A Preliminary Study On The Composition, Distribution And Source Apportionment Of Aliphatic And Polycyclic Aromatic Hydrocarbons In Surface Sediments From The South Yellow Sea And East China Sea

Continental shelf regions are the transition zones between continent and openocean and play a key role in the transport and storage of terrestrial organic materialsin the ocean. As two of the largest marginal seas in the Western Pacific Ocean, theYellow Sea （YS） and East China Sea （ECS） have attracted many concerns not onlybecause of their high primary productivity and high carbon burial rates, but also as aresult of the rapidly increasing environmental pressure of huge pollutant loadings onthe marine ecosystem. The studies on aliphatic hydrocarbons （AHs） and polycyclicaromatic hydrocarbons （PAHs） in the sediments are of important scientific andpractical significance in revealing the origins of sedimentary organic material andenvironmental pollution as well as their potential threat on marine organisms. In thisdissertation, we present systematic results on the composition characteristics, spatialdistribution patterns, and controlling mechanisms of multiple hydrocarbon biomarkers（n-alkanes, isoprenoid pristane and phytane, unresolved complex mixtures （UCM）,alkyl and parent PAHs） in surface sediments from the South Yellow Sea （SYS） andECS. The study aims to understand the origins of sedimentary organic material（SOM）, sediment contamination status by petroleum and PAHs, the sources andpotential ecological risk of PAHs in the study areas. The main conclusions aresummarized as follows:1. The content of total organic carbon （TOC） in the surface sediments from the SYSshowed an overall pattern of lower values near the coast and higher values in the mud area. The highest values occurred in the northeast part of the study area, and thelowest values were found off the Jiangsu coast. The average TOC content in thesamples from the ECS was relatively lower than that from the SYS. The highest levelappeared in the mud area to the southwest of Cheju Island while the lowest TOCcontent was found in the middle shelf, and higher level occurred in the inner shelfregion. The distribution pattern of TOC in the inner shelf was characterized byincreasing southward along the shoreline. In the study areas, the distribution of TOCis affected by many factors, such as sediment sources, grain-sizes, hydrodynamicconditions, and so on. The C/N ratio suggests that SOM in the SYS is derived fromboth terrestrial plants and marine organism. The terrestrial input dominates the sourceof organic material in the northern part of the study areas and Jiangsu coastal area,caused by inputs of materials from the modern Huanghe River and the old Huanghedelta, respectively. In comparison, the values of C/N in the ECS are lower than that inthe SYS. In coastal area, lower C/N ratios could be primarily attributed toanthropogenic influences, microorganism and soil-derived organic matter.2. Concentrations of n-alkanes （C14^C35） were from0.42to2.00μg·g^-1in the SYSsurface sediments and varied from0.36to1.79μg·g^-1in the ECS surface sediments,with mean values of1.01±0.34μg·g^-1and0.94±0.39μg·g^-1, respectively. In mostsamples, the n-alkanes had a bimodal distribution which is maximized at C16, C17orC18in the first mode and at C29or C31in the second mode. The short-chain （C14^C21）n-alkanes showed no noticeable even/odd preference, suggesting that microbialactivity or fossil inputs is the primary source. The profile of long-chain（C>25）n-alkanes with an elevated odd to even carbon preference revealed the occurrence ofprominent terrestrial inputs in the study area. Overall, bulk hydrocarbon parameterssuggest that SOM in surface sediment in the SYS is derived from both terrestrial andmarine sources, while that in the ECS is predominantly come from terrestrial sources.There is no significant correlation between the contents of n-alkanes and TOC%in thestudy areas, primarily because of the diversity of sources of n-alkanes.3. The presence of elevated levels of UCM and relatively low Pr/Ph ratios in mostsites revealed a petroleum contamination in the study areas, especially in the coastal areas of Jiangsu and south Zhejiang. With the exception of bacterial contribution, themajority of UCM is related to anthropogenic input of petroleum residues likely due tothe local river discharge and shipping activities. In addition, atmospheric deposition isprobably another important source for UCM.4. Concentrations of PAHs （TPAHs） varied from61to3601ng.g^-1in the SYSsurface sediments, with mean values of825±716ng.g^-1. TPAHs showed an overallpattern of lower values in the north part and higher values in the south part of the SYS.The highest values occurred in the northeast close to South Korea, could be likelyrelated to the ocean dumping, while the lowest values were found off the Jiangsucoast. The contents of TPAHs ranged from128to1643ng.g^-1in the ECS surfacesediments, with mean valus of771±411ng.g^-1. Among different sampling areas, thehighest level appeared in the inner shelf region while the lowest value was found inthe central shelf, and higher level occurred in the mud area to the southwest of ChejuIsland. PAHs concentrations in the study areas are at the low to moderate levels of theglobal range.5. TOC was identified as an important controlling factor in the TPAHs distributionin the SYS. However, the TPAHs distribution in the ECS was complicated byhydrodynamic condition, coastal pollutants discharge, black carbon （BC） andparticulate organic carbon （POC） in addition to TOC content. The distribution of theorganic carbon-normalized TPAHs in the SYS surface sediments revealed a clearspatial pattern, with high values near the coast and decreased values seaward, and thelowest values occurred in mud area in the central SYS.6.3ringed parent PAHs are the major components of TPAHs in most stations,accounting for64.1%±9.1%of them, followed by4ringed PAHs. Whereas thefraction of high （5to6） ringed PAHs presents as predominance in the mud area to thesouthwest of Cheju Island and central shelf, primarily caused by inputs of atmosphericdeposition. The main compounds of PAHs in the sediments are phenanthrene,fluoranthene, fluorene, methyl phenanthrene and pyrene, which are consistent withsources related to coal combustion.7. The results from diagnostic ratios and factor analysis indicate that domestic coal combustion and coking industry are the predominant sources of PAHs in the studyareas. The impact of wood combustion on the ECS is greater than that on the SYS,mainly related to the difference of energy usage and industrial structure betweenSouth and North China. In addition, natural gas combustion has been become animportant input for PAHs to the sediment of our study areas. Petrogenic source,compared with pyrogenic source, is a small contributor to the PAHs in surfacesediments of the study areas, primarily related to petroleum-derived PAHs are morevulnerable to degradation. The composition of PAHs sources in surface sediments isconsistent with the profiles of current Chinese energy consumption.8. To some extent, sedimentary PAHs have undergone weathering during long-rangtransport to the study areas. In addition to atmospheric deposition, the PAHs arepredominantly introduced into the SYS and the ECS coastal area via fluvial transport,while PAHs in surface sediments from the mud area to the southwest of Cheju Islandand central shelf are dominated by atmospheric deposition.9. The potential ecological risks of PAHs were evaluated on the basis of effectrang-low （ERL） and effect rang-median （ERM）. The results showed thatconcentrations of PAHs were much lower than ERM and the sediment had a lowprobability of ecological risk. However, contents of fluorene and phenanthreneexceeded the ERL value in many stations. They probably pose risks on the marinebenthos.