Distribution Of Lignin In Mud Deposits Along The Eastern Coast Of Liaodong Peninsula And Its Indication To Terrestrial Organic Matter

The annual fluxes of particulate organic carbon and dissolved organic carbon into from rivers to ocean are 0.15×10¹⁵g and 0.25×10¹⁵g,respectively.Among them,90%of the terrestrial organic matter is stored in the estuary and the mud deposits in adjacent shelf.Therefore,it provides an ideal place for studying the source and distribution of organic matter and the source-sink process under the influence of human activities.C/N ratio??¹³C and biomarkers such as lignin are widely used to explore the source,migration and burial of organic carbon in estuaries and adjacent shelf.Among them,lignin exists only on land and except for some seaweeds,it has not been found to exist widely in marine organisms.At the same time,lignin has the advantages of rich content and diverse parameter information,so it is widely used to trace terrestrial organic matter.In this paper,the source,distribution and influencing factors of organic matter in sediment samples from the mud deposits along the eastern coast of Liaodong Peninsula were analyzed by C/N and?¹³C.Furthermore,according to lignin parameters,the proportion of terrestrial organic carbon buried in the total organic matter was explored.Also,lignin vegetation parameters were used to study the contribution of different vegetation types to terrestrial organic matter.With the help of lignin parameters,TOC content,C/N ratio,and?¹³C in core sediments,and by ²¹⁰Pb dating,the changes of organic matter content on a hundred-year time scale and the factors affecting its source,migration and burial were discussed.The main findings are as follows:?1?The C/N ratio and ?¹³C in the surface sediments of the mud deposits along the eastern caost of Liaodong Peninsula range from 6.50 to 12.80 and from-24.7‰to-22.0‰,respectively.And the lignin parametersand?8 are range from 0.1 to2.0mg/10gdw and from 0.1 to 3.0mg/100mg OC.The C/N ratio,and?8 all decrease with distance from the shore increasing,indicating that terrestrial organic matter gradually decreases from land to sea.?¹³C is slightly positive in the near-shore area,mainly affected by C4 plant input.?2?With end-member model,the proportion of terrestrial and marine organic matter in the sediments of the study area was quantitatively estimated according to?¹³C.The results showed that terrestrial organic matter content accounted for 29%-67%of the total organic matter in surface sediments,with an average of 43%;Otherwise,organic matter from marine algea accounted for 33%-70%,with the average of 57%,indicating that the organic matter in the study area is dominant by marine organic matter and mixed with terrestrial organic matter.The terrestrial organic matter mainly comes from the input of small and medium rivers nearby.?3?The lignin parameter S/V in the surface sediments ranges from 0.32 to 4.75with an average value of 1.59.And C/V ranges from 0.04 to 1.43 with an average value of 0.46.The LPVI ranges from 10 to 583,with an average value of 134.All three parameters indicated that the current vegetation type in the study area was dominated by angiosperm nonwoody and woody tissues,mixed with a few gymnosperm plants,which was consistent with the vegetation types in the Liaodong Peninsula now.?4?The C/N ratio and ?¹³C in core sediments Y1 and Y2 indicate that the organic matter is mainly from marine algea and mixed with terrestrial components.In core sediment Y1,before 1920,Liaodong Peninsula was in a natural state,with little interference from human activities.Therefore,the contribution of terrestrial and marine organic matter remained relatively stable.Overall,at this stage,the proportion of terrestrial and marine sources of organic matter is 52%and 48%,respectively.From1920 to present,the amount of marine organic matter in sediments has increased sharply while the terrestrial organic matter rapidly decreases due to the construction of reservoirs in the basin,with the average of both being 61%and 39%.In core sediment Y2,marine organic matter is dominant,with an average value of 66%.Specifically,it can be divided into three stages.Before 1780,the study area was in a natural state,and the proportion of marine and terrestrial organic matter did not change significantly.The average of both was 64%and 36%,respectively.From 1780 to 1880,under the influence of the Qing government's policy of allowing people entering northeast China,the population began to increase in Liaodong Peninsula and human activities intensified,resulting in an increasing trend of terrestrial organic matter,which was from 35%to39%.From 1880 to the present,due to the eutrophication of the coastal area caused by the construction of the port,the contribution from the marine organic matter in the sediments has increased significantly.?5?The source of lignin in core sediments Y1 and Y2 is mainly from angiosperm nonwoody tissues and mixed with gymnosperm and angiosperm woody tissues.Since 1800,as the temperature and precipitation in Liaodong Peninsula continued to increase,the vegetation type has evolved toward angiosperms.In addition,the lignin in the study area experienced a strong degree of degradation.