An analysis method for the sources and distribution of organic carbon in large river estuary graded sediments

Abstract

This invention discloses an analytical method for the source and distribution of organic carbon in graded sediments of a large river estuary. The method includes the following steps: S1, collecting surface sediment samples from several different locations in the river estuary, pre-treating them, and then freeze-drying them to obtain freeze-dried samples; S2, performing organic carbon and stable isotope analysis and lignin analysis on the freeze-dried samples to obtain the δ¹⁸O₅ of the samples. 13 The values ​​of C and Λ8 are calculated using a three-terminal component mixture model. 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments determines the source and distribution of organic carbon in the sediments. This invention establishes an index for indicating the source and distribution of sedimentary organic carbon in graded sediments of large river estuaries, which helps to study the fate of organic carbon in large river estuary sediments under the influence of hydrodynamics.

Description

Technical Field

[0001] This invention relates to the field of marine chemical analysis technology, and in particular to an analytical method for the source and distribution of organic carbon in graded sediments from river estuaries. Background Technology

[0002] The continental shelf marginal seas influenced by large rivers are important interfaces for land-sea interaction and major sedimentary sinks of terrestrial organic carbon (Bianchi and Allison, 2009). Although they account for less than 10% of the total global ocean area, they store more than 90% of terrestrial organic carbon. Terrestrial organic carbon undergoes deposition, transport, and transformation here, which has a significant impact on the global biogeochemical cycle of carbon.

[0003] During the transport of sedimentary organic carbon in river estuaries, it is affected by physical processes such as estuarine hydrodynamics, which causes hydrodynamic sorting of sediments based on their density and particle size. This results in the selective distribution of organic carbon on the sediments, controlling the spatial distribution pattern of sedimentary organic carbon and thus affecting the spatiotemporal distribution pattern of marine carbon reservoirs.

[0004] As the spatial distribution patterns of sedimentary organic carbon change, sedimentary organic carbon from different sources exhibits selective distribution and degradation characteristics. Fine particulate matter can be transported to farther locations and undergoes a longer degradation process; coarse particulate matter preferentially settles in estuarine areas, with a relatively shorter degradation process. Due to the different reactivity and other characteristics of organic carbon from different sources—for example, terrestrial vascular plant organic carbon is recalcitrant, while marine organic carbon is highly reactive—ultimately, estuarine hydrodynamic processes alter the fate of sedimentary organic carbon.

[0005] Numerous indicators can be used to trace the source of sedimentary organic carbon, such as the ratio of total organic carbon (TOC) to total nitrogen (TN) (TOC / TN, or C / N for short). The C / N ratio for marine algae is 4-8, for terrestrial soils it is 9-15, and for terrestrial vascular plants it is >15. Stable isotopic abundance of organic carbon (δ¹⁵) is also important. 13C TOC), marine C TOC is approximately -20‰, terrestrial soil C TOC is approximately -26‰, and vascular plant C TOC is approximately -28‰; lignin content, marine C TOC is 0, terrestrial lignin content is greater than 0, and the more terrestrial the source, the higher the content; the ratio of isoprene tetraether membrane lipids to methyl branched tetraether membrane lipids (BIT) can be used to indicate terrestrial soil source, marine BIT is 0, and terrestrial soil source BIT is 1.

[0006] However, in estuaries with strong hydrodynamic forces, clarifying the sources and composition of organic carbon in graded sediments is crucial for studying the marine carbon cycle. Currently, the indicators for identifying the sources of organic carbon in graded sediments are unclear, limiting the quantitative estimation of the sources of organic carbon in estuarine sediments under hydrodynamic influence. Therefore, establishing a method to quantitatively assess the sources and spatial distribution of organic carbon in sediments from strongly hydrodynamic estuaries, combining sediment grading with the sources of sedimentary organic carbon, is a technically worthwhile research area.

[0007] Currently, research on carbon reservoirs in river estuaries is a hot topic both domestically and internationally. Due to the influence of hydrodynamic conditions, the distribution and fate of organic carbon in estuarine sediments remains a significant scientific challenge, necessitating the screening of effective indicators to quantitatively assess the source and distribution of sedimentary organic carbon of different grain sizes. Therefore, there is an urgent need to develop an indicator for assessing the source and distribution of sedimentary organic carbon in graded sediments of large river estuaries. Summary of the Invention

[0008] This invention aims to overcome the shortcomings and deficiencies of existing technologies and provides an analytical method for the source and distribution of organic carbon in graded sediments of large river estuaries. This invention employs a sieve grading method to study characteristic indicators that effectively indicate the source of sedimentary organic carbon in each grain size. Furthermore, a three-end-member mixture model is used to quantitatively estimate the source and composition of organic carbon in each grain size at different stations. Finally, principal component analysis is used to verify the characteristic indicators and end-member model results, establishing an index for indicating the source and distribution of sedimentary organic carbon in graded sediments of large river estuaries. This method is helpful in studying the fate of organic carbon in large river estuary sediments under the influence of hydrodynamics.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] An analytical method for analyzing the source and distribution of organic carbon in graded sediments from large river estuaries includes the following steps:

[0011] S1. Collect surface sediment samples from the estuary of the river, perform pretreatment to obtain samples divided into 6 particle sizes: >250μm, 125-250μm, 63-125μm, 32-63μm, 20-32μm and <20μm, and then freeze-dry them to obtain freeze-dried samples.

[0012] S2. The freeze-dried samples were subjected to organic carbon and stable isotope analysis and lignin analysis to obtain the δ¹⁸O values ​​of the samples. 13 C 样品 and Λ 8，样品 The value is obtained by using the three-terminal hybrid model method, as shown in equations (1)-(3) below:

[0013] δ 13 C 海洋来源 ×f 海洋来源 +δ 13 C 陆地土壤 ×f 陆地土壤 +δ 13 C 陆地维管植物 ×f 陆地维管植物 =δ 13 C 样品 (1)

[0014] Λ 8，海洋来源 ×f 海洋来源 +Λ 8，陆地土壤 ×f 陆地土壤 +Λ 8，陆地维管植物 ×f 陆地维管植物 =Λ 8，样品 (2)

[0015] f 海洋来源 +f 陆地土壤 +f 陆地维管植物 =1 (3)

[0016] Among them, f 陆地维管植物 f 陆地土壤 and f 海洋来源 Representing OC 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments, δ in the mixing model 13 C 海洋来源 δ 13 C 陆地土壤 δ 13 C 陆地维管植物 Λ 8，海洋来源 Λ 8，陆地土壤 and Λ 8，陆地维管植物 The values ​​are shown in Table 1 below:

[0017] Table 1. δ values ​​of different components in the mixed model 13 C and Λ8 values

[0018] <![CDATA[δ 13 C(‰)]]> -26.3±2.96 -28.1±1.68 -20.0±1.00 <![CDATA[Λ8(mg 100mg -1 OC)]]> 1.64±0.89 6.00±5.22 0

[0019] The OC was calculated using a three-terminal hybrid model. 陆地维管植物 OC 陆地土壤 and OC 海洋来源The relative proportion of total organic carbon in sediments determines the source and distribution of organic carbon in sediments.

[0020] Preferably, the pretreatment steps in step (1) are as follows: the bottom in-situ seawater of the collected surface sediment sample is filtered with a glass fiber filter membrane, the sediment sample is fully dissolved with the filtered seawater to obtain a mixture of seawater and sediment, the mixture is separated to obtain samples of six particle sizes: >250μm, 125-250μm, 63-125μm, 32-63μm, 20-32μm and <20μm.

[0021] This invention utilizes SPSS software version 21 to analyze various parameters and indices (C / N, δ) of graded sediments. 13 C. Indicators such as lignin content and BIT are normalized by dimensionality reduction to eliminate the differences between indicators and transform multiple indicators into a few comprehensive indicators.

[0022] Further optimization involves filtering the bottom seawater in situ using a 0.7μm glass fiber membrane, resulting in a sediment mass concentration of 20-50 g / L in the mixture of seawater and sediment.

[0023] Preferably, the specific steps of the organic carbon and stable isotope analysis in step (2) are as follows: the freeze-dried sample is thoroughly ground, the carbonate in the sample is removed with hydrochloric acid, and the organic carbon content, total nitrogen content and stable carbon isotope composition in each grade of sample are analyzed by using an elemental analyzer connected in series with a stable isotope mass spectrometer.

[0024] Preferably, the specific steps of lignin analysis in step (2) are as follows: the content of lignin monomers is analyzed by alkaline copper oxide method, each particle size sediment sample is weighed, the sediment lignin is decomposed into lignin phenol by alkaline copper oxide method, and the lignin phenol content is analyzed by gas chromatography.

[0025] Preferably, the sampling depth of the surface layer in step (1) is 0-2 cm.

[0026] Preferably, the river estuary mentioned in step (1) is the Yangtze River estuary and its adjacent sea area.

[0027] Preferably, the step (1) of collecting surface sediment samples from several different locations at the mouth of the river specifically involves collecting surface sediment samples from 10-15 different stations at the mouth of the river.

[0028] Preferably, the freeze-drying conditions in step (1) are: a minimum operating temperature of -60°C and a minimum pressure of 1 mbar.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] This invention focuses on the Yangtze River Estuary and adjacent sea areas, which are strongly influenced by hydrodynamics. Samples were collected from different stations, and a sieving and grading method was used to study characteristic indicators that effectively indicate the source of sedimentary organic carbon in each grain size. Furthermore, a three-endmember mixture model was used to quantitatively estimate the source and composition of organic carbon in each grain size at different stations. Finally, principal component analysis was used to validate the characteristic indicators and endmember model results, establishing an index for indicating the source and distribution of sedimentary organic carbon in graded sediments of large river estuaries. This is helpful in studying the fate of organic carbon in river estuary sediments under hydrodynamic influence. Attached Figure Description

[0031] Figure 1 This is a map showing the sampling stations for sediment samples in Example 1. Figure 1 The middle arrow indicates the direction of the ocean current;

[0032] Figure 2 The vibrating sieve used in Example 1 to separate sediment samples of different particle sizes;

[0033] Figure 3 The mass percentage of different particle sizes in sediments from the Yangtze River Estuary and adjacent sea areas in Example 1;

[0034] Figure 4 The distribution characteristics of various parameters with grain size in sediments from the Yangtze River Estuary and adjacent sea areas in Example 1 are shown (OC% represents the percentage content of organic carbon, Λ8 represents the content of lignin, br-GDGTs represents the content of branched tetraether film lipids, and iso-GDGTs represents the content of isoprene tetraether film lipids).

[0035] Figure 5 This is a scatter plot of different parameters between different grain sizes of sediments from the Yangtze River Estuary and adjacent sea areas in Example 1 (marine represents the range of marine source endmember values, soil represents the range of terrestrial soil endmember values, and vascular plant represents the range of terrestrial vascular plant endmember values).

[0036] Figure 6 This is a quantitative estimation diagram of the source composition of organic carbon in sediments of the Yangtze River Estuary and adjacent sea areas calculated using a three-terminal-member mixing model in Example 1;

[0037] Figure 7 This diagram represents a quantitative estimation of the source composition of organic carbon in sediments of the Yangtze River Estuary and adjacent sea areas, calculated using principal component analysis. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are considered to be commercially available through conventional markets. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0039] The detection conditions for organic carbon and stable isotope analysis in the following examples are based on those described in Wang, J., Yao, P., Bianchi, TS., Li, D., Zhao, B., Cui, X., Pan, H., Zhang, T., Yu, Z., 2015. The effect of particle density on the sources, distribution, and degradation of sedimentary organic carbon in the Changjiang Estuary and adjacent shelf. Chem. Geol. 402, 52–67. The detection conditions for lignin analysis are based on those described in Hedges, JI, Ertel, JR, 1982. Characterization of lignin by gas capillary chromatography of cupric oxide oxidation products. Anal. Chem. 54, 174–178. Analysis of tetraether membrane lipids: The content of tetraether membrane lipids was analyzed by liquid chromatography-tandem time-of-flight mass spectrometry (LC-TFS). The reference was Becker, KW, Lipp, JS, Zhu, C., Liu, XL, Hinrichs, KU, 2013. An improved method for the analysis of archaeal and bacterial ether corelipids. Org. Geochem. 61, 34–44. The ratio of the content of isoprenoid tetraether membrane lipids to branched isoprenoid tetraether membrane lipids was referenced to Hopmans, EC, Weijers, JWH, Schefuβ, E., Herfort, L., Sinninghe Damsté, JS, Schouten, S., 2004. A novel proxy for terrestrial organic matter insediments based on branched and isoprenoid tetraether lipids. Earth Planet. Sci. Lett. 224, 107–116.

[0040] δ of terrestrial soils in Table 1 below 13C-values ​​are referenced from Zhang et al., 2007 (Zhang, J., Wu, Y., Jennerjahn, TC, Ittekkot, V., He, Q., 2007. Distribution of organic matter in the Changjiang (Yangtze River) Estuary and their stable carbon and nitrogen isotopic ratios: implications for source discrimination and sedimentary dynamics. Mar. Chem. 106, 111–126.), δ-values ​​for terrestrial vascular plants. 13 C-value referenced Yu Hao et al., 2007 (Yu Hao, Wu Ying, Zhang Jing, et al. Lignin characteristics of plants and soils in the Yangtze River Basin [J]. Journal of Environmental Science, 2007, 27(5):7), δ-values ​​from marine sources. 13 C values ​​are referenced from Zhang et al., 2007. Λ8 values ​​for terrestrial soils are referenced from Yu et al., 2007; Λ8 values ​​for terrestrial vascular plants are referenced from Yu et al., 2007; and Λ8 values ​​for marine sources are referenced from Yu et al., 2007.

[0041] An analytical method for analyzing the source and distribution of organic carbon in graded sediments from large river estuaries includes the following steps:

[0042] S1. Collect surface sediment samples (surface refers to a sampling depth of 0-2cm) from the river estuary. Filter the bottom layer (approximately 1m from the seabed sediments) of the collected surface sediment samples with a 0.7μm glass fiber membrane. Use the filtered seawater to fully dissolve the sediment samples, obtaining a mixture of seawater and sediment. The mass concentration of sediment in the mixture is 20-50g / L. Divide the mixture into six particle size fractions: >250μm, 125-250μm, 63-125μm, 32-63μm, 20-32μm, and <20μm. Then freeze-dry the samples (minimum operating temperature -60℃, minimum pressure 1mbar) to obtain freeze-dried samples.

[0043] S2. Perform organic carbon and stable isotope analysis, lignin analysis and tetraether membrane lipid analysis on the freeze-dried samples respectively.

[0044] The specific steps for organic carbon and stable isotope analysis are as follows: the freeze-dried sample is thoroughly ground, the carbonate in the sample is removed with hydrochloric acid, and then the organic carbon content, total nitrogen content and stable carbon isotope composition in each grade of sample are analyzed by using an elemental analyzer connected in series with a stable isotope mass spectrometer.

[0045] The specific steps for lignin analysis are as follows: The content of lignin monomers is analyzed using the alkaline copper oxide method. Separate samples of each particle size are weighed, and the lignin in the sediment is decomposed into lignin phenols using the alkaline copper oxide method. The content of lignin phenols is then analyzed using gas chromatography.

[0046] The specific steps for tetraether membrane lipid analysis are as follows: tetraether membrane lipids are extracted from freeze-dried fractionated samples using a mixed solvent of dichloromethane and methanol at a volume ratio of 1:2. The content of tetraether membrane lipids is then analyzed by liquid chromatography-tandem time-of-flight mass spectrometry. The BIT index is obtained by using the ratio between the content of isoprene tetraether membrane lipids and branched isoprene tetraether membrane lipids, which is used to indicate terrestrial soil input.

[0047] The δ¹⁸O values ​​of the sample were obtained through the above organic carbon and stable isotope analysis and lignin analysis. 13 C 样品 and Λ 8，样品 The value is obtained by using the three-terminal hybrid model method, as shown in equations (1)-(3) below:

[0048] δ 13 C 海洋来源 ×f 海洋来源 +δ 13 C 陆地土壤 ×f 陆地土壤 +δ 13 C 陆地维管植物 ×f 陆地维管植物 =δ 13 C 样品 (1)

[0049] Λ 8，海洋来源 ×f 海洋来源 +Λ 8，陆地土壤 ×f 陆地土壤 +Λ 8，陆地维管植物 ×f 陆地维管植物 =Λ 8，样品 (2)

[0050] f 海洋来源 +f 陆地土壤 +f 陆地维管植物 =1 (3)

[0051] Among them, f 陆地维管植物 f 陆地土壤 and f 海洋来源 Representing OC 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments, δ in the mixing model 13 C 海洋来源 δ 13 C 陆地土壤 δ 13 C 陆地维管植物 Λ 8，海洋来源Λ 8，陆地土壤 and Λ 8，陆地维管植物 The values ​​are shown in Table 1 below:

[0052] Table 1. δ¹⁸ Components in the Mixing Model of Sediments in the Yangtze Estuary 13 C and Λ8 values

[0053] <![CDATA[δ 13 C(‰)]]> -26.3±2.96 -28.1±1.68 -20.0±1.00 <![CDATA[Λ8(mg 100mg -1 OC)]]> 1.64±0.89 6.00±5.22 0

[0054] The OC was calculated using a three-terminal hybrid model. 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments determines the source and distribution of organic carbon in sediments.

[0055] In the following embodiments, it is preferred that the estuary of the river is the Yangtze River estuary and its adjacent sea area, and the surface sediment samples collected from several different locations in the estuary are specifically collected from 10-15 different stations in the estuary.

[0056] This invention utilizes SPSS software version 21 to analyze various parameters and indices (C / N, δ) of graded sediments. 13 C. Indicators such as lignin content and BIT are normalized by dimensionality reduction to eliminate the differences between indicators and transform multiple indicators into a few comprehensive indicators.

[0057] Example 1

[0058] This embodiment uses the Yangtze River Estuary and adjacent sea areas as the research target area.

[0059] An analytical method for analyzing the source and distribution of organic carbon in graded sediments from large river estuaries includes the following steps:

[0060] S1. Sample Collection: In August 2013, surface (0-2cm) sediment samples were collected from 11 stations in the Yangtze River Estuary. Figure 1 Based on the distance of the sample stations from the river mouth and the water depth at the stations, the stations were divided into stations near the river mouth (YZ6, YZ7, W04, W03 and W02) and stations far from the river mouth (A8-1, A9-3, A10-2, A11-1, A12-1 and A13-1). Among them, the stations near the river mouth were further divided into: Yangtze River Estuary stations YZ6 and YZ7, and Hangzhou Bay stations W04, W03 and W02.

[0061] Sample pretreatment: In-situ seawater from the bottom layer (approximately 1 m from the seabed sediments) at each station was filtered through a 0.7 μm glass fiber membrane. 40 g of sediment samples from each station were weighed and thoroughly dissolved in the filtered seawater from the corresponding station, using approximately 1 L of seawater per station, resulting in a seawater-sediment mixture. Then, stainless steel sieves with pore sizes of 250 μm, 125 μm, 63 μm, 32 μm, and 20 μm were placed sequentially from top to bottom on a vibrating sieve machine. Figure 2 The mixture of seawater and sediment is slowly poured (about 30 mL / min) from the top into a vibrating sieve to separate samples into six particle sizes: >250 μm, 125-250 μm, 63-125 μm, 32-63 μm, 20-32 μm and <20 μm. The wet samples are frozen and then freeze-dried.

[0062] S2. Perform organic carbon and stable isotope analysis, lignin analysis and tetraether membrane lipid analysis on the freeze-dried samples respectively.

[0063] The specific steps for organic carbon and stable isotope analysis are as follows: the freeze-dried sediment samples at each grade are thoroughly ground, the carbonates in each grade sample are removed with hydrochloric acid, and the organic carbon content, total nitrogen content and stable carbon isotope composition in each grade sample are analyzed by using an elemental analyzer connected in series with a stable isotope mass spectrometer.

[0064] The specific steps for lignin analysis are as follows: The lignin monomer content is analyzed using the alkaline copper oxide method. Approximately 1g of each particle size sediment sample is weighed, and the lignin in the sediment is decomposed into lignin phenols using the alkaline copper oxide method. The lignin phenol content is then analyzed using gas chromatography.

[0065] The specific steps for tetraether membrane lipid analysis are as follows: Weigh 1g of the freeze-dried fractionated sample, extract the tetraether membrane lipid with a mixed solvent of dichloromethane and methanol (1:2, v:v), and then analyze the content of the tetraether membrane lipid using liquid chromatography-tandem time-of-flight mass spectrometry. The BIT index is obtained by using the ratio between the content of isoprene tetraether membrane lipid and branched isoprene tetraether membrane lipid, which is used to indicate terrestrial soil input.

[0066] Based on the above analysis, the δ of the sample was obtained. 13 C 样品 and Λ 8，样品 The value is obtained by using the three-terminal mixture model method to calculate OC. 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments determines the source and distribution of organic carbon in sediments.

[0067] The experimental results are as follows:

[0068] The parameters of different particle sizes at various stations in the Yangtze River Estuary are shown in Table 2.

[0069] Table 2. Parameters at different particle sizes at various stations in the Yangtze River Estuary (“\” indicates no data)

[0070]

[0071]

[0072] The results of the three-terminal component hybrid models of different particle sizes at various stations in the Yangtze River Estuary are shown in Table 3.

[0073] Table 3 Results of three-terminal component hybrid models at different particle sizes at various stations in the Yangtze River Estuary (“\” indicates no data)

[0074]

[0075]

[0076]

[0077]

[0078] I. Quality distribution results of screening and grading: as shown in Table 2 and Figure 3 The results showed that particles smaller than 20 μm dominated sediments in the Yangtze River Estuary and adjacent sea areas. The proportion of particles smaller than 20 μm gradually increased from the Yangtze River Estuary to Hangzhou Bay and further away from the estuary. This indicates that particles larger than 20 μm had a high proportion near the Yangtze River Estuary and decreased as the distance from the Yangtze River Estuary increased. This suggests that different particle sizes underwent hydrodynamic sorting in the Yangtze River Estuary and adjacent sea areas.

[0079] II. Distribution results of different parameters in each particle size fraction after sieving and grading: (See Table 2 and...) Figure 4 The results showed that OC%, δ 13 C, br-GDGTs, and iso-GDGTs first decrease and then increase with increasing particle size. This indicates that organic carbon and its parameters are selectively distributed across different particle sizes. Lignin and BIT gradually increase with increasing particle size, suggesting that larger particle sizes contain greater contributions from terrestrial vascular plants and soil sources. In conclusion, due to the selective distribution of various indicators across different particle sizes, further screening of effective indicators is needed to effectively quantify the source and composition of organic carbon.

[0080] III. Screening Effective Indicator Combinations to Differentiate Organic Carbon Sources in Different Particle Sizes: As shown in Table 2, to further screen indicators that can effectively indicate the organic carbon sources in each particle size, a δ-index was established. 13 C vsC / N, δ 13 C vsBIT, δ13 C v.s. Λ8 scatter plot (as Figure 5 shown), it was found that Figure 5 δ in a 13 C v.s. C / N can effectively distinguish marine sources and soil sources, but has limited ability to distinguish vascular plants, and the parameters of different particle sizes overlap, resulting in unsatisfactory discrimination effects; Figure 5 δ in c 13 C v.s. BIT can effectively distinguish the parameter characteristics of different particle sizes and can effectively indicate the characteristics of organic carbon indicators from different sources at each particle size. However, the BIT parameter lacks effective end-member values and is difficult to quantitatively estimate; Figure 5 δ in b 13 C v.s. Λ8 can effectively distinguish each particle size with ideal discrimination effects, and the sources of different particle sizes show obvious differences. For example, the <20μm particle size is a mixed source of terrestrial soil and ocean, more from the ocean, while the >32μm particle size has more contributions from terrestrial vascular plants. Through the comparison of different index combinations above, it was determined that δ 13 C v.s. Λ8 is a relatively ideal index combination.

[0081] IV. Using Figure 5 the selected parameters in b and applying the measured values of the parameters in each particle size to the three-end-member mixing model, the contribution ratios of marine source, terrestrial vascular plant and terrestrial soil organic carbon were obtained. As shown in Table 3 and Figure 6 shown, in the small particle size, the contribution of marine source organic carbon dominates (more than 60%); as the particle size increases, the contribution of terrestrial source organic carbon gradually increases (reaching 60%), especially the contribution of terrestrial vascular plants. From the estuary to the stations far from the estuary, the contribution of vascular plant organic carbon decreases and the contribution of marine organic carbon increases. In the Hangzhou Bay, in the >32μm particle size, the contribution of terrestrial vascular plants is very high; in the stations far from the estuary, in the <20μm particle size, the marine contribution dominates absolutely.

[0082] V. To verify whether the selected δ 13 C v.s. Λ8 can effectively represent the overall true results. Using as comprehensive parameter indicators as possible (such as BIT, Λ8, total nitrogen / total organic carbon ratio, isoprenoid tetraether membrane lipids, branched tetraether membrane lipids, etc.) to ensure the display of the overall characteristics of the samples, and incorporating these parameters into the principal component analysis model for calculation, the results are as Figure 7 [[ID=3l]]shown, where Figure 7 a shows that multiple parameter indicators are also divided into 3 categories, namely terrestrial source, marine source and soil source. Figure 7Results showed that sediments of different grain sizes at each station were clustered into three main groups: Group 1, mainly composed of small-grained sediments from stations far from the estuary, with marine contribution being dominant; Group 3, mainly composed of coarse-grained sediments (32-63 μm and 63-125 μm) from Hangzhou Bay, primarily composed of terrestrial organic carbon dominated by vascular plants; and Group 2, mainly composed of a mixture of small-grained components (<20 μm and 20-32 μm) from Hangzhou Bay and large-grained components (>20 μm) from stations far from the estuary, indicating that the grain size in this group was mainly contributed by a mixture of marine and terrestrial sources. The results of principal component analysis were basically consistent with the results of the endmember mixing model proposed in this invention, fully demonstrating the effectiveness of the selected characteristic index (δ). 13 C and Λ8) can effectively represent the overall source contribution ratio of sediments, and fully demonstrate that this characteristic index can effectively distinguish the source, composition and distribution characteristics of sediment classification samples, and effectively indicate the hydrodynamic sorting results of organic carbon in strongly dynamic estuarine sediments.

[0083] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An analytical method for the source and distribution of organic carbon in graded sediments of large river estuaries, characterized in that, Includes the following steps: S1. Collect surface sediment samples from several different locations at the estuary of the river. Filter the bottom seawater of the collected surface sediment samples with a glass fiber filter membrane. Use the filtered seawater to fully dissolve the sediment samples to obtain a mixture of seawater and sediment. Separate the mixture using a vibrating sieve to obtain samples divided into six particle sizes: >250 μm, 125-250 μm, 63-125 μm, 32-63 μm, 20-32 μm, and <20 μm. Then freeze-dry the samples to obtain freeze-dried samples. S2. The freeze-dried samples were subjected to organic carbon, stable isotope, lignin, and tetraether membrane lipid analyses. The specific steps for organic carbon and stable isotope analysis were as follows: the freeze-dried samples were thoroughly ground, and carbonates were removed with hydrochloric acid. Then, a stable isotope mass spectrometer was used in conjunction with an elemental analyzer to analyze the organic carbon content, total nitrogen content, and stable carbon isotope composition of each grade of sample. The specific steps for lignin analysis were as follows: the lignin monomer content was analyzed using the alkaline copper oxide method. Separate sediment samples of each particle size were weighed, and the lignin in the sediment was decomposed into lignin phenols using the alkaline copper oxide method. The lignin phenol content was analyzed using gas chromatography. The δ¹⁸O₂ of the sample was obtained. 13 C 样品 and Λ 8，样品 The value is obtained by using the three-terminal hybrid model method, as shown in equations (1)-(3) below: delta 13 C 海洋来源 times f 海洋来源 plus delta 13 C 陆地土壤 times f 陆地土壤 plus delta 13 C 陆地维管植物 times f 陆地维管植物 equals delta 13 C 样品 (1) Λ 8，海洋来源 ×f 海洋来源 +Λ 8，陆地土壤 ×f 陆地土壤 +Λ 8，陆地维管植物 ×f 陆地维管植物 =Λ 8，样品 (2) f 海洋来源 +f 陆地土壤 +f 陆地维管植物 =1 (3) Among them, f 陆地维管植物 f 陆地土壤 and f 海洋来源 Representing OC 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments, δ in the mixing model 13 C 海洋来源 δ 13 C 陆地土壤 δ 13 C 陆地维管植物 Λ 8，海洋来源 Λ 8，陆地土壤 and Λ 8，陆地维管植物 The values ​​are shown in Table 1 below: Table 1 delta of different components in the mixture model 13 C and A8 values The OC was calculated using a three-terminal hybrid model. 陆地维管植物 OC 陆地土壤 and OC 海洋来源 The relative proportion of total organic carbon in sediments is used to determine the source and distribution of organic carbon in sediments; the specific steps of tetraether membrane lipid analysis are as follows: tetraether membrane lipids are extracted from freeze-dried fractionated samples using a 1:2 volume ratio of dichloromethane and methanol mixed solvent, followed by liquid chromatography-tandem time-of-flight mass spectrometry analysis of tetraether membrane lipid content. The BIT index is obtained by using the ratio between the content of isoprene tetraether membrane lipids and branched isoprene tetraether membrane lipids, which is used to indicate terrestrial soil input; the parameters BIT, Λ8, and δ are used to analyze the content of tetraether membrane lipids. 13 C. The total nitrogen / total organic carbon ratio, isoprene tetraether membrane lipids, and branched tetraether membrane lipids were included in the principal component analysis model for calculation. The principal component analysis results were compared with the three-terminal member mixture model to verify the δ-value. 13 C 样品 and Λ 8，样品 The value can effectively represent the overall contribution of the sediment source, thereby enabling the analysis of the source and distribution of organic carbon in graded sediments of large river estuaries.

2. The analytical method according to claim 1, characterized in that, The bottom in-situ seawater was filtered using a 0.7 μm glass fiber filter membrane, and the mass concentration of sediment in the mixture of seawater and sediment was 20-50 g / L.

3. The analytical method according to claim 1, characterized in that, The surface sampling depth mentioned in step (1) is 0-2cm.

4. The analytical method according to claim 1, characterized in that, The river estuary mentioned in step (1) refers to the Yangtze River estuary and its adjacent sea area.

5. The analytical method according to claim 1, characterized in that, Step (1) involves collecting surface sediment samples from several different locations at the mouth of the river, specifically collecting surface sediment samples from 10-15 different stations at the mouth of the river.

6. The analytical method according to claim 1, characterized in that, The freeze-drying conditions described in step (1) are: the minimum operating temperature is -60℃ and the minimum pressure is 1 mbar.

Images