Spatial distribution and composition of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and hopanes in superficial sediments of the coral reefs of the Persian Gulf, Iran

This study is the first quantitative report on petroleum biomarkers from the coral reefs systems of the Persian Gulf.120 reef surface sediment samples from ten fragile coral reef ecosystems were collected and analyzed for grain size, biogenic elements, elemental ratios, and petroleum biomarkers (n-alkanes, PAHs1 and Hopanes) to assess the sources and early diagenesis of sedimentary organic matter. The mean grain size of the reef sediments ranged from 13.56 to 37.11% (Clay), 26.92 to 51.73% (Sand) and 35.97 to 43.85% (Silt). TOC2 (3.35-9.72 mg.g(-1)) and TON3 (0.4-1.10 mg.g(-1)) were identified as influencing factors on the accumulation of petroleum hydrocarbons, whilst BC4 (1.08-3.28 mg.g(-1)) and TIN5 (0.13-0.86) did not exhibit any determining effect. Although BC and TIN demonstrated heterogeneous spatial distribution, TOC and TON indicated homogenous distribution with continually upward trend in concentration from the east to west ward of the Gulf. The mean calculated TOC/TN ratios vacillated according to the stations (p < 0.05) from 2.96 at Shidvar Island to 8.64 at Hengam Island. The high TOC/TN ratios were observed in the Hengam (8.64), Kharg (8.04) and Sid (6.29), respectively, suggesting a predominant marine origin. The mean concentrations of Sigma C(11-35)n-alkanes, Sigma 30 PAHs and Sigma 9Hopanes were found in the ranges of 385-937 mu g.g(-1)dw, (overall mean:590 mu g.g(-1)dw), 326-793 ng.g(-1)dw (499 ng.g-ldw), 88 to 568 ng.g(-1) d (258 ng.g(-1)dw), respectively. Higher concentrations of detected petroleum biomarkers in reef sediments were chiefly distributed near main industrial areas, Kharg, Lavan and Sid, whilst the lower concentrations were in Hormoz and Qeshm. In addition, one-way ANOVA(6) analysis demonstrated considerably significant differences (p < 0.05) among concentration of detected total petroleum hydrocarbons between most sampling locations. Some sampling sites especially Kharg, Lavan, Sid and Lark indicated higher concentration of n-alkanes due to the higher maintenance of organic matter by high clay content in the sediments. Furthermore, most sediment samples, except for Hormoz, Qeshm and Hengam showed an even carbon preference for n-alkanes which could be correlated to bacterial input. NPMDS7 analysis also demonstrated that among the congeners of petroleum biomarkers, n-C-12,n-C-14, n-C-16,n-C-18 and n-C-20 for n-alkanes, Phe(8) and Naph(9) along with their Alkyl homologues for PAHs (2-3 rings accounted for 60%) and C-30 alpha beta and C-29 alpha beta for Hopanes were discriminated from their other congeners in the whole study area. Our results based on the PCA(10) analysis and diagnostic indices of AHs(11) and PAHs along with ring classification of PAHs, in addition, the ubiquitous presence of UCM,(12) and Hopanes revealed that the main sources of the pollution were petroleum and petroleum combustion mainly from offshore oil exploration and extraction, discharge of pollutants from shipping activities. (C) 2017 Published by Elsevier Ltd.