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(243) Mass Balance and Speciation of Copper in San Diego Bay, California.
Chadwick, David*,1, Zirino, Alberto2, Rivera-Duarte, Ignacio1, 1 SPAWAR Systems Center San Diego, San Diego, CA, USA2 University of San Diego, San Diego, CA, USA
ABSTRACT- Copper is a ubiquitous contaminant in urbanized coastal harbors and bays, largely as a result of its use in anti-fouling coatings on boats and ships. In this study, we explored the mass balance and speciation of copper throughout San Diego Bay, using a one-dimensional model and a scale-matched field data set collected over several surveys between 2000-2002. We found that the overall distribution and fate of total copper in the waters of San Diego Bay can be explained by a balance between sources, tidal flushing and settling to the sediment bed. Model results that do not account for transport to the sediment bed tend to over-predict water column concentrations by up to a factor of about five. Tuning the model to provide a best fit to the measured water column distribution requires that roughly half of the total copper that enters the bay must be transported to the sediment, while the remaining half is flushed to the ocean. We also use the model and field data to explore the internal speciation of copper between particulate, dissolved-complexed, and free ion phases. This speciation is critical to the evaluation of potential exposure mechanisms and subsequent biological effects. The speciation results indicate that for most areas of the bay during most periods of the year, copper is likely to be highly complexed and unlikely to cause toxicity. An exception to this result appears to occur in restricted side basins with large numbers of boats, where the combination of strong sources and poor flushing tends to raise copper to levels at or above the natural complexation capacity of the bay water. Another exception appears to occur during certain seasonal conditions that result in extremely low particulate and organic matter levels in the bay, resulting in a strong shift in the free copper levels. This condition is of some interest because it appears to occur without any significant increase in the total copper concentrations.
Key words: copper, mass balance, San Diego Bay, modeling
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