River discharge of strong Cu-complexing ligands to South Atlantic Bight waters

Discharge of dissolved organic matter (DOM) provides an important source of strong Cu-complexing ligands to the coastal ocean waters of Long Bay off the southeast coast of North Carolina. Concentrations of strong Cu ligands (∑Li at fixed KCuL′=1013.5), measured using competitive ligand equilibration-cathodic stripping voltammetry with 8-hydroxyquinoline (8-HQ) as the competing ligand, were linearly correlated with dissolved organic carbon (DOC) concentrations (∑Li=0.23DOC−14, r2=0.81, p 0.01, n=9) in Long Bay transect samples. The relationship between ∑Li and DOC measured in this study was very similar to that measured in a previous study for Cape Fear estuarine sites. The Cape Fear provides 1.8×106 mol of strong Cu ligands annually to Long Bay with a ratio of ligand/DOC of 1.7×10−5 mol g−1 C. For South Atlantic Bight (SAB) shelf waters, yearly discharge from organic-rich rivers may provide up to 1.7×107 mol of strong Cu ligands. A river flux of this magnitude could support 1.6 nM strong Cu-complexation capacity throughout the SAB water column, or up to 50% of the total pool of strong Cu-complexing ligands. Estimates for the worldwide river discharge of terrestrial DOM indicate this source could support 0.03–0.2 nM strong Cu complexation capacity, or a maximum of 20% of the global ocean reservoir of strong Cu ligands.