Salt-marsh areas as copper complexing ligand sources to estuarine and coastal systems

Dissolved copper levels, copper complexing capacities and conditional stability constants have been determined in the Tagus estuarine waters and one of the saltmarshes located in this estuary, the Rosario saltmarsh. Tagus estuarine waters show a constant and around 20 nM copper concentration during the estuarine mixing. Most of this copper is organically complexed by a strong ligand (L(1)) with a concentration that varies between 19 and 55 nM and a log K' between 14.14 and 15.75. In addition L(1)/Cu ratios are quite constants and close to 1 all through the estuary, indicating the same source. A second and weaker ligand (L(2)) was also detected in these waters in higher concentrations (36-368 nM) but with a lower log K' that varies between 12.06 and 13.13. The present work has demonstrated that salt-marsh areas are important and continuous sources of copper complexing ligands to the Tagus estuary. Noticeable, tidal induced transport continuously feed these waters with copper and ligands, mainly with the stronger one. This continuous input, together with the high residence times of this system results in a quite constant concentration along the salinity gradient. This input represents 95% of the ligand present in the estuary.