A method for estimating the self-sourced dissolved organic carbon sink in freshwater rivers

Abstract

The present invention relates to a method for estimating the self-source soluble organic carbon sink of a freshwater river, comprising the following steps: collecting river water samples of freshwater rivers to obtain a spectrum of sample water bodies; modeling to obtain the main fluorescent groups in the water samples; comparative analysis to obtain the properties and sources of the fluorescent groups, and obtaining the divergent fluorescence intensity of the fluorescent groups; according to the properties of the fluorescent groups, selecting relevant standard samples to test the divergent intensity of the fluorescent groups of organic matter components of different concentrations, linear fitting modeling, and obtaining a linear fitting model; according to the linear fitting model, calculating the concentration of endogenous organic matter components in the downstream and upstream sections of the freshwater river section; combining the freshwater river flow data to calculate the self-source soluble organic carbon sink flux of the river section. The self-source soluble organic carbon sink statistical calculation method obtained by the present invention is fast and effective, can realize the identification of self-source organic carbon components in freshwater rivers, and is of great significance for summarizing and estimating the self-source organic carbon sink in terrestrial aquatic systems.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental geochemistry, and in particular relates to a method for estimating self-source soluble organic carbon sinks in freshwater rivers. Background Art

[0002] The global carbon leakage sink is 2.8Pg C / yr, accounting for 2.8Pg C / yr of annual CO 2 The karst carbon sink is considered to be a very important "missing sink". The karst carbon sink estimated by using the DIC dynamic balance in karst aquatic systems is 0.2-0.7Pg C / yr, accounting for 7-25% of the global missed sink. However, some scholars believe that the precipitation of CO by calcium carbonate in karst aquatic systems 2 will still be released into the atmosphere as HCO 3 - and CO 3 2- The karst carbon sink in the karst aquatic system is not stable. Liu Zaihua et al. believed that DIC exists in the karst aquatic system in a dynamic equilibrium form, and its content increases with time and space, which is a dynamic equilibrium inorganic carbon sink; at the same time, aquatic plants in karst water bodies can also convert DIC into organic carbon, and finally bury it in river and lake sediments as an organic carbon sink. In addition, the content of DOC in karst water bodies reaches more than 60% of the organic carbon content of water bodies, of which the refractory dissolved organic carbon (RDOC) accounts for 63%-88%, which is an important component of the karst organic carbon sink. However, the organic carbon in the karst surface aquatic system is composed of multiple sources such as soil organic carbon, terrestrial plants, aquatic plants, and water microorganisms. Therefore, the quantitative evaluation of self-sourced / exogenous organic carbon in karst water bodies is relatively complicated.

[0003] Existing studies have divided the total organic carbon (TOC) in water bodies into solid particulate organic carbon (POC, with a diameter greater than 0.7um) and soluble organic carbon (DOC, with a diameter less than 0.7um) for research. It is generally believed that POC forms river or lake sediments and becomes a stable carbon sink. End-member mixing calculations based on isotope and geochemical stoichiometry found that the endogenous POC content in the Zengjiang River Basin accounted for more than 70-80%, while the endogenous POC content in the Mississippi River Basin was 52-61%. In water bodies, the proportion of DOC and POC is related to the turbidity of the water body. In clear karst water, the DOC content can reach more than 80%. The self-source DOC in karst water bodies calculated with aquatic plants, soil and terrestrial plants as mixed end members also reached more than 80%. However, most of the existing self-source DOC estimates are based on the component composition of homologous POC, rather than directly analyzing the endogenous and exogenous components and their contents of water body DOC. Therefore, the existing endogenous DOC estimates need to be further corrected.

[0004] Zhao Haijuan et al., Sun et al. used the stable isotopes of organic matter and the C / N ratio to calculate the source and proportion of organic matter. However, due to the limitations of sampling and testing technology, they used homologous particulate organic matter (POC) to calculate the proportion of soluble organic matter (DOC) components, rather than directly using the source components of soluble organic matter in the water body for calibration. The contents of different components in POC and DOC vary, so the results calculated using POC components may be different. Yang et al. used the components of fatty acids in water to calculate the content of DOC components, but the content of fatty acids in nature only accounts for about 20% of the total organic matter in water bodies, and there are errors in using the characteristics of some substances to refer to the total DOC. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for estimating the self-sourced soluble organic carbon sink of a freshwater river.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0007] A method for estimating the self-sourced dissolved organic carbon sink of a freshwater river is provided, comprising the following steps:

[0008] S1. Collect river water samples from downstream and upstream sections of freshwater rivers, scan and analyze to obtain three-dimensional fluorescence EEM spectra of sample water bodies; use parallel factor analysis to model and obtain the main fluorescent groups in water samples;

[0009] S2, comparing the excitation and emission spectra of the fluorescent group with the components in the OpenFluor database to obtain the properties and sources of the fluorescent group and obtain the divergent fluorescence intensity of the fluorescent group;

[0010] S3. According to the properties of the fluorescent group, relevant standard samples are selected to test the divergence intensity of the fluorescent group of organic matter components with different concentrations, and linear fitting model is established to obtain a linear fitting model;

[0011] S4. Calculate the concentration of endogenous organic matter components in the downstream and upstream sections of freshwater river sections based on the linear fitting model;

[0012] S5. Calculate the self-sourced dissolved organic carbon sink flux of the river section based on freshwater river flow data.

[0013] Furthermore, in step S3, the linear fitting model is y=ax+b, wherein y is the concentration of the organic component; x is the emission intensity of the fluorescent group; and a and b are linear fitting constants.

[0014] Furthermore, the specific method of step S5 includes the following sub-steps:

[0015] According to the formula:

[0016] F i =Q i *C i

[0017] Obtain the self-sourced dissolved organic carbon sink flux F at different river sections i ; where i is up or down; Q i is the flow rate at the river section i, C i is the concentration of self-source organic matter at river section i;

[0018] According to the formula:

[0019] ΔF=F down -F up

[0020] Obtain the self-source dissolved organic carbon flux of the river section ΔF; where F down and F up They are the self-source dissolved organic carbon sink flux in the downstream and upstream sections of the river section.

[0021] The beneficial effects of the present invention are:

[0022] The present invention inverts the components and properties of soluble organic carbon by analyzing the fluorescence spectral properties of colored soluble organic carbon in water, calculates the concentration of self-sourced soluble organic carbon components, and realizes the flux estimation of self-sourced soluble organic carbon sink in combination with river flow. The self-sourced soluble organic carbon sink statistical calculation method obtained by the present invention is fast and effective, and can realize the identification of self-sourced organic carbon components in freshwater rivers, which is of great significance for summarizing and estimating self-sourced organic carbon sinks in terrestrial aquatic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The EEM fluorescence spectrum component diagram of a water sample provided by an embodiment of the present invention; wherein: a, component 1 spectral position; b, component 2 spectral position; c, component 3 spectral position; d, component 1 half-test; e, component 2 half-test; e, component 3 half-test;

[0024] Figure 2 This is a regression diagram of the correlation between the fluorescence component intensity and the component organic carbon concentration of the standard substance provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0026] Example

[0027] A method for estimating the self-sourced dissolved organic carbon sink of a freshwater river comprises the following steps:

[0028] (1) Twenty-four groups of water samples were collected from six sampling points in the downstream and upstream sections of the Lijiang River. The three-dimensional fluorescence EEM spectra of the Lijiang River water samples were obtained by scanning and analysis. The parallel factor analysis method (PARAFAC) modeling was used to obtain the three main fluorescent groups in the Lijiang River water samples ( Figure 1 ). The split-half test showed that the Ex and Em peaks did not overlap, and the test passed, indicating that the three main fluorescent groups were independent components.

[0029] In an embodiment of the present invention, the fluorescence spectra of water samples and CDOM standard products use 3D-EEM fluorescence spectroscopy, and the water samples are filtered through a 0.7um glass fiber membrane filter after burning and scanned on the machine. Fluorescence spectra use a Shimadzu RF-5301PC fluorescence spectrophotometer (150W xenon lamp) in Japan, with a scanning excitation wavelength of 220-500nm and a divergence wavelength of 250-600nm, a scanning interval of 5nm, and are performed at room temperature (25°C). Liquid Rayleigh scattering uses ultrapure water (Millipore, ultrapure water system) as a comparison to deduct blank removal (excitation wavelength 348nm, divergence wavelength 395nm). The divergent fluorescence intensity is standardized using a specific excitation wavelength intensity.

[0030] EEMs ​​were analyzed by parallel factor analysis (PARAFAC) to identify the number, type, and intensity of DOM fluorophores. The excitation and emission spectra of the components that control the fluorescent EEMs and the concentration fraction of the fluorescent components proportional to the concentration of the fluorescent components were obtained by PARAFAC modeling. The dynamic changes of the concentration fraction provided a quantitative basis for monitoring the changes in the concentration of the fluorescent components obtained in the PARAFAC model. PARAFAC analysis used the N-way PARAFAC model (Andersson and Bro, 2000) of the Matlab toolbox (Matlab 6.5); the toolbox is available at http: / / www.models.kvl.dk / source / nwaytoolbox / (July 2010).

[0031] (2) The excitation and emission spectra of the fluorescent groups were compared with the components in the OpenFluor database (www.openfluor.org), and the main components and sources of the fluorescent groups were distinguished according to the principle of peak shape and peak position correspondence (Murphy, 2014) (Table 1), and the divergent fluorescence intensity of the three fluorescent groups was obtained (Table 2). According to the source and properties of the components, components C1 and C3 were determined to be self-sourced organic matter components, and component C2 was an exogenous terrestrial input component.

[0032] Table 1 Characteristics of three fluorescent components analyzed by EEM-PARAFAC

[0033]

[0034] Table 2 Fluorescence intensity and proportion of fluorescent groups

[0035]

[0036] (3) According to the three main fluorescent group components, glycine and fulvic acid standards were purchased, the fluorescent group divergence intensity of organic matter components with different concentrations was tested, and linear fitting modeling was performed to obtain the linear fitting model ( Figure 2 ). According to the linear fitting model, the divergent spectrum concentration of the fluorescent group in Table 2 was entered to calculate the content of organic matter components in the downstream and upstream sections of the river section (Table 3).

[0037] The linear fitting model is y=ax+b

[0038] y is the concentration of organic matter components; x is the emission intensity of the fluorescent group; a and b are linear fitting constants.

[0039] Among them, organic matter from aquatic plants and microorganisms is the self-sourced organic matter in the water body.

[0040] Table 3 Calculation of DOC component concentrations

[0041]

[0042] (4) Calculate the self-source carbon sink of the river section based on the flow data of different seasons (Table 4). The calculation method is as follows:

[0043] According to the formula:

[0044] F i =Q i *C i

[0045] Obtain the self-sourced dissolved organic carbon sink flux F at different river sections i ; where i is up or down; Q i is the flow rate at the river section i, C i is the concentration of self-source organic matter at river section i.

[0046] According to the formula:

[0047] ΔF=F down -F up

[0048] Obtain the self-source dissolved organic carbon flux of a river section ΔF; where F down and F upThey are the self-source dissolved organic carbon sink flux in the downstream and upstream sections of the river section.

[0049] Table 4 Estimation of self-source DOC carbon sink

[0050]

[0051]

[0052] The present invention inverts the components and properties of soluble organic carbon by analyzing the fluorescence spectral properties of colored soluble organic carbon in water, calculates the concentration of self-sourced soluble organic carbon components, and realizes the flux estimation of self-sourced soluble organic carbon sink in combination with river flow. The self-sourced soluble organic carbon sink statistical calculation method obtained by the present invention is fast and effective, and can realize the identification of self-sourced organic carbon components in freshwater rivers, which is of great significance for summarizing and estimating self-sourced organic carbon sinks in terrestrial aquatic systems.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0054] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for estimating the self-sourced soluble organic carbon sink of a freshwater river, characterized in that: The following steps are involved: S1. Collect river water samples from downstream and upstream sections of freshwater rivers, scan and analyze to obtain three-dimensional fluorescence EEM spectra of sample water bodies; use parallel factor analysis to model and obtain the main fluorescent groups in water samples; S2, comparing the excitation and emission spectra of the fluorescent group with the components in the OpenFluor database to obtain the properties and sources of the fluorescent group and obtain the divergent fluorescence intensity of the fluorescent group; S3. According to the properties of the fluorescent group, relevant standard samples are selected to test the divergence intensity of the fluorescent group of organic matter components with different concentrations, and linear fitting model is established to obtain a linear fitting model; S4. Calculate the concentration of endogenous organic matter components in the downstream and upstream sections of freshwater river sections based on the linear fitting model; S5. Calculate the self-sourced dissolved organic carbon sink flux of the river section based on freshwater river flow data; The specific method of step S5 includes the following sub-steps: S5-1, according to the formula: F i =Q i *C i Obtain the self-sourced dissolved organic carbon sink flux F at different river sections i ; where i is up or down; Q i is the flow rate at the river section i, C i is the concentration of self-sourced organic matter at river section i; S5-2, according to the formula: ΔF=F down -F up Obtain the self-source dissolved organic carbon sink flux of the river section ΔF; where F down and F up They are the self-source dissolved organic carbon sink flux in the downstream and upstream sections of the river section.

2. The method for estimating the self-source soluble organic carbon sink of freshwater rivers according to claim 1, characterized in that: In step S3, the linear fitting model is y=ax+b, wherein y is the concentration of the organic component; x is the emission intensity of the fluorescent group; and a and b are linear fitting constants.

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