing and placing samplings to optimally calibrate a reactive transport model: exploring the potential for Escherichia coli in the Scheldt Estuary

info:eu-repo/semantics/nonPublishe

GDF15/MIC1 and MMP9 Cerebrospinal Fluid Levels in Parkinson's Disease and Lewy Body Dementia.

Based on animal and ex-vivo experiments, Growth/Differentiation Factor-15 (GDF15, also called Macrophage Inhibitory Cytokine-1, MIC1), a member of the transforming growth factor-beta family, and Matrix Metalloproteinase-9 (MMP9), a member of the matrix metalloprotease family may be potential markers for Lewy body disorders, i.e. Parkinson's disease with (PDD) and without dementia (PDND) and Lewy body dementia (DLB). GDF15 has a prominent role in development, cell proliferation, differentiation, and repair, whereas MMP9 degrades, as a proteolytic enzyme, components of the extracellular matrix. In this study, cerebrospinal fluid GDF15 and MMP9 levels of 59 PDND, 17 PDD and 23 DLB patients, as well as of 95 controls were determined, and associated with demographic, clinical and biochemical parameters. Our analysis confirmed the already described association of GDF15 levels with age and gender. Corrected GDF15 levels were significantly higher in PDD than in PDND patients, and intermediate in DLB patients. Within Lewy body disorders, GDF15 levels correlated positively with age at onset of Parkinsonism and dementia, Hoehn & Yahr stage and cerebrospinal fluid t-Tau and p-Tau levels, and negatively with the Mini Mental State Examination. Remarkably, it does not relevantly correlate with disease duration. MMP9 was not relevantly associated with any of these parameters. Cerebrospinal GDF15, but not MMP9, may be a potential marker of and in Lewy body disorders

Timing and placing samplings to optimally calibrate a reactive transport model: exploring the potential for Escherichia coli in the Scheldt Estuary

info:eu-repo/semantics/nonPublishe

Design of a sampling strategy to optimally calibrate a reactive transport model: Exploring the potential for Escherichia coli in the Scheldt Estuary.

For the calibration of any model, measurements are necessary. As measurements are expensive, it is of interest to determine beforehand which kind of samples will provide maximal information. Using a criterion related to the Fisher information matrix as a measure for information content, it is possible to design a sampling scheme that will enable the most precise parameter estimates. This approach was applied to a reactive transport model (based on the Second-generation Louvain-la-Neuve Ice-ocean Model, SLIM) of Escherichia coli concentrations in the Scheldt Estuary. As this estuary is highly influenced by the tide, it is expected that careful timing of the samples with respect to the tidal cycle can have an effect on the quality of the data. The timing and also the positioning of samples were optimised according to the proposed criterion. In the investigated case studies the precision of the estimated parameters could be improved by up to a factor of ten, confirming the usefulness of this approach to maximize the amount of information that can be retrieved from a fixed number of samples. Precise parameter values will result in more reliable model simulations, which can be used for interpretation, or can in turn serve to plan subsequent sampling campaigns to further constrain the model parameters.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Correlation coefficients (r²) of CSF GDF15 and MMP9 and demographic, clinical and neurodegenerative parameters.

<p>Correlation coefficients (r²) of CSF GDF15 and MMP9 and demographic, clinical and neurodegenerative parameters.</p

Demographical, clinical and biochemical data of the included cohorts.

<p>Demographical, clinical and biochemical data of the included cohorts.</p