Influence of diagenetic processes on the distribution and accumulation of major and trace elements in the sediments of the Scheldt estuary

Sediment cores were carefully collected with a box corer in three areas of the Scheldt estuary (Antwerpen, Doel, Terneuzen) in August and repeated in December. The 20 upper cm were sliced under a nitrogen atmosphere in 0.5-1 cm thick layers. The slices were then centrifuged in order to separate the interstitial water from the solid phase. The following elements were determined in the solid phase Si, Al, Fe, Ca, Mg, Mn, Co, Zn, Cd, Cu, Pb, Corg and Norg. In addition, the following parameters were also measured in the pore waters: salinity, alkalinity, DIC, pH, DOC, NO3, NH4, PO4, Si, Fe, Ca, Mg, Mn, Co, Zn, Cd, Cu and Pb. The results for one core taken as an example will be shown on the poster. The vertical distribution of most major and minor elements remains rather constant except that of organic carbon whose concentration profile is scattered, reflecting the presence of thin mud layers and lenses in sandy deposits. The vertical profile of dissolved elements in pore waters exhibit generally marked gradients linked to the bacterial degradation of organic matter imposing strongly reducing conditions below the water-sediment interface. This is demonstrated by the rapid decrease of nitrate, the release of manganese and iron and finally the consumption of sulfate. The concentrations of trace elements fluctuate markedly in relation to dissolution and precipitation reactions. In order to obtain additional information on the speciation of trace elements, titration experiments of the solid phase by HCl have been performed during which the release of major and minor elements are measured. The similarity in behaviour between elements allow to demonstrate their close association. This is for example the case of Mn and Co; Zn, Cd and S=; Cu and Al; Pb and Fe. The use of a diagenetic model proposed by Yifenga and Van Cappellen (1996 ) is presently tested and tentatively improved to include the description of the behaviour of trace elements. Preliminary results will be shown

Sedimentologisch onderzoek van de Spuikom te Oostende

Thirty sediment samples of the Scour Basin in Ostend were analysed for the boulder content, detric elements, carbonates, organic material and their Zn, S, Cu, Mn and P concentration were determined. Then correlations between all these factors were determined. The spread of most factors appeared bound to those of the boulder

Geochemical properties of sediments in the Scheldt estuary with emphasis on trace metals

Surficial sediment of the Scheldt estuary were collected with a Van Veen grab at 57 stations between Temse and Vlissingen. They were analyzed for major elements (Si, Al, Fe, Ca, Mg, Na, K, Corg, Cinorg, Norg and P) and trace metals (Mn, Cr, Ni, Co, Zn, Cu, Cd, Pb, Li). Factor analysis indicates that 44% of the variance can be explained by one factor which exhibits a high saturation for trace metals, organic matter, Al and Fe, all variables typical of fine muds. The high scores of this first factor are almost exclusively present in the upper estuary except for one area in front of Terneuzen. The second factor which explains 23% of the variance is typical of the carbonates and the third one (19% of the variance) is representative of the clay minerals. These two factors are more evenly distributed over the estuary. As usual, there is a strong influence of granulometry on the distribution of elements in the sediments. Intercomparaison of their composition within the Scheldt or with other aquatic systems require thus a normalization procedure. This problem has been studied in detail by analysing various size fractions (63-16:; 16-8:; 8-4:;<4:) separated by elutriation or by using a typical parameter of the fine fraction such as the specific surface area of the samples or the concentration of a selected element ( Al, Fe, Li, Corg). The normalization of trace metals allowed us to evaluate an enrichment factor of the trace elements in the estuarine deposits due to man’s activities. In addition, it allows also to demonstrate the marked decrease of the anthropogenic impact by comparing the composition of sediments collected in 1976 and in 1994. Finally, we have developed a new method based on the titration of the suspended sediment with HCl, which allows to gain information on the speciation and potential reactivity of trace metals. This method indicates the Zn and Cd are associated with sulfides and are rather reactive. Copper is released together with Al indicating a possible link of this element with clay mineral whereas Pb and Cr are redissolved together with Fe. The dissolution curve also indicates that Mn is present as rhodochrosite in the easily dissolving carbonate phase and as oxy-hydroxide in the more refractory phase. Mn is strongly correlated to Co

Kinetic models of diagenesis in disturbed sediments Part 2. Nitrogen diagenesis

This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right. © 1977, by the Association for the Sciences of Limnology and Oceanography, Inc.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Atmospheric CO₂ fluxes in a highly polluted estuary (the Scheldt)

Dissolved CO2 concentration and exchange with the atmosphere were investigated simultaneously in the Scheldt estuary. CO2 partial pressures as high as 5,700 µatm, corresponding to oversaturation with respect to the atmosphere of 1,600%, were observed in the upper estuary. The corresponding atmospheric CO2 fluxes reached values of up to 1.2 mol m-2 d-1. The estimated flux for the entire estuary amounts to 600 t of C d-1 for a river discharge of 6 m3 d-1

Suspended solids, light penetration and primary production in the Scheldt estuary

In strong tidal estuaries such as the Scheldt, the hydrodynamic conditions display large variations, with current velocities ranging from zero during slacks up to 2 m.s-1 during ebbs and floods. This highly fluctuating water velocity induces a periodically varying shear stress at the sediment-water interface, resulting in a cyclic pattern of sedimentation and resuspension. As a result, the suspended solid concentration in the water column follows a marked tidal fluctuation which causes significant variations of the light-attenuation coefficient. Since the underwater light field depends on both the incident light and the light-attenuation coefficient, the instantaneous light availability (PAR) in the water column has to be computed from these two periodic signals. In this paper, we present some characteristics of the underwater light field in the Scheldt estuary. We show that the estimation of gross primary production (GPP) by phytoplankton is strongly affected by the time-variation of the light-attenuation coefficient (kd). In particular, the common practice of considering a constant (time-averaged) kd value leads to an erroneous assessment of the time- and depth-integrated GPP. Finally, we show some estimates of the phytoplankton net primary production (NPP) in the Scheldt, computed from a coupled model that takes into account the hydrodynamic conditions, the light penetration and the phytoplankton dynamics