Dissolved trace metals found in natural waters may exist as free hydrated ions and as complexes with inorganic and organic ligands. In most natural waters, organic ligands form relatively strong complexes with these metals. Complexation of copper and zinc by organic ligands may impact the concentrations of the uncomplexed, free ionic forms of these metals which are assumed to be available to biota. The bioavailable forms of copper and zinc may be toxic to phytoplankton and benthic organisms and to the higher trophic levels which feed on these organisms.
The goals of this study are the following: (1) to determine quantitatively water column concentrations and benthic fluxes of total dissolved copper and zinc, dissolved copper- and zinccomplexing ligands, and ancillary parameters at two sites in the Cape Fear Estuary in North Carolina; (2) to determine the changes in cycling, fate, and organic speciation of dissolved copper and zinc that may occur during resuspension events, focusing on the role of photochemical reactions; and (3) to examine the effects of a large-scale dredging project on the speciation, fate, and cycling of copper and zinc in estuarine waters and sediments.
Sediment and water sampling will be conducted primarily at two sites, each of which are subject to shipping and berthing activities representative of Department of Defense (DoD) harbor facilities. Water column samples at the surface and near the bottom will be collected and filtered in the field using a clean pumping and filtration system. Benthic fluxes of total dissolved copper and zinc, dissolved copper- and zinc-complexing ligands, and dissolved organic carbon will be measured using a core incubation technique. Controlled photolysis experiments will be performed on estuarine water and on sediment suspensions.
Intercalibration samples were obtained from the Cape Fear Estuary and San Diego Bay and distributed to all copper/zinc project PIs for intercalibration of copper speciation techniques. Two preliminary experiments were completed in which Cape Fear estuarine water was exposed to ambient solar radiation to examine irradiation effects on copper speciation. The project team continued surveys of the Cape Fear Estuary to understand "baseline" conditions for metal speciation. A preliminary experiment was performed to determine benthic fluxes of copper and copper speciation in a marginal estuarine sediment. The project team met with researchers from the other two SERDP copper/zinc projects to plan collaborative efforts on intercalibration exercises and cooperative sampling efforts.
This project will quantify the contribution of benthic fluxes to the amount of complexed copper and zinc and of copper and zinc-complexing ligands in harbor waters. The effects of photochemistry on copper and zinc speciation in estuaries and harbors will be examined. The results can be used to develop scientifically-based water quality standards for copper and zinc in the aquatic environment. The data presented by this project will provide information on the potential amelioration of copper and zinc by dissolved organic ligands in harbors and estuaries. DoD can also use this data to evaluate water quality compliance criteria that are based on environmentally-relevant impacts of metal discharges and hence to ensure that economic resources devoted to environmental monitoring and compliance are most efficiently utilized.