| Abstract
| - The physical and kinetic speciation of Cu and Zn in threeimpacted marine estuaries was examined. Contrasts insources of metal-binding ligands, solution chemistry, andhydrologic forcing between and within the three study systems(Cape Fear River Estuary, North Carolina; Norfolk−Hampton Roads−Elizabeth River, Virginia; San Diego Bay,California) were exploited to enhance our understandingof Cu and Zn speciation. Trace metal-optimized tangential-flow ultrafiltration at 1 kDa nominal molecular weightlimit (NMWL) was used to fractionate <0.4 μm speciesinto colloidal and “dissolved” pools. Colloidal species ofdissolved organic matter (DOM) and copper were significantand often the dominant pools in each of the three studysystems. Characteristic colloidal fractions of both DOM andCu ranged from near 70% of <0.4 μm concentrations inCape Fear to 50% in San Diego Bay. Colloidal Cu and DOMwere strongly coupled, and variability in observed <0.4μm Cu concentrations was closely related to theconcentrations of colloidal-associated metal. Colloidalfractions were much smaller for Zn than that of Cu; rangingfrom 10−30% in Cape Fear to less than 5% in San DiegoBay, and no relationship to DOM was observed. Kineticseparations on Chelex resin revealed the presence of largenonlabile pools of Cu in each of the study systems, withthe highest fractions (70−100%) in Cape Fear and Norfolkand lowest (30−50%) in San Diego Bay. A closerelationship was observed between colloidal and nonlabileCu species, implying slow reactivity of colloidal-boundCu. The fraction of filterable Zn labile to Chelex averaged97%, 85%, and 60% in San Diego, Norfolk, and CapeFear, respectively. Anthropogenic Zn appeared almostexclusively in the <1 kDa fraction, while anthropogenicCu was distributed between dissolved and colloidal pools.Copper particle−partition coefficients (Kd) followed thetrend: San Diego ≫ Norfolk > Cape Fear and were inverselycorrelated with DOC concentrations. Colloid-basedpartition coefficients were significantly greater, in manycases an order of magnitude greater, than particle-basedpartition coefficients. The partitioning data suggest thepresence of metal-enriched bacterial-derived exudates and/or discrete metal phases in colloidal-sized particles inimpacted regions of these estuaries. The strong relationshipsobserved between Cu and DOC indicate that Cu partitioningbehavior over a range of estuarine environments maybe modeled effectively with a limited set of coefficients.Our measurements of metal lability and size distribution implythat the fraction of <0.4 μm Zn that is likely to bebioavailable is greater than that for Cu, especially inimpacted regions of the study systems.
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