| Since The Industrial Revolution,under the influence of human activities,the flux of terrestrial organic carbon into the sea has constantly changed,which is of great significance for the development of the estuarine coast and the ecological environment evolution of the continental shelf.As an area with strong river-sea interaction,the source of organic matter in the muddy shelf of the continental shelf is not only a large number of terrestrial organic matter,but also provided by marine organic matter.In which the basin's terrestrial source input inverts the human activities in the basin,and the offshore ocean self-inversion retrieves the degree of eutrophication and productivity of the ocean.Therefore,the transport and burial of organic matter in muddy areas of continental shelf is of great significance for the study of the environmental evolution of the watershed.The muddy area is characterized by continuous sedimentation,enrichment of fine-grained materials,and stable sedimentary environment.Therefore,it is easy to adsorb organic matter and is a natural site for inversion of human activities in the basin and evolution of the marine environment.The muddy area of the Liaodong Peninsula is a typical muddy area formed by the action of small and medium-sized rivers.The human activities in the basin are complex and the human activities along the coast are intense.As a result,this area is also an ideal natural area for studying sediment records and inverting human activities.This paper analyzes the particle size,total carbon(TC),total nitrogen(TN),organic carbon(TOC),C/N ratio,and ?13C content of two columnar samples in the muddy area on the east coast of Liaodong Peninsula,and combines 210Pb dating results.Analyze the vertical distribution characteristics and correlation of each index,and determine the contribution of organic matter sources and organic matter from different sources through the end-member model.From the perspective of the history,how environmental indicators change with age and what impact human activities have on the burial distribution of organic matter.discuss.Research indicates:(1)The sediment composition of the Q02 column in the eastern part of the muddy area is dominated by silt and clay,with an average content of 67.05%and 26.91%,an average sand content of 6.04%,and an average grain size of 5.3-7.68 ?.The average value is 6.93 ?.The composition of the sediments in the Q04 column in the western part of the muddy area is dominated by silt,the average content is 62.11%,the average clay content is 15.74%,the average sand content is 22.15%,and the average grain size is between 4.97-6.56 ?.It is 5.78 ?.The environmental conditions of the two columns are different.The Q02 column is supplied more by the Yalu River and the coastal rivers,and the Q04 column is located in the island area where the water power is weak.The overall characteristics of the two columns are reduced from the bottom up to the coarse-grained material,reflecting the weakening of the upward momentum from bottom to top,which represents the sedimentary characteristics of the bottom rocky coast of the Liaodong Peninsula.(2)According to the CIC model,the deposition rate of Q02 in the eastern part of the muddy area is 0.39 cm·a-1,the deposition period is from 1766 to 2017,and the deposition rate of Q04 in the western part is 0.29 cm·a-1.The period was 1679-2017 The Q02 column is located in the muddy area near the mouth of the Yalu River,receiving more land-based material input,so the deposition rate is higher than the western Q04 column.(3)The organic matter content of the column sediments is subject to greater fluctuations due to the influence of sedimentary environment,hydrodynamic conditions,source input,and own productivity conditions in the study area.The TOC content of the Q02 column was between 0.41%and 1.24%,the average content was 0.63%,the TN content was between 0.039%and 0.135%,and the average content was 0.064%.After 1940,the contents of TOC and TN in sediments increased significantly,which had a good corresponding relationship with the smaller particle size and stronger adsorption capacity.The TOC content of the Q04 column was between 0.43%and 0.84%with an average content of 0.60%.The TN content was between 0.04%and 0.09%with an average content of 0.062%.The correlations between TOC and TN content in Q02 column and Q04 column were 0.9984 and 0.9968,respectively.Both showed good positive correlation and showed good fit with the sediment components.(4)The C/N value and ?13C content of Q02 column showed that the C/N value of A1 segment showed a downward trend from bottom to top,and the content of ?13C was higher,indicating that it was influenced by more sea-source materials or terrestrial C4 plants;The fluctuation of content is obvious,indicating the source of sea-land mixed material;the fluctuation of C/N value from bottom to top of A3 segment decreases,and the extreme value of low ?13C content appears at the bottom,indicating that the impact of land-source material is enhanced;the C/N value of A4 segment is not See significant changes,?13C content does not change much vertically.The ?13C content in the Q04 column increased from the bottom to the top in four stages,indicating that the impact from the sea source material increased.Section B1 indicates a stable sedimentary environment dominated by sea-source interaction;the ?13C content in B2 shows that the impact of land-sourced material gradually increases toward the direction of enhanced sea-source material influence from the bottom up;the C/N value fluctuation at B3 is smaller,?13C The content showed a downward trend,indicating the source of sea-land mixed material;the C/N value in the lower part of the B4 segment decreased significantly,and the lower,?13C content appeared a low extreme value,indicating that the seaborne material underneath this stage has a greater impact.(5)It is found that the impact of human activities on the input of terrigenous materials is reflected in two aspects,in conjunction with changes in particle size parameters and elemental geochemical indices.On the one hand,human development activities exacerbate the rate of soil erosion and increase the flux of rivers into the sea.For example,the increase in migrants,the management of timber by officials and merchants,the plunder of Japanese and Russian imperialists,and the policy of deforestation and wasteland reclamation have caused the destruction of the forest and grassland resources in the river basin.Increase the sediment content of the Yalu River;on the other hand,the construction of the reservoir reduces the flux of the river,weakens the hydrodynamic conditions of rivers entering the sea,and reduces the transport capacity,resulting in drastic changes in the water and sediment conditions,which makes surface adsorption in terrestrial materials transported by water bodies.More fine-grained materials account for more.(6)The human activities,environmental changes and sea level rise in the river basin resulted in the proportion of organic carbon sources in the two pillars being the characteristics of terrestrial sources decreasing the rise of sea resources,and reflecting the influence of different dominant factors in the eastern and western parts of the muddy area on the sea environment.The Q02 column in the east is mainly affected by environmental changes in the basin and sea areas.Wasteland,natural disasters,the Russo-Japanese War,railway construction and other events caused damage to the forestry resources and reduced vegetation cover.Since the 1940s,the construction of reservoirs has reduced the input of terrestrial organic carbon and sediment dating data.It is shown that the deposition rate of tidal flats on the west bank of the Yalu River has decreased by 90%since 1940.The western Q04 column is mainly affected by human activities along the coast and the eutrophication of the water body.The "Closure Restriction" policy has opened up restrictions on logging and mining activities in the northeast,resulting in a reduction in the forest cover rate.The construction of the port has also enabled the shipping activities in the northeastern region to become more frequent and increase the discharge to the sea;sea level since 1950 The rise has led to a gradual increase in the contribution rate of organic matter from sea sources.In recent years,pollutants from coastal industries and aquaculture activities have caused an increase in nutrients in water bodies,and the increase in marine algae has caused further deterioration of the marine environment. |
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