The Distribution of Hydrocarbons in Narragansett Bay Sediment Cores

Abstract

To provide more extensive data on sedimentary hydrocarbons present in Narragansett Bay, twenty cores were collected and analyzed. The results confirmed some expected trends, and also revealed some unusual findings. There was a general decrease in surface sediment hydrocarbon concentration proceeding away from the Providence River toward the mouth of the Bay, and a decrease in hydrocarbon concentration with increasing depth in the sediment cores. However, the East and West Passages of the Bay were quantitatively different. A number of stations in the East Passage showed increasing hydrocarbon concentrations with depth in the cores. From available information, the exact cause of this phenomenon cannot be determined. However, the observed contamination could be due to one or a combination of the following: past Navy activities or unreported spills in that area, previous inputs from the Taunton River, or other factors. Organic carbon, total hydrocarbon/organic carbon percentages, the concentration of a biogenic hydrocarbon (HC344), and the percentage of HC344/organic carbon in surface sediments were measured and/or calculated to further the understanding of the transport of these substances throughout the Bay. The results indicate that organic carbon generally decreases with distance from the Providence River and with depth in the cores. However, some notable exceptions were found in the East Passage which corresponded to the high hydrocarbon concentrations with depth in these cores. There was a high correlation of total hydrocarbons with organic carbon for surface sediments throughout the Bay. Also, the HC/OC percentages generally decreased with increasing distance from the Providence River with depth in the cores, again with some exceptions in the East Passage. A high correlation of the HC344/OC percentage in surface sediments with distance down the Bay in the West Passage was observed while there was poor correlation in the East Passage. Finally, there was a poor correlation of HC344 vs the organic carbon in surface sediments for both the East and West Passages. The information from this study indicates that the main source of hydrocarbons in Narragansett Bay sediments is the Providence River, and that these compounds are probably introduced into the Bay proper via the tidal currents. Previous work has shown that the major source of hydrocarbons in the River is municipal sewage effluents (Van Vleet and Quinn, 1978). These workers have estimated also that approximately 51,000 tons hydrocarbons/year enter U.S. coastal waters via sewage effluents while approximately 25,000 tons/year enter through spills. The present study further