Comparative Fate of Chemically Dispersed and Beached Crude Oil in Subtidal Sediments of the Arctic Nearshore

A three-year investigation was conducted to examine the incorporation of petroleum hydrocarbons (PHC) into subtidal sediments following experimental releases of oil during the Baffin Island Oil Spill(BIOS)Project experiments. The concentrations of PHC were determined by synchronous scanning UV/Fluorescence spectroscopy, while the composition of residual saturated and aromatic hydrocarbons was determined by gas chromatography and gas Chromatographie mass spectrometry. A pre-spill sampling and four post-spill samplings (one day, two weeks, one year and two years after the releases)were conducted in each testbay. After the surface release and beaching of non-dispersant treated oil(Bay 11),accumulation of PHC at levels of 1-10 μg·gˉ¹ was noted in subtidal sediments within two weeks.Concentrations steadily increased over the ensuing two years, so that two years after the release, up to 10% of the originally beached oil was present in subtidal sediments. Concentrations of up to 400 μg·gˉ¹ were detected in the shallow offshore sediments. All oil residues in surface sediment appeared to be confined to the top 0-2 cm of the sedimentcolumn. The eroding oil from the Bay 11 beach was compositionally quite heterogeneous, with weathered, biodegraded oil, as well as relatively unweathered oil, found on the beach and in the offshore sediments. Biodegradation of oil appeared to be restricted to the beached oil, with no significant degradation apparently occurring subtidally. After two years, the offshore oil residues still contained low molecular weight alkanes as well asalkylated naphthalenes. The situation in Bay 9, where chemically dispersed oil was discharged near the bottom, was quite different. In spite of a large water column exposure, the bottom sediments never contained more than 10 μg.gˉ¹ of oil. Of this amount of oil, asignificant fraction (20%) of the PHC was initially associated with the surface flocculent layer. Levels of oil in the Bay 9 sediments were on the order of 1 -3 μg.g¹ one year after the release. Sediment PHC levels in the other less exposed bays (Bays 10 and 7) never exceeded 3 μg.g ¹. /// Une enquête s'étendant sur trois ans a été menée afin d'examiner la pénétration d'hydrocarbures pétroliers (HCP) dans les sédiments situés en dessousdu niveau des marées, à la suite de déversements expérimentaux de pétrole durant les expériences du projet BIOS (projet de déversement de pétrole à l'île Baffin). Les concentrations de HCP ont été déterminées par sp