Metal composition and fluxes of sinking particles and post-depositional transformation in a ria coastal system (NW Iberian Peninsula)

The intra annual variation of the quantity and composition of the sinking particles in a ria coastal system (Vigo Ria, Galicia, NW Iberian Peninsula) has been studied. Levels of particulate metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, U, V and Zn) were determined both in the labile (1 M HCl extraction) and in the total fraction. The levels and type of metals found in different seasons of the year depended upon oceanographic, physical, chemical and biological conditions but, in general, lithogenic type metals (Al, Fe, Ti, U and V) were higher during winter rainy campaigns when high quantities of SPM were recovered in the trap. However, the more biogenic metals (Cu, Pb and Zn) followed a scattered variation. Vertical fluxes values varied within the following intervals: 0.4–6.1 g m− 2 d− 1 for Al, 0.7–7.6 μg m− 2 d− 1 for Cd, 0.1–0.6 mg m− 2 d− 1 for Co, 0.8–6.4 mg m− 2 d− 1 for Cr, 1.2–10.9 mg m− 2 d− 1 for Cu, 0.3–2.7 g m− 2 d− 1 for Fe, 1.8–19.8 mg m− 2 d− 1 for Mn, 0.5–2.9 mg m− 2 d− 1 for Ni, 1.7–7.9 mg m− 2 d− 1 for Pb, 0.1–0.2 g m− 2 d− 1 for Ti, 0.1–0.6 mg m− 2 d− 1 for U, 0.6–7.2 mg m− 2 d− 1 for V and 0.8–39.8 mg m− 2 d− 1 for Zn. In special, the deposited labile fraction is subject to postdepositional diagenetic processes with subsequent benthic fluxes of dissolved Cr, Cu, Mn, Ni, Pb and Zn form of the metals to the water column. For Co and Cd, however, their enrichment in the sediments compared to the traps suggests their association with a more refractory fraction upon postdepositional remineralization. This work represents one of the first studies about labile trace metal concentrations and intra annual variation in the particulate matter recovered from a sediment trap in a ria system.