Geo-biological aspects of coastal oil pollution

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More than 10 years after the 1991 Gulf War oil spill on the Saudi-Arabian coast of the Arabian Gulf, natural remediation has only been partially successful. This fact demonstrates the importance of studying the preconditions for, and the process of, hydrocarbon degradation as well as the competing processes which prevent or slow them down. This paper deals with the preconditions of biodegradation: the presence of water, the availability of oxygen, the influence of temperature and the presence and type of degrading microorganisms. This paper discusses abiotic transformation as well as aerobic and anaerobic biodegradation. The importance of emulsification and hydrocarbon uptake into the degrading microorganisms is underlined. Competing processes include the conversion of liquid oil to viscous and finally solid material, the formation of solid sediment–oil mixtures and the clogging of sediment pores preventing oxygen from entering the pores. At first glance, the competing processes seem more “geological” while emulsification and hydrocarbon uptake seem more “biological”. However, since the necessary energy input (e.g., waves and turbulence) is “geo“(physical), it becomes clear, on the one hand, that the biological process requires geophysical energy input and, on the other hand, is inhibited by geological competition. Oil pollution as well as remediation progress affect the impacted environment since they leave undegradable residues and intermediates as well as microbial biomass and its conversion products. Sediments are enriched with organic matter, whose properties and behaviour are altered. Even inorganic matter may be formed during hydrocarbon biodegradation. The final part of this paper consists of case studies of the accident of the tanker BRAER (1993), the oil spill in the Arabian Gulf (1991), and the continual seeping of the wreck PRESTIGE (2002/03). These three cases demonstrate the importance of oil type, energy input, climatic conditions, as well as human interest in the use of the impacted coast, in determining speed and success of remediation and possible restoration measures.