AN ENCLOSED ECOSYSTEM (MESOCOSM) EXPERIMENT ON THE FATE OF CRUDE OIL IN THE WATER COLUMN

Abstract

Marine oil spills account for a significant input of petroleum hydrocarbons into the marine environment, causing extensive damage to organisms and natural resources. Understanding the fate of spilled oil in the water column is fundamental to predicting the environmental impact of oil, and thus to developing effective response/restoration strategies. We studied the environmental fate of a simulated oil spill and the water-soluble fraction of Iranian Heavy crude oil using experimental 980 liter in situ mesocosm bags that mimic natural ecosystems. The replicated experimental treatments consist of unoiled control (？3), oil only (？3), and pre-mixed oil+dispersant (？3). The mesocosm experiment was conducted for up to 116 days (Apr. 17 to Aug. 10, 2009). The fate of artificially spilled crude oil in water column and the effect of dispersant application were monitored by measuring total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs) and their compositional changes with time. A much faster increase of oil concentration (TPH, PAHs, and alkylated homologues) in the water column was observed in the dispersant-treated oiled mesocosm than in the untreated oiled one by eight days after oil addition. Oil concentrations in the water column remained relatively stable thereafter, and the TPH levels in the ‥oil+dispersant… mesocosms were about two orders of magnitude higher than those in the ‥oil only… mesocosm. Depuration rates of TPH were also six times higher in the ‥oil+dispersant… mesocosm compared to those in the ‥oil only… group. Quantitative and compositional changes of oil components during the simulated weathering of crude oil were also recognized and compared between ‥oil only… and ‥oil+dispersant… treatments.