The Distribution Characteristics Of Lignin In Surface Sediments From The Bohai Sea And Adjacent Sea Area And Its Significance In Tracing Terrestrial Organic Matter

Estuarine systems and continental shelves act as a huge sediment trap to capture90%of terrestrial organic matters (TOMs) transported through rivers. Hence, researchon organic carbon in these areas is significant to understand marine sediment record,past primary productivity, remineralization efficiencies of organic matters, nutrientcycling in marine sediments and cycling of organic carbon in marine environment. Itis also the key to the question of the fate of TOMs in marine environment. Lignin hashigh chemical stability and the ability to resisting degradation. Moreover, lignin isunique to land vascular plants and is essentially absent from marine organisms. Thus,it is a good biomarker for TOMs and has been applied widely in the geochemistrystudy in soil, river, lake and marine environment.In this dissertation, the lignin parameters, δ13C and C/N of25surface sedimentsamples in the Bohai Sea and adjacent sea area were analyzed; the distribution patternof TOC, δ13C, C/N, the content of lignin Σ8and Λ8are discussed. The differencescaused by using different parameters and end-member models in the estimation of thecontribution of terrestrial organic carbon are preliminarily investigated. Informationon vegetation sources and degradation degree of terrestrial organic carbon areanalyzed according to S/V, C/V,(Ad/Al)V,(Ad/Al)Sand other parameters. Majorconclusions are as following:1. The content of organic carbon in the surface sediments from the Bohai Sea andadjacent sea area (TOC%) are0.12%~1.13%with an average value of0.45%. Thestation with the lowest value is at the estuary of the Yellow River, probably causedby the high load of sediment discharge with low organic carbon content from theYellow River. TOC%increases first and then decreases with increasing thedistance to the estuary in the estuarine areas of both the Yellow River and the Luanhe River. The content of total nitrogen (TN%), which is significantlycorrelated with TOC%(R2=0.95) and is almost unaffected by the content ofinorganic nitrogen, is between0.01%to0.16%with an average value of0.06%.2. C/N ratios in the surface sediments from the Bohai Sea and adjacent sea area are5.00to12.31, averaged at8.15. The low average value might be an indication thatthe main source of organic matter in the Bohai Sea and adjacent sea area is marinederived. δ13Cs of all the stations are-26.0‰~-22.1‰with an average of-23.1‰.Based on the two-end-member mixing model and δ13C, the contribution ofterrestrial organic carbon is estimated as30.67%to85.69%with an average of43.66%. The contribution of terrestrial organic carbon decreases with increasingdistance from the mouth in the Yellow River Delta, with a highest value observedat the station nearest to the mouth. In the estuarine area of Luanhe River, thecontribution of terrestrial organic carbon increases with increasing the distance tothe estuary followed by a decrease, which is similar to the pattern of TOC%. Therelatively higher contribution of terrestrial organic matter (to marine derivedorganic matter) in the southern part of the Bohai Strait indicates that there is alarge sedimentation area of TOMs in the central and southern area of the BohaiStrait. The grain size of the sediment in this area is small, which is beneficial tothe preservation of TOMs. In contrast, the eutrophication, the shallow water depth,the high primary productivity and other factors might contribute to the lower ratioof TOM inside the Bohai Bay area.3. The contents of lignin in sediments normalized to the total mass (Σ8) are0.08to0.35mg/10gds with an average of0.19mg/10gds. The Σ8in the estuarine areas ofboth the Yellow River and the Luanhe River increases first and then decrease withincreasing the distance to the estuary. A weak positive correlation betweenp-hydroxyphenyl monomers and total mass of11lignin phenols(TPL, mg/10gds)is witnessed(R2P=0.57), which may be attributed to the non-lignin sourcesignature of p-hydroxyphenyl phenols. The content of lignin normalized to thetotal organic matter (Λ8) is between0.10to2.52mg/100mgOC with an averagevalue of0.58mg/100mgOC. The Λ8value decreases with increasing distance off shore at the estuarine area of Yellow River. There is no significant correlationbetween Σ8and TOC%, neither between Λ8and TOC%, which indicates thatmarine derived organic matter is probably the major contributor to the organicmatter in the surface sediments in this area.4. Based on a two-end-member mixing model and Λ8values, the contribution ofterrestrial organic carbon are estimated as3.71%to93.33%with an average of21.59%, which is pronouncedly different from that obtained by δ13C. Thediscrepancy may be attributed to:(1) organic matters derived from riverorganisms reduced the proportion of lignin in TOM before being transported intomarine system, which interferes with the application of Λ8in estimating thecontribution of TOM;(2) Λ8of suspended particle matter in the Yellow Rivercould not represent the end-member value of all stations, while the choice ofend-member value remarkably affects the conclusion;(3) The complexhydrodynamics in Bohai Sea could affect the distribution of TOM in marineenvironment. Thus, it is difficult to give an accurate estimation of TOM by usingΛ8as a single proxy.5. Based on a combination of δ13C, C/N and Λ8, a three-end-member (vascular plant,soil organic matter and marine organism) mixing model was applied todetermine the source and contribution of terrestrial organic carbon. It is foundthat in the surface sediments from three stations in the estuarine of the YellowRiver, TOM accounts for36.54%to82.24%, soil organic matter contributes32.69%to70.09%, while vascular plants only account for3.85%to12.15%.Soil organic matter contributes85.23%to93.48%of TOM, which is much morethan that from vascular plants, and two-end-member mixing model mayunderestimate the contribution of terrestrial organic carbon.6. The S/V and C/V ratios are0.55~2.19and0.27~1.01in surface sediments ofBohai Sea and adjacent sea area, with average values of1.35and0.51,respectively. The general relationship between S/V and C/V reflects that lignin inthe surface sediments of Bohai Sea and adjacent sea area is mainly derived fromangiosperm and the non-woody tissues of gymnosperm. Moreover, LPVI, combined with S/V and C/V, suggested that TOM in surface sediments from theBohai Sea and adjacent sea area is a mixture of woody and non-woody tissues ofangiosperm and non-woody tissue of gymnosperm, with grass and leaves ofangiosperm being the major contributors.7. In all stations,(Ad/Al)Vvalues are between0.42to1.08with an average of0.67,while the (Ad/Al)Svalues are0.52to5.35with an average of1.49. All the(Ad/Al)Vand (Ad/Al)Svalues are higher than0.4, which indicates that lignin inthese stations has undergone high degree degradation.