Sedimentary Geochemistry of Hydrocarbons from Narragansett Bay, Rhode Island: Incorporation, Distribution and Fate

Abstract

Determining the impact of petroleum pollution in estuarine environments is essential, due to their biological importance. The Marine Ecosystems Research Laboratory (MERL) offers a unique opportunity to investigate the geochemical fate and biological effects of chronic petroleum addition to the productive Narragansett Bay estuary. The two main objectives of this research were to determine: (1) the geochemical distribution of hydrocarbons for Bay sediments, and (2) the mode of incorporation, distribution and fate of saturated hydrocarbons in the MERL ecosystem sediments. The concentration of hydrocarbons (saturated, aromatic, biogenic, and anthropogenic) and chlorinated hydrocarbons (chlordane, DDT, and PCB’s) in mid-Narragansett Bay was determined to provide additional information on their geochemical distribution. Anthropogenic materials (chlordane, DDT, PCB’s and anthropogenic hydrocarbons) generally decrease with increasing depth in a core and reach background levels at depths consistent with the geochronology of this area of the Bay and the chronology of inputs of these materials. Bioganic materials (organic carbon and biogenic hydrocarbons) remained fairly constant with increased depth in a core. Size fractionation of two core sections showed more hydrocarbons (biogenic and anthropogenic) associated with the smaller size fraction (<45 >μm to >0.3 μm) in the surface core section, while the lower section had slightly higher concentration for these hydrocarbons in the larger size fraction (>45 μm). These results indicate that the input of biogenic materials to this sedimentary environment has remained fairly constant over the time period covered by this core, while the input of anthropogenic materials has increased dramatically. It appears that the increased input of anthropogenic organic materials, including hydrocarbons, to this estuarine environment, is reflected by increased concentration of these materials in the upper layers of the sediments. The second part of this investigation focused on the incorporation, distribution and fate of No. 2 fuel oil saturated hydrocarbons in sediments from the MERL ecosystems. Periodic additions of No. 2 fuel oil to the ecosystems simulated a chronic input. After the initial addition of oil, trace amounts were detected in the sediments within two weeks, but substantial accumulation was not seen until approximately 135 days after the initial chronic oil addition. The majority of the No. 2 fuel oil saturated hydrocarbons were found to be associated with suspended material in the water. Size fractionation of both suspended material and sediments indicated the No. 2 fuel oil saturated hydrocarbons associate to a larger extent with the smaller size fraction (~45 μm). Most of the