Date of Award
1989
Degree Type
Thesis
Degree Name
Master of Science in Oceanography
Department
Oceanography
First Advisor
John King
Abstract
The sediments of Narragansett Bay provide a record of historical as well as recent pollution input to the bay waters. In order to properly construct a history of metal contamination from a sediment core, it is first important to understand the present day sources and behavior of metal contaminants in the surface sediment. This approach justifies the organization of this thesis. The general chemistry, behavior and primary sources of trace metals in Narragansett Bay sediment is discussed first, and then the factors controlling the present day distribution of trace metals in the surface sediment are detailed. Combining the calculated sedimentation rates from each site with the downcore trace metal profiles allows for the construction of a historical metal contamination history for sediment from 9 different sites throughout Narragansett Bay. In addition, an attempt has been made to correct the trace metal data for both organic carbon and grain-size variations. The variation in organic carbon content between sites results in an almost negligible correction to the metals data, whereas a rather large grain-size correction is required for samples that contain large amounts of sand-size sediment.
Metal concentrations in recent surface sediment show exponential decreases with increasing distance away from the head of the Providence River. Copper has the highest concentrations with lead, chromium and cadmium following in decreasing order. Concentrations decrease along the length of the Providence River and drop substantially outside of the river mouth. This trend clearly illustrates that the upper Providence River is the dominant source of metal pollution to the bay. Several other sources outside of the river also input metals to the sediment including the Warren River, Newport Sewage Treatment Plant and the Quonset Point electroplating facility. Silver concentrations indicate that the entire upper bay sediment is contaminated relative to the lower bay. The Warren River, Mount Hope Bay and the Providence River are all contributing elevated levels of silver to the upper Bay sediment.
Sediment cores from the upper Providence River and Seekonk River reveal increasing trace metal concentrations (Cu, Pb, Cr, Ag, Cd) beginning in the early to mid 1800's. Municipal and industrial discharge are believed to be the sources of the contamination. Concentrations continue to increase to the present as a result of population and industrial growth. In general, metal contamination levels decrease downriver defining the upper Providence and Seekonk-Blackstone Rivers as the dominant sources of pollution input. Metal concentrations in the upper and mid bay do not begin increasing until the late 1800's, illustrating that the Providence area was the initial center of industrial growth. Metal profiles from Field's Point and Sabin Point illustrate that the Field's Point Waste Water Treatment Facility has had a profound effect on sediment metal contamination since 1900. Pawtuxet Cove sediment contamination levels are higher than typical mid Providence River sediment as the result of metal input along the length of the Pawtuxet River. Metal concentrations in Pawtuxet Cove sediment show metal concentrations increasing more rapidly near 1930, corresponding to a change in the nature of the Pawtuxet River industry at that time.
Apponaug Cove, Greenwich Bay and Calf Pasture Point comprise a suite of sites with varying metal contamination. Apponaug Cove sediment is the most contaminated as a result of the historical textile industry in the cove. Metal concentrations at all three site begin increasing near 1870 and all the sites appear to have been effected by the pollution from the Apponaug industry. Greenwich Bay and Calf Pasture Point sediment illustrate that additional sources of pollution including domestic sewage and road runoff have affected metal levels at these sites.
Grain size, magnetic susceptibility, water content, organic carbon and x-ray photographs all indicate that the upper contaminated sediment is lithologically different from the deeper sediment. Increased population and industrial growth and the accelerated clearance of land has altered the composition of sediment entering the bay.
Sedimentation rates are highest at the head of the Providence River (Fox Point = 3.75 cm/yr) with accumulation decreasing downriver (Sabin Point = 0.32 cm/yr). Comparison of our data with previous investigations shows that sedimentation rates can vary considerably within the upper bay as the result of circulation patterns. Apponaug Cove, Greenwich Bay and Calf Pasture Point represent sedimentation rates from the mid bay. Apponaug Cove appears to be trapping sediment more effectively than Greenwich Bay (0.51 and 0.35 cm/yr respectively), and Calf Pasture Point shows the lowest sedimentation rate (0.23 cm/yr). The similarity between sedimentation rates from Calf Pasture Point and Ohio Ledge (0.23 and 0.28 cm/yr respectively) suggests that sediment accumulation in the mid bay is more uniform than in the Providence River and upper bay.
Comparison of surface sediment metal concentrations in Narragansett Bay with values from other geographic locations defines the relative sediment quality in the bay. The Seekonk River and upper Providence River show extreme levels of trace metal contamination. Copper, lead and cadmium concentrations are several times higher than levels in Boston Harbor and Long Island Sound sediment, whereas chromium and silver levels are slightly lower. Mid-Providence River sediment (Sabin Point) is less contaminated, but metal concentrations are still similar to or higher than values in Boston Harbor and Long Island Sound. Metal contamination in the upper (Ohio Ledge) and mid bay (Calf Pasture Point) are much lower, similar to values in sediment from the Chesapeake Bay, with the exception that Ohio Ledge sediment shows rather high copper contamination.
Recommended Citation
Corbin, Jeffrey M., "RECENT AND HISTORICAL ACCUMULATION OF TRACE METAL CONTAMINANTS IN THE SEDIMENT OF NARRAGANSETT BAY, RHODE ISLAND" (1989). Open Access Master's Theses. Paper 2455.
https://digitalcommons.uri.edu/theses/2455