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Gladstone, Australia Field Studies: Weathering and Degradation of Hydrocarbons in Oiled Mangrove and Salt Marsh Sediments With and Without the Application of an Experimental Bioremediation Protocol |
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| Authors: | KA Burns S Codi NC Duke |
| Institution: | aAustralian Institute of Marine Science, P.O. Box 3, Townsville, Qld. 4810, Australia bMarine Botany Department, University of Queensland, St. Lucia, Qld. 4072, Australia |
| Abstract: | This field study was a combined chemical and biological investigation of the relative rates of weathering and biodegradation of oil spilled in sediments and testing the influence of a bioremediation protocol. The aim of the chemistry work presented here was to determine whether the bioremediation protocol affected the rate of penetration, dissipation or long-term retention of a medium range crude oil (Gippsland) and a Bunker C oil stranded in tropical Rhizophora sp. mangrove and Halosarcia sp. salt marsh environments. Permission for the planned oil spills was granted in the Port Authority area of Gladstone, Queensland (Australia). Sediment cores from three replicate plots of each treatment for mangroves and four replicate plots for the salt marsh (oil only and oil plus bioremediation) were analysed for total hydrocarbons (THC) and for individual alkane markers using gas chromatography with flame ionization detection (GC–FID). Sediments were collected at day 2, then 1, 2, 5 or 6 and 12 or 13 months post-spill for mangroves and day 2, 1, 3 and 9 months post-spill for salt marshes. Over this time, hydrocarbons in all of the oil treated plots decreased exponentially. There was no statistical difference in initial oil concentrations, penetration of oil to depth, or in the rates of oil dissipation between untreated oil and bioremediated oil in the mangrove plots. The salt marsh plots treated with the waxy Gippsland oil showed a faster rate of biodegradation of the oil in the bioremediated plots. In this case only, the degradation rate significantly impacted the mass balance of remaining oil. The Bunker C oil contained only minor amounts of highly degradable n-alkanes and bioremediation did not significantly impact its rate of loss in the salt marsh sediments. At the end of each experiment, there were still n-alkanes visible in the gas chromatograms of residual oils. Thus it was concluded that there was unlikely to be any change in the stable internal biomarkers of the oils over this time period. The predominant removal processes in both habitats were evaporation and dissolution, with a lag-phase of 1–2 months before the start of microbial degradation. |
| Keywords: | bioremediation oil spills mangroves salt marshes hydrocarbon weathering |
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