Hydrocarbon sources in Kachemak Bay Sediments: Improved Discrimination by Specific Compound ∂¹³C Measurements

Dr. Susan M. Henrichs
Dr. Donald M. Schell
Ms. Tara Borland
Mr. Timothy Howe

Institute of Marine Science
School of Fisheries and Ocean Sciences
University of Alaska
P.O. Box 757220, Fairbanks, AK

Identification of sources of polycyclic aromatic hydrocarbons (PAH) in sediments is an important step in reducing anthropogenic contamination. Identifications based solely on the composition of PAH can be confounded by compositional changes during weathering and biodegradation. Stable isotopic composition of individual PAH offers an additional marker, which can aid in distinguishing sources and which may less susceptible to alteration. Sediment samples from the Kachemak Bay area were analyzed for both the concentrations and ∂¹³C of individual PAH. The major potential sources of PAH to the area were also analyzed to determine which ones were major contributors to the sediments.

To determine the stability of the ∂¹³C of PAH in crude and diesel oil, microbial degradation experiments using sediment from the Kachemak Bay area, with added North Slope crude, Cook Inlet crude, and diesel oils, were conducted over a one-year period. PAH concentrations decreased and their composition changed, but the ∂¹³C of individual PAH remained constant. Hence, ∂¹³C of individual PAH has excellent potential as a relatively stable indicator of their sources. Based on isotopic and compositional data, the PAH in Kachemak Bay sediments appear to have mixed sources. Combustion and coal sources are more consistent with the data than are petroleum sources for the sediment PAH.

This project was funded by a grant from NOAA/UNH Cooperative Institute for Coastal and Estuarine Environmental Technology, NOAA Grant Number NA97OR0338.

Photos — top right: China Poot Bay; middle left: Little Tutka Bay; bottom right: Sadie Cove. SFOS photos by Ann Knowlton. Click on any of the images for a larger view.