WILL OCEAN ACIDIFICATION IMPACT METAL CONTAMINATED MARINE SEDIMENTS?

Atmospheric carbon dioxide concentrations have been increasing since the Industrial Revolution. Carbon dioxide is an acidic gas, and significant quantities of carbon dioxide have dissolved in the ocean, leading to a decrease in the pH of the ocean. The decreasing pH will change the speciation of metals, so ocean acidification may change the mobility and bioavailability of contaminant metals. In this study we aim to investigate if ocean acidification will enhance the release of metals from contaminated coastal sediments. Sediment cores from an urban estuary have been incubated at three pH levels, for over two months. Water samples have been collected for nutrients, dissolved iron and trace metal analysis to assess if the pH of the overlying water has an influence on the diffusive flux of contaminants from sediments. The sediments are incubated in duplicate at pH values of 7.2, 7.6 and control, representing the possible pH range estuarine sediments may experience within one hundred years. Preliminary results suggest there is no change in the phosphate flux from sediments between treatments. Analyses are continuing to determine if there is a change in the flux of other contaminants and to determine if there is a change in the depths of the redox zones due to acidification. Results of this experiment will provide new information on the long term fate of contaminated sediments in coastal waters.