Chemical leaching and specific surface area measurements of marine sediments in the evaluation of mercury contamination near cinnabar deposits

This paper investigates mercury contamination in recent marine sediment of the Tyrrhenian continental shelf near the mouths of three rivers draining an area with cinnabar deposits (M. Amiata, Italy). By means of chemical leaching, two fractions of the total mercury were distinguished: a ‘non-leachable’ fraction, consisting of mercury held in relatively stable forms and a ‘leachable’ fraction, composed of forms that are more weakly bound to the sediments. The two Hg fractions are correlated to the organic matter content, the distribution of which is strictly dependent on the sediment surface area.In order to eliminate the effects of grain size variations among the samples, the Hg concentrations were normalized to the unit of surface area (ng/m²). Following this procedure, the ‘non-leachable’ Hg was found to be concentrated mostly in a belt along the coast, while the ‘leachable’ Hg fraction was shown to accumulate largely in the zones with high depositional dynamics near the mouths of the rivers.Hypotheses to account for the discrepancy between the low concentrations of ‘leachable’ Hg in the sediment of the outer continental shelf and the high concentrations in the fauna of the same area, reported in previous papers, are presented.     

The distribution of mercury in the surficial sediments of the northern Tyrrhenian sea

Marine sediments are the ultimate recipient of mercury introduced into aquatic ecosystem either by man or by weathering. In the surficial sediments of the northern Tyrrhenian sea high concentrations of this metal were found in an area close to the effluent of a chlor-alkali plant and in the bays of La Spezia and Leghorn, which receive wastes from numerous industries and from port activities.The sediments of a much larger marine area off the mouths of the Ombrone, Albegna and Fiora rivers also contain high levels of Hg, part of which derives from the weathering of the rich cinnabar deposits of Mount Amiata and part from mining and processing the cinnabar.     

Short-term,linear, and non-linear local effects of the tides on the surface dynamics in a new,high-resolution model of the Mediterranean Sea circulation

Ocean Dynamics - The tides in the Mediterranean Sea are generally weaker than in other regions of the world ocean, but are locally intensified in passages with complex bathymetry, such as the...     

Trace metal assessment in sediment, molluscs and reed leaves in the bay of follonica (Italy)

Marine surficial sediments, intertidal molluscs and reed leaves collected in the Bay of Follonica are slightly contaminated by Pb, Ni, Zn and Fe. The main pollution sources are the waste water and the atmospheric emission of industrial plants. Probably, the weathering of the pyrite deposits along the eastern coast of Elba Island and adsorption and coprecipitation with hydrous Fe-Mn oxides increase the trace metal concentrations in sediments from the Piombino Channel. Mussels and limpets are contaminated by Hg because of the higher background level of the northern Tyrrhenian Sea.     

Benthic Community and Sediment Types: A Structural Analysis

Abstract. The distribution of the macrobenthic community, in relation to various physical and chemical characteristics of the sediment, was studied along the coast of Southern Tuscany (Central Tyrrhenian) in an area under the influence of the Ombrone River outflow.
The zonation of the benthos was found to be primarily under the control of a gradient of water movement, as is reflected by variations in the sediment structure from the coast to the open sea. This correlation is somehow influenced by secondary gradients such as the degree of mixing of the sediment and the deposition of terrigenous materials along the river plume.     

9th International Symposium on Environmental Biogeochemistry

Reports

9th International Symposium on Environmental Biogeochemistry     

Computational improvement of gravitational mode calculation of basins discretised by orthogonal curvilinear grids

The present note illustrates a criterion to improve the computational capability of the approaches proposed by Beltrami et al. [Beltrami, G.M., Bargagli, A., Briganti, R., 2003. Gravitational mode calculation of basins discretised by orthogonal curvilinear grids. Ocean Engineering 30, 833–853] for the direct numerical solution of the eigenvalue problem associated to the linear shallow-water equations when adiabatic boundary conditions apply. It is shown that—given the nature of its spatial differential operator—the problem can be solved by the singular value decomposition (SVD) of the real bidiagonal matrix resulting from a previous ad hoc Householder reduction of the operator matrix image. This procedure actually requires 1/8 of the random-access memory (RAM) needed by a standard library routine to compute all the eigenvalues and eigenvectors of the matrix image of the above-mentioned differential operator. Given the intrinsic limitation of a computing-machine RAM, this procedure dramatically improves the computational capability of both the proposed approaches.