Seasonal and depth variability of reduced sulphur species and metal ions in mud-flat pore-waters of the Venice lagoon
ABSTRACT An in-situ sampler was employed to monitor seasonal changes in the composition of pore-waters at different depths in a mud-flat located in the central part of the Lagoon of Venice, in proximity of the industrial area of Porto Marghera. The use of voltammetric methods of analysis allowed the simultaneous determination of concentrations of reduced S( − II), thiosulphate, Fe(II) and Mn(II) as well as zinc, lead, cadmium and copper ions. Other parameters such as the concentration of sulphate, Eh, pH and conductivity were also measured. Seasonal increases of S( − II) and Fe(II) concentrations in summer and autumn samples were observed, with the highest concentrations located at about 25 and 55 cm depth, respectively. An opposite seasonal dependence was observed for Mn(II) and S2O32− concentrations, which displayed higher values in winter: the highest concentrations were observed at a depth of 45 cm for Mn(II) and of 65 cm for thiosulphate. The concentrations of Cu, Cd, Pb and Zn ions showed a less evident seasonal variability. Top and bottom samples revealed high concentration values for zinc and copper ions, with the highest values in the 1,000–1,600 nM and 100–300 nM ranges, respectively. Cadmium and lead ions were present at lower concentrations, always less than 70 nM and 30 nM, respectively.
- [show abstract] [hide abstract]
ABSTRACT: The geochemical processes operating on metals in anoxic marine waters influence metal mobility and mode of transport to the sediments in a manner different from that observed in oxic regimes. In order to better understand these processes, dissolved and particulate Mn, Fe, Co, Ni, Cu, Zn, and Cd concentrations were determined in the water column of a permanently anoxic basin, Framvaren Fjord, Norway. Class specific behavior determines the degree to which these metals are involved in the processes of redox cycling at the O 2 / H 2 S interface and metal sulfide precipitation in the sulfidic water. Metal sulfide precipitation influences the magnitude of metal enrichment in the sediments. The transition metals, Mn, Fe, and Co, show active involvement in redox cycling, characterized by dissolved maxima just below the O 2 / H 2 S interface. Nickel concentrations appear unaffected by processes influencing the profiles of the other metals. The metals, Cu, Zn, and Cd, display a dramatic solubility decrease across the interface, are not involved in redox cycling, and are enriched in the sediments relative to a lithogenic component by factors of 11, 105, and 420, respectively. Ion activity products of the metals and sulfide provide evidence that chemical equilibria with a pure metal sulfide solid phase is not the dominant process controlling dissolved metal concentrations in the sulfide containing waters.Geochimica Et Cosmochimica Acta - GEOCHIM COSMOCHIM ACTA. 01/1985; 49(6):1433-1444.
- Journal of Sedimentary Research - J SEDIMENT RES. 01/1981;