Free Cupric Ion Concentration and Cu(II) Speciation in a Eutrophic Lake

The free cupric ion concentrations, [Cu2+], in the water column of eutrophic Lake Greifen were evaluated by means of ligand exchange with catechol and cathodic stripping voltametry of the Cu-catechol complexes. Total dissolved Cu, [Cu]T, was in the range 0.5-2.8× 10-8 M, while [Cu2+] ranged from 10-16 to 10-14 M at different times and depths. These values of [Cu2+] are much lower than literature values for the open sea. Equilibrium models of titration data indicate the presence of very strong ligands with conditional stability constants of 1013.9-1014.9 and corresponding concentrations of 40-90 nM. Measured [Cu2+] was especially low during the algal bloom in spring and was higher in winter. p[Cu] and ratios of [Cu]Tto [Cu2+] thus exhibit a seasonal pattern similar to that of algal productivity, suggesting that the Cu-complexing ligands are produced by algae.