Geochemical cycling of heavy metals in a marine coastal area: benthic flux determination from pore water profiles and in situ measurements using benthic chambers

Abstract

Concentrations of the heavy metals Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured in sea water, suspended matter, sediments and pore water samples collected in a coastal area of the middle Tyrrhenian Sea . Concentration factors between pore water (extracted from the first centimeter of the sediments) and the overlying sea water (taken 30 cm above the sea bed) were less than 1 for Cr, Cu and Pb, 1-10 for Cd and Ni, 10-100 for Fe and Co, 100-1000 for Mn, and 1-100 for Zn .The benthic fluxes of heavy metals at the sediment-water interface were measured directly using in situ benthic chambers and calculated using Fick's first law during two experimental periods, one in 1986 and the other in 1988 . The fluxes of Cu, Ni, Pb and Zn varied significantly over time ; this appeared to be related to their relatively low (<_ 10) concentration factors . From the benthic chamber experiments, metals with positive fluxes were in the order : Mn > Fe > Co > Cd, while those with negative fluxes were : Zn > Pb > Ni Cu. Fluxes calculated using Fick's Law were : positive -Mn > Fe > Zn (or Zn > Fe) > Ni > Co > Cd, negative fluxes Pb > Cu > Cr .Measured (benthic chamber) and calculated (Fick's first law) fluxes for Co, Cd, Mn, Pb and Fe were comparable within an order of magnitude, although less agreement was found for Cu, Ni and Zn . Removal of Ni and Zn at the sediment-water interface has been proposed to explain the fact that the measured and calculated fluxes have opposite directions for these metals .

Porewater dynamics of silver, lead and copper in coastal sediments and implications for benthic metal fluxes

“…The average porewater concentrations of Cu and Pb at each site are statistically equivalent (at the 95% certainty level). These values fall within the range reported for a variety of aquatic environments and human impacts including the Tyrrhenian Sea (Ciceri et al, 1992), Laurentian Trough (Gobeil and Silverberg, 1989), San Francisco Bay (Rivera-Duarte and Flegal, 1994Flegal, , 1997b, the coastal North Sea (Gao et al, 2009), the Gironde Estuary (Audry et al, 2006(Audry et al, , 2007, Bolivian Altiplano lakes (Tapia and Audry, 2013) and an Iberian Ria (Santos-Echeandia et al, 2009).…”

Dissolved Heavy Metal (Cd, Pb, Cr, Ni) Concentrations in Surface Water and Porewater from Bahía Blanca Estuary Tidal Flats

“…In the sediment-water interface, articularly within the oxic zone, enhanced mineralization processes occur. Diagenetic reactions may partially redissolve the deposited materials into the porewater, from where diffusive fluxes, resulting from the concentration gradient at the sediment-water interface, may transport these dissolved contaminants from the sediments to the overlying water (Ciceri et al 1992;de Mora et al 2004). These kind of heavy metal fluxes in the sediment-water interface are particularly important in coastal areas with high productivity (Chase et al 2005).…”

Benthic Fluxes and Pore Water Profiles in the Tigullio Gulf

“…Diffusive fluxes at the sediment-water interface were computed applying the first Fick's law in the following form (Lermann and Brunskill, 1971;Ciceri et al, 1992):…”

“…More recently, the use of benthic chambers (Hall, 1984;Ciceri et al, 1992;Cambiaghi et al, 1993) allowed the direct measurements of benthic fluxes by taking into account the effect of bioturbation.…”