Copper ion activity and concentrations of voltammetrically defined dis
solved, surface bound, and tightly bound colloidal copper in samples f
rom San Diego Bay were measured independently using potentiometric and
stripping voltammetric methods, respectively. 'Free' copper, calculat
ed from activity, was approximately three orders of magnitude less tha
n the concentrations of the dissolved, surface bound and tightly bound
copper fractions (indicating a high degree of complexation) and over-
all, was well correlated to them, suggesting a common, heterogeneous,
copper matrix, of probable organic nature, whose distribution is contr
olled by physical mixing. This finding supports the aggregate or 'onio
n' model of copper speciation in seawater. Within the bay, we also enc
ountered environments in which copper activity was not directly correl
ated to concentration and we attribute this to local production of org
anic ligands by microalgae.