Copper speciation in continental inputs to the Vigo Ria: Sewage discharges versus river fluxes

Continental inputs of copper via rivers and sewage into the Vigo Ria were evaluated. The main fluvial input is not contaminated and the most degraded discharges occur on the southern margin of the middle ria. Continental inputs of copper and ligands to the ria are dominated by sewage treatment plants (136 mol Cu day−1, 124 mol L day−1) supported by rivers (15 mol Cu day−1, 21 mol L day−1). The dissolved fraction is the main channel of discharge for rivers (66%) with particulate matter being predominant in sewage (63%). Dissolved copper is organically complexed both in rivers (99.8%) and sewage (99.9%). This minor difference may be attributed to the fact that the stability of sewage complexes is greater than those in rivers. Moreover, ligand concentrations are higher in sewage than in rivers. Thus, the natural continental inputs of copper and ligands into the ria are magnified by anthropogenic inputs (5–15 and 3–5 times higher for copper and ligands, respectively).