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 x 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 10(13.9)-10(14.9) 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]T to [Cu2+] thus exhibit a seasonal pattern similar to that of algal productivity, suggesting that the Cu-complexing ligands are produced by algae.