Cu speciation and cyanobacterial distribution in harbors subject to anthropogenic Cu inputs

Cu speciation was studied in four harbors on the south coast of Cape Cod, Massachusetts, that are exposed to varying degrees of Cu contamination from anthropogenic sources. Copper in waters outside the harbors was complexed by ~10 nM of very strong chelators, twofold higher than ambient Cu concentrations. In Eel Pond (Woods Hole) and Falmouth Inner Harbor, total dissolved Cu concentrations were 7-10-fold higher. However, because the strong chelators were saturated in these two harbors, the free Cu increased by 1,000-fold, from ~ 10^-13 M to ~ 10^-10 M. There was no evidence for any enhanced biological production of chelators in response to the elevated Cu concentrations. However, cell densities of cyanobacteria, which have been proposed as a source of strong Cu chelators in seawater, decline drastically in the high Cu harbors. These trends are consistent with culture studies showing that Synechococcus sp., the predominant cyanophyte in these waters, shows a dramatic decrease in growth rates above a free Cu²⁺ level of 10^-11 M. In Great Pond and Waquoit Bay, which showed no significant Cu contamination or saturation of strong ligands, cyanobacterial cell densities showed little or no decrease. Results suggest that significant anthropogenic inputs of Cu may overwhelm processes occurring in seawater that lead Cu and strong chelator concentrations to approach comparable levels.