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

This field study was a combined chemical and biological investigation of th e relative rates of weathering and biodegradation of oil spilled in sedimen ts and testing the influence of a bioremediation protocol. The aim of the c hemistry work presented here was to determine whether the bioremediation pr otocol affected the rate of penetration, dissipation or long-term retention of a medium range crude oil (Gippsland) and a Bunker C oil stranded in tro pical Rhizophora sp. mangrove and Halosarcia sp. salt marsh environments. P ermission 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 hydro carbons (THC) and for individual alkane markers using gas chromatography wi th 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 stati stical difference in initial oil concentrations, penetration of oil to dept h, or in the rates of oil dissipation between untreated oil and bioremediat ed oil in the mangrove plots. The salt marsh plots treated with the waxy Gi ppsland oil showed a faster rate of biodegradation of the oil in the biorem ediated plots. In this case only, the degradation rate significantly impact ed the mass balance of remaining oil. The Bunker C oil contained only minor amounts of highly degradable il-alkanes and bioremediation did not signifi cantly impact its rate of loss in the salt marsh sediments, At the end of e ach 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 di ssolution, with a lag-phase of 1-2 months before the start of microbial deg radation. (C) 2000 Elsevier Science Ltd. All rights reserved.