Trace metals in the water column of the Vigo Ria: Offshore exchange in mid-winter conditions

Samples of dissolved and particulate trace metals were taken in January-February 1995 at four different stations through an axial transect in the water column of the Vigo Ria. Average dissolved metal concentrations were 72 ± 9 pM for Cd, 4.6 ± 1.9 nM for Cu, 24 ± 20 nM for Fe, 2.5 ± 1.3 nM for Ni, 650 ± 340 pM for Pb and 4.8 ± 2.2 nM for Zn. No important differences in dissolved concentrations between stations or trend with depth were observed. Average particulate metal concentrations were 0.24 ± 0.12 μg g−1 for Cd, 44 ± 21 μg g−1 for Cu, 33 ± 8 μg g−1 for Ni, 156 ± 112 μg g−1 for Pb and 167 ± 32 μg g−1 for Zn. Both dissolved and particulate concentrations are within ranges for other European Atlantic coastal areas. The ria-ocean metal exchange was also quantified following the LOICZ (Land-Ocean Interaction in the Coastal Zone) protocol for quasi-steady states in estuaries. The pattern obtained for this winter campaign shows four different types of metal budgets: (1) a null net exchange for Cd; (2) a net dissolved output to the ocean for Cu, Fe and Zn (1.5, 4.1 and 0.8 mmol s−1, respectively); (3) a net export for both dissolved (0.12 mmol s−1) and particulate (0.29 mmol s−1) Pb; and (4) a net accumulation of Ni in the ria, with a net incoming oceanic flux of 0.51 mmol s−1 of dissolved and 0.31 mmol s−1 of particulate metal.