Fluxes of strong Cu-complexing ligands from sediments of an organic-rich estuary

Abstract

Benthic fluxes were evaluated as a source of strong Cu-complexing ligands ( K′ CuL>10 11) to the water column of the organic-rich Cape Fear River estuary along the North Carolina coast. A core incubation technique was used to measure sediment-water exchange of strong Cu-complexing ligands, as well as total dissolved Cu and dissolved organic carbon, at two sites within the estuary. Substantial ligand fluxes were observed only during summer experiments ( 850±610 nmol m −2 d −1 in June 2001 at lower estuarine site and 870±580 nmol m −2 d −1 in June 2002 at upper estuarine site). Strong ligand fluxes were correlated with DOC fluxes only for the June 2002 experiment. The ratio of strong Cu ligand:DOC fluxes among all cores from the June 2002 incubation ( 3×10 −5 mol g −1 C ) was nearly equivalent to the ratio measured in the water column in an earlier study of the Cape Fear estuary ( 2×10 −5 mol g −1 C ). Fluxes of TDCu were not statistically significant during any experiment and were not related to the behavior of strong Cu ligands. Although fluxes of strong Cu ligands were large during the summer months, short estuarine residence times (<1 week) and a large ambient water column pool of ligands (30–200 nM) limit the importance of sediment-water exchange as a major source to Cape Fear estuarine waters. However, the fluxing ligands are experimentally indistinguishable from those in the water column, suggesting that benthic fluxes may provide an important source to estuaries with long residence times or lower ambient ligand levels.