Peculiarities of fuel oil natural transformation in the strait of kerch polluted in november 2007 in consequence of tanker accident. Marine and Ocean ecosystems,
Résumé
The paper is devoted to the analysis of results of five-year field observations of self-cleaning process in the Strait of Kerch coastal zone polluted by fuel oil in November 2007 in consequence of the tanker “Volgoneft-139” accident. These studies included visual assessment, sampling and laboratory analysis of oil slicks, seawater and sediment cores. The analysis of samples were carried out with the use of thin layer and column chromatography, optical and gravimetric methods making possible to determine separately the concentrations of hydrocarbons and asphaltic substances as well as the presence of hydrocarbons of contemporary biological origin.
The results of the investigations show that the spill of heavy fuel oil composed mostly of macromolecular, non-volatile and insoluble substances hasn’t increased considerably the water pollution level during the first months after the accident. In winter 2007/2008 the concentrations of hydrocarbons were stably high: 0.19−0.22 mg/dm3. However such values have always been observed here because of intensive navigation and port activity. Nevertheless the notable augmentation of concentrations up to 0.34−0.60 mg/dm3 in summer 2008 and their relatively high levels during next two aestival seasons might be caused by natural destruction of oil slicks stranded on the shore.
In contrast to water column and bottom sediments, the coasts were hardly polluted by the spilled fuel oil. Even after the termination of clean-up operations, numerous weathered oil slicks were still present in certain sectors, especially on limestone blocks of the Tuzla dam. In the course of time an exponential decrease in their quantities and in the ratio between hydrocarbons and asphaltic components was revealed. The values of half-period of oil pollution natural transformation varied from one to two years. The highest activity of natural cleaning process was observed for the small pollutant traces stranded on the rocky substrate and sandy beaches exposed to the influence of fresh air, solar radiation, storm waves and surf action. On the northern windward coast of the Strait of Kerch influenced by shallow, low-salinity and highly bio-productive waters of the Sea of Azov the spilled fuel oil trends to disappear more rapidly than on its southern coast washed by the Black Sea.