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

Abstract

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.