Hydrocarbons emitted by human activities probably constitute the largest class of contaminants that are present in coastal areas, because of widespread use of fossil fuels for power generation and logistics, and accidental spillages. The chemical composition of hydrocarbon mixtures found in the marine environment allowed the identification of relative contributions of different natural and anthropogenic sources. Identification of these hydrocarbons, especially n-alkanes, could act as tracers for the possible sources. To evaluate n-alkanes concentrations with emphasis on source analysis, surface water without visible oil was collected from the cruise in April 2016. Determination and quantification were performed by solvent extraction and gas chromatography-mass spectrometry. Various molecular diagnostic parameters were used to assess the contribution of different sources and origin of n-alkanes in surface seawater of Jiaozhou Bay. Concentrations of total dissolved n-alkanes(C11-C37) were between 1.756-39.09 μg·L-1 with a high carbon number predominance profile without odd-even carbon number preference. The n-alkane concentrations varied spatially depending on the distance away from main input sources and the ability of water exchange. It was at a higher concentration in the northeast and west coastal areas, as well as the mouth of Jiaozhou Bay. And concentrations were relatively lower in the inner area and outside of Jiaozhou Bay. In the sea area with strong water exchange, concentrations of total n-alkanes were around 2.196 μg·L-1, which could be considered as the environmental background level of n-alkanes in Jiaozhou Bay. Those n-alkanes were dominated with C24, with a slightly odd carbon number preference in low carbon n-alkanes and an even carbon number preference in high carbon n-alkanes. The values of CPI for the whole range of n-alkanes series, low carbon n-alkanes, and high carbon n-alkanes were 0.949, 1.026, and 0.980, respectively. Diagnostic indices and curves indicated that the dominant inputs of those n-alkanes were from marine biogenic input such as algae and marine bacteria. The concentration profiles of n-alkanes in other areas were characterized by no odd-even predominance in the range of C21-C33 with peaks center at C24 which were indicative of anthropic contributions as emission sources. N-alkanes dominating with anthropic sources comprised a high proportion(83.7%) of total n-alkanes. Activities of harbors and ships were the main contributors of Jiaozhou Bay n-alkanes. Physical processes, such as evaporation and dilution, were the principal weathering mechanisms. Because of its sufficient environmental capacity, Jiaozhou Bay was still moderately contaminated with petroleum.
Keywords: Jiaozhou Bay; n-alkanes; pollution evaluation; source; surface seawater.