Processes controlling the geochemical cycling of strong copper-complexing ligands in estuarine and marine systems

Speciation data from Cape Fear estuarine transects show strong (log K ′_CuL > 1012) Cu-complexing ligands are conservatively mixed within this system and exist in substantial excess of dissolved copper levels (30–200 nM and <20 nM, respectively). River input of allochthonous DOM is the primary source of these complexants as evidenced by the excellent correlation between strong ligand and DOC concentrations (r2 = 0.93). Humic substances isolated using C₁₈ solid phase extraction may account for I00% of the strong Cu-complexation capacity in the Cape Fear. Collective discharge from organic-rich rivers along the southeast U.S. coast may contribute up to 43% of the strong ligand pool in shelf waters of the South Atlantic Bight.; Ultrafiltration analyses reveal most (58–94%) strong ligands exist as colloidal entities (>1000 Daltons) in the Cape Fear estuary. The relationship between strong ligand and DOC concentrations among size fractions is nearly equivalent to the relationship observed in estuarine transects.; Core incubation experiments show significant fluxes of strong Cu ligands out of the sediments only during summer months. Measured fluxes during June 2001 and June 2002 averaged 850 nmoles m−2 day −1 and 870 nmoles m−2 day−1 , respectively. The June 2002 flux was closely correlated with a coincident DOC flux, whereas results from June 2001 did not show a similar relationship. Fluxes of TDCu were small year-round.; Strong Cu ligands in filtered estuarine samples exposed to solar radiation degraded at a rate >20 times the photooxidation rate of the bulk DOM. Calculated first-order photodegradation rates based on a long-term irradiation experiment using a solar simulator accurately (within 25%) predicted the loss of strong ligand concentrations for estuarine samples exposed to natural sunlight.; Within the Cape Fear estuary, low primary productivity and short residence times do not allow for processes such as sediment-water exchange, photochemical degradation, and coagulation/deposition to significantly affect the geochemical cycling of organic Cu binding moieties. As a result, freshwater input of strong Cu-complexing substances from the Cape Fear River is balanced by the discharge of these binding agents to Long Bay.