Source And Distribution Of N-alkanes And Fatty Acids In Sediments From The Red Tide-frequent-occurrence Area In The East China Sea (ECS)

With the use of Gas chromatography-mass spectrometry (GC-MS), surface and core sediments samples of the red tide-frequent-occurrence area in the East China Sea (ECS) have been analyzed, in order to give a preliminary measurement of the content, composition, horizontal and vertical variation pattern of n-alkanes and fatty acids at the Yangtze River Estuary and its adjacent area, which is well known for its high-frequency occurrence of harmful algae bloom (HAB). Faced with huge quantities of parametric data, appropriate statistical method was successfully employed here, to elucidate the complex relationship between the organic matter compositions, content and relative environmental parameters. The results are listed as follows:1. A characterization study of lipid markers was undertaken to identify the provenance of the organic matter in surface sediments from the red tide-frequent-occurrence area in the East China Sea (ECS) from April to May of 2005 and 2006.During both sampling periods, Petroleum Hydrocarbon as revealed by the carbon preference index (CPI),ratio of Pr/Ph and relative abundance of n-C16 (n-C16%) or n-C18 (n-C18%), was a predominant component of the aliphatic hydrocarbons.Linear, branched, mono- and polyunsaturated fatty acids (FAs) from multiple organic matter sources, including microalgae, bacteria and vascular plant, were detected at all sites, which displayed no statistically significant difference between 2005 and 2006. The range concentration of total fatty acids was 0.0～5.56μg/g dw (dry weight) with higher percent to total fatty acids of the linear saturated fatty acids (LSFA) and lower percent of the branched saturated fatty acids (BrFA) and polyunsaturated fatty acids (PUFA). The composition and distribution of fatty acids (FAs) suggested the prominent contribution of microalgae and bacteria and the smaller of terrigenous inputs. In the red tide-frequent-occurrence area of the East China Sea (ECS), terrigenous fatty acids have higher concentration in nearshore coastal sediments especially at the Yangtze River Estuary, reflected freshwater input; while microalgae and bacterial fatty acids have higher concentration in offshore coastal sediments reflected marine input.2. Core sediments from the red tide-frequent-occurrence area in the East China Sea (ECS) have been analyzed to assess the sources and diagenesis of organic matter. One sampling site have been chosen: HB-8, which are located in the north of the East China Sea. Two lipid biomarkers composition were identified-----fatty acids and alkanes. With the contribution of seasonal variation organic matters and the degradation of bacteria and concentration of oxygen, the total content and composition of alkanes gradually decreased with increasing depth and increased at some depth,while fatty acids deceased rapidly from 0～41cm.Petroleum Hydrocarbon as revealed by the carbon preference index (CPI) and ratio of Pr/Ph, was a predominant component of the alkanes. From 0～4cm of core sediments, heavy petroleum hydrocarbons was the prominent contribution and below 4cm was light petroleum hydrocarbons.29 fatty acids were identified including linear, branched, mono- and polyunsaturated fatty acids which origined from different organisms included phytoplankton,bacteria and zooplankton of the marine ecosystem and vascular plant of the land. The concentration of total fatty acids was as high as 0.72μg/g dw (dry weight) in the upper zone which was much higher than that in the middle and bottom zones. The composition and distribution of fatty acids also suggested the prominent contribution of microalgae and bacteria of marine and the smaller of terrigenous inputs.In the surface sediment, the concentration of linear and branched fatty acids (LSFA, BrFA) was the highest, and in the top 27cm, showed a slight decrease with increasing depth. From 27cm to 41cm, the both fatty acids undergo two fluctuations with relatively high abundance and the lowest concentration was detected at 35cm and 27cm depth respectivelly. Unlike the distributions of linear or branched fatty acids (LSFA or BrFA), the unsaturated fatty acids showed a depth profile typical of rapid diagenetic reworking, with a sharp decrease: from 14cm to 41cm, the unsaturated fatty acids (UFA) remained at low abundance with no significant fluctuations. Their different depth profiles suggested that the linear or branched fatty acids (LSFA or BrFA) were more resistant to biodegradation than the unsaturated fatty acids (UFA).3. Lipid biomarkers (40 fatty acids and 25 alkanes) composition have been identified in surface sediments of the red tide-frequent-occurrence area and subjected to Principal Component Analysis (PCA) and Cluster Analysis (CA). The combination of lipid biomarkers and PCA proved a more sensitive indicator of sediment OM source than bulk elemental data. As different assemblages of sources and different diagenetic histories of alkanes and fatty acids, PCA separated 2 group sources of alkanes ( the heavy petroleum hydrocarbons and the light petroleum hydrocarbons ) and 3 group sources of fatty acids (algal-derived fatty acids,microbially-derived fatty acids,terrigenous fatty acids). Principal Component Analysis (PCA) of the bulk of alkanes data shows that the most significant organic matters source is the heavy petroleum hydrocarbons while the less important is the light petroleum hydrocarbons. The other results of PCA of the bulk of fatty acids data indicates that the largest contributor of fatty acids are the phytoplankton and bacteria in the marine ecosystem while the smallest is the terrigenous inputs.Cluster Analysis (CA) applied to 15 stations of surface sediments collected at the ECS. Results from CA have revealed that surface sediments collected at the ECS belong to tow groups: one influenced by allochthonous and autochthonous OM; the other by autochthonous OM.