Recruitment of Benthic Animals as a Function of Petroleum Hydrocarbon Concentrations in the Sediment

Abstract

Three separate field installations, consisting of clean and oiled sediment in fiberglass trays, were placed in the intertidal zone of Sequim Bay, Washington, to determine rates of hydrocarbon depuration and recruitment of benthic organisms. Detailed chemical analysis, with glass capillary gas chromatography and gas chromatography–mass spectroscopy, were conducted such that individual compounds and hydrocarbon classes associated with the sediment after varying periods of field depuration could be quantitated. Depuration rates of hydrocarbon types in sediment receiving oil on the surface (installations I and II) decreased in the order of saturates, methylnaphthalenes, and methylphenanthrenes. Rates of specific compound and hydrocarbon class depuration followed the general pattern exhibited by total hydrocarbons (infrared analyses). In a period of 100 d, total hydrocarbons in surface-oiled, coarse sediments (I and II) decreased by 82–88%, while the amount in the finer substrate with mixed in oil (III) only decreased by about 21% and remained quite stable up to 290 d. The ratios of nC17/pristane and nC18/phytane were monitored for installations I and III (oil mixed with sediment). The ratios remained constant for a period of 4–6 mo and then dropped sharply, suggesting the presence of oil biodegradation. These results are discussed in relation to physical and chemical processes acting on the oil-contaminated sediments. Initial concentrations of oil in sediments upon field emplacement were about 5000–6000 ppm in installations I and II and approximately 700 ppm in installation III. At these concentrations, no substantial inhibition of recruitment by benthic organisms was observed. Future sampling of these populations and further analyses of all benthic organisms may provide a better evaluation of effects of specific hydrocarbon components in sediments on benthic recruitment. These results are discussed in light of oil spill studies and other field experiments. Key words: benthic organisms, gas chromatography, hydrocarbon, petroleum, sediment, spectroscopic techniques