The application of a modified CLE-ACSV method to dissolved copper and iron speciation in the coastal marine environment

This dissertation presents the use of a modified competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) method using salicylaldoxime as the added competitive ligand for studies of dissolved (filtrate; <0.45 mum) copper (Cu) and iron (Fe) speciation in seawater. The method was modified with multiple analytical windows for a spatial and temporal study of dissolved Cu speciation in San Francisco Bay, California. Speciation results were incorporated into [C u*T ] versus [Cu2+] plots to evaluate the ambient ligand pool 'carrying capacity' and to predict the impacts of fluctuating dissolved Cu concentrations on Cu toxicity in the Bay. The method was further modified for analyzing dissolved Fe speciation in estuarine, coastal, and river plume samples from two coastal regions in the NE Pacific. Despite hydrological differences between regions, dissolved Fe concentrations were strongly correlated in all surface samples outside the estuary with only the stronger L1 ligand class concentrations. Speciation results were overlaid on leachable particulate Fe concentrations, indicating that dissolved Fe concentrations were 'capped' by the L1 ligand concentrations. A strong correlation between dissolved Fe and L1 ligand concentrations at dissolved Fe concentrations greater than 0.2 nM was further observed in both surface and subsurface samples analyzed for Fe speciation in the southeastern Bering Sea, Alaska. This relationship, as observed in this dissertation for both the Bering Sea and the coastal plume regions of the NE Pacific, also persisted when published speciation data sets from independent studies were included. In light of the capping effect of L1 on dissolved Fe concentrations despite large concentrations of leachable particulate Fe observed in this work, the seemingly ubiquitous nature of this relationship between dissolved Fe and L1 ligand concentrations suggests that L1 ligands play a governing role in the solubility and supply of dissolved Fe. The research conducted for this dissertation constitutes a substantial advancement in our understanding of the importance of ambient strong Cu and Fe-binding organic ligands in the biogeochemical cycling of these metals in the marine environment.