Date of Award
Doctor of Philosophy in Oceanography
John W. King
Many estuaries are degraded to some extent by anthropogenic activities which have released pollutants into waters entering or residing in these ecosystems. When organic chemicals and heavy metals enter the estuarine environment, contaminants rapidly become incorporated into the sediment, due to physical and chemical processes. Their subsequent behavior and mobility is influenced to a great extent by water column conditions and the geochemistry of the receiving sediments. Ultimately, the fate of contaminants in estuaries are decided by their transport and eventual burial. Objectives of this research were to (1) reconstruct the recent contaminant history of heavy metals and organic contaminants in the Taunton River estuary (2) study the transport and fate of PCB Aroclor 1268 in the river (3) evaluate the behavior of sediment-bound metals during periods of sediment resuspension.
A series of sediment cores were collected from along a transect in the Taunton River, a salt wedge estuary located in Narragansett Bay. Cores were dated using a combination of radiometric and non-radiometric techniques. Cores were analyzed for organic chemicals and heavy metals to reconstruct the spatial and temporal trends of contaminants in the river. Trends indicate that multiple sources of organic chemicals and heavy metals to the river existed, with contributions shifting over time. Heavy metals were the first contaminant to appear downcore, early in the nineteenth century, followed by PAHs. PCBs and pesticides appear at depths corresponding to their dates of introduction to the environment.
A specific PCB Aroclor, 1268 was identified and measured in each of the sediment cores. Using sediment core data and public records, dates of Aroclor 1268 discharge to the Taunton River were reconstructed. Dates of release to the river predated previously acknowledged dates of production and use of Aroclor 1268. The transport and burial of Aroclor 1268 was determined in each of the cores and from data compiled from other sources. Overall findings indicate that substantial levels of Aroclor 1268 are still present in surficial sediment more than fifty years after their discharge ceased.
To evaluate and model metal mobility during sediment resuspension events, formulated reference sediments with different physical and chemical characteristics were created and spiked with heavy metals. Field contaminated sediments were collected from sites around the United States and were used to compare and validate data from the reference sediments. Of all sediment characteristics evaluated, A VS was found to be the most effective variable in controlling metals release during short term resuspension events. Dissolved metals in AVS treatments were found to decline to trace levels when the AVS:metal molar ratio rose to, or exceeded one. Resuspension of the field sediments resulted in very little metal being released to the dissolved phase, regardless of AVS level, confirming the importance of other sediment binding phases in regulating metal release. Predictions of dissolved metal values in the field sediments were calculated based on their AVS:metal molar ratio. Comparison of predicted versus measured metals in the field sediments yielded mixed results, further reinforcing the importance of non-A VS binding phases in controlling dissolved metal release during non-equilibrium conditions.
In summary, the results of these studies further the understanding of sediment-bound contaminants in dynamic environments such as estuaries.
Cantwell, Mark G., "MOBILITY AND FATE OF CONTAMINANTS IN ESTUARINE ENVIRONMENTS" (2006). Open Access Dissertations. Paper 1583.