River nitrogen pollutant source analysis method based on drainage basin nitrogen turnover and isotope

Abstract

The invention discloses a river nitrogen pollutant source analysis method based on drainage basin nitrogen turnover and isotope, and particularly relates to the technical field of water treatment.The river nitrogen pollutant source analysis method comprises the following steps that a drainage basin to be researched is selected, river water and soil samples in the drainage basin are systematically collected, and physical and chemical indexes and isotope indexes # imgabs0 # of the collected samples are tested. Nitrate marked by nitrogen isotope delta 15N / delta 18O and # imgabs1 # are used as key indication marks to perform high-precision identification on nitrogen sources in a river and an environmental system, the contribution proportion of different nitrogen sources to the nitrate concentration in a water body is quantified through a stable isotope analysis model, and the concentration of the nitrate in the water body is calculated. And in combination with data, the rates of denitrification and anaerobic ammonia oxidation in environmental samples, sediments and soil are directly measured through combined application of an isotopic tracer technology and a membrane inlet mass spectrometer technology.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and more specifically, the present invention relates to a method for source analysis of river nitrogen pollutants based on basin nitrogen turnover and isotopes. Background Art

[0002] In river ecosystems, the sources of nitrate are complex and diverse, and may include atmospheric deposition, soil organic nitrogen, sewage, manure, etc. At the same time, nitrate usually undergoes complex physical, chemical, and biological transformation processes, such as nitrification, denitrification, anaerobic ammonia oxidation, and dissimilatory nitrate reduction to ammonia, etc. These transformation processes are often intertwined and difficult to distinguish, thereby increasing the difficulty of nitrate source analysis. In particular, denitrification and anaerobic ammonia oxidation processes can convert nitrate into nitrogen gas, resulting in nitrogen loss, which are key nitrate removal pathways in river ecosystems. However, traditional single research methods are difficult to qualitatively or quantitatively determine the specific sources of nitrate, and it is also difficult to comprehensively analyze these complex nitrogen cycling processes, often resulting in rough results and unclear conclusions.

[0003] Traditional nitrogen source analysis methods mainly rely on chemical composition analysis or single isotope tracing techniques. However, these methods often have limitations in distinguishing the contributions of different nitrogen sources, especially in the case of mixed multiple nitrogen sources, the accuracy and reliability of the analysis results are significantly limited. In addition, existing technologies also have deficiencies in applicability. Most analysis methods are only applicable to specific basins or single nitrogen source types, and have poor analytical effects on multiple nitrogen sources in complex ecosystems, lacking universality and the ability to be widely applied. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a method for source analysis of river nitrogen pollutants based on basin nitrogen turnover and isotopes. By using nitrate labeled with nitrogen isotope δ 15 N / δ 18 O, δ 15 N / δ 18 O-NO3 - as a key indicator, high-precision identification of nitrogen sources in rivers and environmental systems is carried out. Through a stable isotope analysis model, the contribution ratio of different nitrogen sources to the nitrate concentration in water is quantified, and by combining data through the joint application of isotope tracing technology and membrane inlet mass spectrometry technology, the rates of denitrification and anaerobic ammonia oxidation in environmental samples, sediments, and soils are directly measured to solve the problems raised in the above background art.

[0005] To achieve the above object, the present invention provides the following technical solution: A method for source analysis of river nitrogen pollutants based on basin nitrogen turnover and isotopes, comprising the following steps:

[0006] Select the basin to be studied and systematically collect river water and soil samples within the basin;

[0007] Conduct tests on the collected samples for physicochemical indicators and isotope indicator δ 15 N / δ 18 O-NO3 - ;

[0008] Adopt a stable isotope tracing system and method to analyze and identify the main sources of nitrates in the river and their potential transformation processes;

[0009] Construct a simulated slurry mixing system and add 15N isotope labeling to it to determine the rates of denitrification and anammox processes in soil or sediment;

[0010] Compare the results of river source analysis with the rates of the transformation process of NO3 - in soil or sediment in the microenvironment to verify the accuracy of the nitrogen source analysis model.

[0011] In a preferred embodiment, the physicochemical indicators include dissolved oxygen, chlorophyll a, nitrate concentration, and the isotope indicators include δ 15 N and δ 18 O, and their comprehensive characteristic parameter expression formula is:

[0012]

[0013] where Λ represents the comprehensive influence of multiple indicators in the ecological environment or chemical process; ln represents the natural logarithm; DO represents dissolved oxygen; Chl a represents the chlorophyll a concentration; represents the nitrate ion concentration.

[0014] In a preferred embodiment, use a Keeling plot to identify the sources and removal characteristics of nitrate concentration in the river. When the Keeling plot is linear, it indicates that there are two sources of nitrate concentration in the river; when the Keeling plot is curved, it means that there is a multi-source mixing or an obvious nitrate concentration removal process in the river; correct the δ value through the fractionation correction formula to identify the mixing process, and its expression formula is:

[0015] δ corr =δ obs +λ·(ln(C NO3- )-ln(C0))

[0016] where, δ corr represents the corrected isotope value; δ obs represents the observed isotope value; C NO3-represents the current nitrate concentration in water; C0 is the initial nitrate concentration; λ is the fractionation coefficient.

[0017] In a preferred embodiment, the corrected isotope data is quantitatively source-resolved by applying a stable isotope analysis model to quantify the contribution ratio of each nitrate ion NO3 - source to the river nitrate ion NO3 - ; its stable isotope analysis model is based on a Bayesian framework and establishes a logical prior distribution on the Dirichlet distribution. The expression formula of its isotope mixing model is:

[0018]

[0019] where X ij represents the jth isotope value in the ith water sample; P k represents the contribution rate of the kth nitrogen source; the expression formula for the typical isotope characteristics and their variations of each source is:

[0020]

[0021] where S jk represents the jth isotope characteristic value of the kth nitrogen source; when there is an offset caused by denitrification or assimilation, the S jk isotope characteristic value is calibrated by compensating the isotope fractionation effect coefficient. The expression formula for its fractionation coefficient is:

[0022]

[0023] where C jk represents the jth isotope fractionation coefficient of the kth nitrogen source; error compensation is added to ensure the overall accuracy of the model. The error compensation formula is:

[0024]

[0025] where ε ij represents the residual, indicating the influence of unmodeled factors on the observed value X ij .

[0026] In a preferred embodiment, the specific operation of the slurry mixing system includes:

[0027] Prepare 7 12 mL headspace bottles, add 2 g of fresh soil and mix it with helium-treated deionized water at a ratio of 1:5;

[0028] Pre-incubate in a thermostatic shaker at a rotation speed of 200 rpm and the sample point temperature for 72 hours;

[0029] After the pre-culture was completed, 15N isotope-labeled nitrate was added to six of the headspace bottles to a concentration of 100 μmol N / L, and the reaction was terminated using 7 mol / L saturated zinc chloride.

[0030] The membrane inlet mass spectrometer was used to measure 29N2 and 30N2 in the samples, and the total production rate was jointly contributed by denitrification and nitrification. The formula is:

[0031] P 29 = D 29 + A 29

[0032] Among them, P 29 represents the production rate of 29N2 gas in the sample; D 29 represents the rate of 29N2 generated during denitrification; A 29 represents the rate of 29N2 generated during anammox. The formula for the production rate of 29N2 from 15N and 14N gases is:

[0033]

[0034] Among them, P 30 represents the measured production rate of 30N2 gas in the sample; F N represents the proportion of 15N in nitrate; represents the proportion of 14N in nitrate. The formula for the contribution of denitrification to the total N2 production rate is expressed as:

[0035] D t = D 29 + 2 × P 30

[0036] Among them, D 29 represents the rate of 29N2 generated during denitrification; 2 × P 30 represents twice the rate of 30N2 gas generated by denitrification. The formula for the contribution of nitrification to the 29N2 production rate is expressed as:

[0037] A 29 = P 29 - D 29

[0038] Among them, P 29 represents the production rate of 29N2 gas in the sample; P 30 represents the measured production rate of 30N2 gas in the sample; D 29 represents the rate of 29N2 generated during denitrification. Among them, the formula for the contribution of denitrification and nitrification to N2 production is expressed as:

[0039] D t = P30 ·(2·F N ·(1 - F N ) -1 )

[0040] A t =P 29 - D t

[0041] Wherein, P 29 represents the production rate of 29N2 gas in the sample; P 30 represents the measured production rate of 30N2 gas in the sample; A t is the contribution of nitrification to the total N2 production rate; D t is the contribution of denitrification to the total N2 production rate; F N represents the proportion of 15N in the total NO3 - .

[0042] In a preferred embodiment, the nitrogen source contribution rate is quantified by combining the isotope mixing model to ensure the accuracy of the model. The calculation formula for the nitrogen source contribution rate is:

[0043]

[0044] Wherein, P k represents the contribution rate of the kth nitrogen source; X ij represents the jth isotope value in the ith water sample; C jk represents the jth isotope fractionation coefficient of the kth nitrogen source; S jk represents the jth isotope characteristic value of the kth nitrogen source; is the likelihood function; N represents the number of samples; K represents the types of nitrogen sources; J represents the types of isotopes.

[0045] In a preferred embodiment, the coincidence degree between the model prediction value and the observed value is verified by the residual formula. The residual formula is:

[0046]

[0047] Wherein, E represents the error check value; represents the observed value of the ith sample; represents the predicted value of the ith sample; N represents the number of samples.

[0048] Technical effects and advantages of the present invention:

[0049] 1. Using nitrate labeled with nitrogen isotope δ 15 N / δ 18 O, δ 15 N / δ 18 O - NO3 -As a key indicator, it accurately identifies nitrogen sources in rivers and environmental systems. Through a stable isotope analysis model, it quantifies the contribution ratio of different nitrogen sources to the nitrate concentration in water bodies, and combines data to clearly show the dynamic process of the nitrogen cycle in complex environments. In addition, through the combined application of isotope tracing technology and membrane inlet mass spectrometry technology, it directly measures the rates of denitrification and anammox in environmental samples, sediments, and soils;

[0050] 2. By utilizing the unique characteristics of δ 15 N / δ 18 O isotopes, it differentiates different nitrogen sources such as agricultural runoff, domestic sewage, and precipitation to provide clear sources. Secondly, by introducing a stable isotope analysis model and combining isotope data with probability distributions, it ensures more accurate analysis of nitrogen source ratios. Finally, the membrane inlet mass spectrometer directly measures the rates of denitrification and anammox, breaking through the limitations of traditional methods for indirectly estimating reaction rates, thereby further revealing the key links in the nitrogen cycle process. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] Referring to the attached Figure 1 description, a method for analyzing the sources of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to an embodiment of the present invention includes the following steps:

[0054] Select the watershed to be studied and systematically collect river water and soil samples within the watershed;

[0055] Test the physicochemical indexes and isotope index δ 15 N / δ 18 O-NO3 - for the collected samples;

[0056] Adopt a stable isotope tracing system and method to analyze and identify the main sources of nitrates in the river and their potential transformation processes;

[0057] Construct a simulated slurry mixing system and add 15N isotope labeling to it to measure the rates of denitrification and anammox processes in soils or sediments;

[0058] Compare the river source analysis results with the transformation process rate of NO3 in soil or sediment in the microenvironment to verify the accuracy of the nitrogen source analysis model; -

[0059] The physicochemical indicators include dissolved oxygen, chlorophyll a, and nitrate concentration. Among them, the isotope indicators include δ 15 N and δ 18 O, and the expression formula for its comprehensive characteristic parameters is:

[0060]

[0061] Among them, Λ represents the comprehensive influence of multiple indicators in the ecological environment or chemical process; ln represents the natural logarithm, that is, calculating the logarithm of this value; DO represents dissolved oxygen, the concentration of oxygen dissolved in water, which is an important indicator for measuring water body health and ecosystem function; Chl a represents the chlorophyll a concentration. By measuring the concentration of chlorophyll a in water, the photosynthetic activity of plants can be judged, and the number of phytoplankton in the water body can also be indirectly reflected; represents the nitrate ion concentration. Nitrate is a common nutrient salt in water bodies. High concentrations of nitrate may indicate that the water body is polluted by agricultural fertilization or sewage; represents a positive decimal constant; when calculating the second term in the formula, the nitrate ion concentration may be zero, resulting in a division by zero situation in the formula. To avoid this situation, a constant is added to the nitrate ion concentration to make the denominator always greater than zero, thus ensuring that the calculation can proceed; by combining three main ecological and water quality indicators, DO dissolved oxygen, Chl a chlorophyll a and nitrate concentration and a constant to avoid division by zero errors, by calculating the natural logarithm of the product of DO and Chl a its expression formula is:

[0062] ln(DO·Chl a )

[0063] Among them, the calculated value of this term reflects the photosynthetic activity of phytoplankton in the water body and the concentration of dissolved oxygen; the reason for taking the logarithm after the product is to compress the numerical range to make it more suitable for analysis, and then calculate the nitrate concentration in the water body its expression formula is:

[0064]

[0065] Among them, the calculated value of this term is the nitrate concentration ​The reciprocal of the square root after adding a constant, through the square root operation, the formula can appropriately scale the nitrate concentration; the purpose of adding is to prevent from causing a zero denominator when it is zero;

[0066] By selecting the basins within the study area and systematically collecting river water bodies and surrounding soil samples within the basins, the physicochemical indices of the samples, dissolved oxygen concentration, chlorophyll a concentration, nitrate concentration and isotope characteristics, nitrogen isotope ratio δ 15 N and oxygen isotope ratio δ 18 O are tested. The dissolved oxygen concentration reflects the health status of the water body and the function of the ecosystem; the chlorophyll a concentration indirectly assesses the eutrophication degree of the water body through the photosynthetic activity of phytoplankton; the nitrate concentration indicates the possible pollution level of the water body by agricultural runoff or domestic sewage. Combining the data of these indices can preliminarily evaluate the ecological characteristics of nitrogen pollution and the water quality status of the basin;

[0067] Using the stable isotope tracing technique, analyze the main sources of nitrate in the river and its potential transformation process. Through the ratios of stable isotopes δ 15 N and δ 18 O, various potential nitrogen sources such as agricultural runoff, domestic sewage, precipitation and soil mineralization can be accurately distinguished. In addition, these isotope characteristics can also capture the transformation paths of nitrate in the environment, such as denitrification, assimilation and anaerobic ammonium oxidation. The tracer analysis provides quantitative data support for source analysis, enabling it to effectively locate the sources and destinations of nitrogen pollution;

[0068] Using the Keeling plot to identify the sources and removal characteristics of nitrate concentration in the river. First, when the Keeling plot is linear, it indicates that there are two main sources of nitrate concentration in the river. The nitrate in the river mainly comes from farmland runoff and domestic sewage; further, when the Keeling plot is curved, it means that there is a multi-source mixing or an obvious nitrate concentration removal process in the river, and when the linear slope of is about 1, it indicates that there is a significant denitrification process; correct the δ value through the fractionation correction formula to identify the mixing process, and its expression formula is:

[0069] δ corr =δ obs +λ·(ln(C NO3- ))-ln(C0))

[0070] where, δ corr represents the corrected isotope value, which is finally used to analyze the source of nitrate; δ obs represents the observed isotope value, that is, the data measured in the experiment; C NO3-represents the current nitrate concentration in water; C0 is the initial nitrate concentration; λ is the fractionation coefficient, indicating the degree of isotope change of nitrate under biological action. By analyzing and the linear relationship between them, if the slope is close to 1, it further indicates that significant denitrification processes have occurred in the watershed. These denitrification processes may include assimilation, denitrification, or anammox. On this basis, by considering environmental parameters such as dissolved oxygen and chlorophyll a, the relative importance of the nitrate ion removal pathways can be further evaluated; next, according to the sources of each nitrate ion in the river, the specific δ 15 N / eigenvalue ranges of precipitation and sewage, the potential end members affecting the river isotope values are determined. For the situation where obvious nitrate ion removal processes occur, the isotope fractionation phenomenon needs to be considered, and then the isotope values are corrected to the initial state according to the regression line of the fractionation trend;

[0071] Using nitrogen isotope δ 15 N / δ 18 O-labeled nitrate, as a key indicator, the nitrogen sources in the river and environmental systems are accurately identified. Through the stable isotope analysis model, the contribution ratios of different nitrogen sources to the nitrate concentration in the water body are quantified, and combined with the data, the dynamic process of the nitrogen cycle in the complex environment is clearly shown. In addition, through the combined application of isotope tracer technology and membrane inlet mass spectrometry technology, the rates of denitrification and anammox in environmental samples, sediments, and soils are directly measured;

[0072] The corrected isotope data is quantitatively source-resolved by applying the stable isotope analysis model to quantify the contribution ratios of the sources of each nitrate ion to the river nitrate ion ; its stable isotope analysis model is based on the Bayesian framework and establishes a logical prior distribution on the Dirichlet distribution to ensure that the sum of the contribution ratios of all sources is 100%. The expression formula of its isotope mixing model is:

[0073]

[0074] Among them, X ij represents the jth isotope value in the ith water sample, where i = 1, 2,..., N. Further, j = 1, 2,..., j; P k represents the contribution rate of the kth nitrogen source and satisfies The typical isotope characteristics and their changes of each source are expressed by the formula:

[0075]

[0076] Among them, S jk represents the j-th isotope eigenvalue of the k-th nitrogen source, following a normal distribution with a mean of μ jk and a variance of , describing the typical isotope characteristics and their variation ranges of each source; when there is an offset caused by denitrification or assimilation, the S jk isotope eigenvalue is calibrated by compensating the isotope fractionation effect coefficient, and its fractionation coefficient expression formula is:

[0077]

[0078] Among them, C jk represents the j-th isotope fractionation coefficient of the k-th nitrogen source, following a normal distribution with a mean of λ jk and a variance of ; C jk is used to correct the value of S jk , compensating the isotope fractionation effect; adding error compensation to ensure the overall accuracy of the model, and its error compensation formula is:

[0079]

[0080] Among them, ε ij represents the residual, indicating the influence of unmodeled factors on the observed value X ij , and is determined based on its mean value μ k and variance ω k ; it is determined by its mean value λ k and variance τ k ; ε ij represents the residual term, indicating the unquantified variance, usually set to 0; through further analysis of the above parameters, the mixing model can quantitatively analyze the contributions of different sources of nitrate ions in rivers to the nitrate ions in rivers , so as to analyze the sources of nitrogen in water bodies. S jk defines the isotope characteristic range of each nitrogen source as the input data of the model; P k is the contribution rate of each nitrogen source, controlling the weighted effect of each S jk ; C jk is used to correct S jk to make the isotope eigenvalue more in line with the actual chemical process, while ε ij ensures that the model has a certain flexibility to accommodate uncontrollable deviations in the data; its isotope mixing model solves the source characteristic differences in the isotope mixing model through the distribution assumptions of S jk , C jk and ε ij ​jk Captured the uniqueness of each nitrogen source, C jk Corrected the eigenvalue with the fractionation effect to make the result closer to reality, statistical accuracy, ε ij Compensated for the deviation of unmodeled factors. Based on the corrected isotope data, the stable isotope mixing model was used to quantitatively analyze the contribution rate of nitrogen sources. The model was based on the Bayesian framework and used the Dirichlet distribution as the logical prior distribution to ensure that the sum of the contribution rates of all nitrogen sources was 100%.

[0081] The specific operations of the slurry mixing system include:

[0082] Prepare 7 headspace vials of 12 mL, add 2 g of fresh soil and mix it with deionized water treated with helium in a ratio of 1:5;

[0083] Pre-culture in a constant temperature shaker at a rotation speed of 200 rpm and the sample point temperature for 72 hours;

[0084] After the pre-culture, add 15N isotope-labeled nitrate to 6 of the headspace vials to make its concentration 100 μmol N / L, and use 7 mol / L saturated zinc chloride to terminate the reaction;

[0085] Use a membrane inlet mass spectrometer to measure 29N2 and 30N2 in the sample. The total production rate is jointly contributed by denitrification and nitrification. The formula is:

[0086] P 29 = D 29 + A 29

[0087] Among them, P 29 represents the production rate of 29N2 gas in the sample, and the unit is micromoles of nitrogen per kilogram per hour; D 29 represents the rate of 29N2 generated during the denitrification process, and the unit is micromoles of nitrogen per kilogram per hour; A 29 represents the rate of 29N2 generated during the anaerobic ammonium oxidation process; by measuring the production rate P of 29N2 gas measured in the sample 29 , it can be decomposed into the contribution D of denitrification 29 and the contribution A of anaerobic ammonium oxidation 29 ; using the ratio of different isotopes 15N and 14N in the sample, the rate D of 29N2 gas generated by denitrification is deduced 29 , and the formula for the production rate of 29N2 generated by 15N and 14N gases is:

[0088]

[0089] Among them, P 30Represents the rate of 30N2 gas production measured in the sample; F N Represents the proportion of 15N in nitrate; Represents the proportion of 14N in nitrate; By combining the production rates of 29N2 and 30N2, the total denitrification rate is calculated, and the formula for the contribution of denitrification to the total N2 production rate is expressed as:

[0090] D t = D 29 + 2×P 30

[0091] Where, D 29 Represents the rate of 29N2 produced during the denitrification process; 2×P 30 Represents twice the rate of 30N2 gas produced by denitrification; By combining the production rates of 29N2 and 30N2, the total denitrification rate D t is calculated to quantify the overall contribution of denitrification; The formula for the contribution of nitrification to the 29N2 production rate is expressed as:

[0092] A 29 = P 29 - D 29

[0093] Where, P 29 Represents the rate of 29N2 gas production in the sample; P 30 Represents the rate of 30N2 gas production measured in the sample; D 29 Represents the rate of 29N2 produced during the denitrification process; Through the calculation of D 29 and A 29 , the rate contributions of denitrification and anammox to nitrogen production are quantified respectively, and the source of nitrogen pollution and the efficiency of nitrogen removal in the river are confirmed. Among them, the formulas for the contributions of denitrification and nitrification to N2 production are expressed as:

[0094] D t = P 30 ·(2·F N ·(1 - F N )) -1 ))

[0095] A t = P 29 - D t

[0096] Where, P 29 Represents the rate of 29N2 gas production in the sample; P 30 Represents the rate of 30N2 gas production measured in the sample; A t is the contribution of nitrification to the total N2 production rate; D tContribution of denitrification to the total N2 production rate, including the production rates of 29N2 and 30N2; F N represents the proportion of 15N in the total and the enrichment degree of isotope labeling; from the production rates of 29N2 and 30N2, and the proportion F of 15N N the rates of denitrification and anammox can be separated and calculated; by separating and quantifying the contributions of denitrification and anammox to nitrogen production, and experimentally measuring P 29 P 30 F N parameters, the nitrogen production rates of each process are calculated, and these rates are further used to analyze the sources and transformation processes of nitrogen pollutants in rivers. During denitrification and anammox processes, and are converted to nitrogen gas N2, and different combinations of N2, such as 29N2 and 30N2, will be generated according to the isotope enrichment degree. If the production rate of 30N2 is high, it indicates that denitrification dominates because this process is more dependent on the combination of two 15NO3 - molecules;

[0097] To further verify the accuracy of the nitrogen pollution source analysis model, a simulated slurry mixing system was constructed. The specific operation was as follows: Add 2 g of fresh soil to 7 12-mL headspace bottles, and mix with deionized water at a ratio of 1:5. Pre-incubate in a constant temperature shaker at a rotation speed of 200 rpm for 72 hours. Subsequently, add 15N isotope-labeled nitrate solution with a concentration of 100 μmol N / L to 6 headspace bottles, and use 7 mol / L saturated zinc chloride to terminate the reaction. Measure the production rates of 29N2 and 30N2 gases in the system by a membrane inlet mass spectrometer. By simulating the rates of denitrification and anammox in soil or sediment, reliable microscopic verification data are provided for the watershed analysis model;

[0098] By combining the isotope mixing model to quantify the nitrogen source contribution rate and ensure the accuracy rate of the model, the calculation formula for its nitrogen source contribution rate is:

[0099]

[0100] where P k represents the contribution rate of the kth nitrogen source; represents the summation over all samples; represents the product of multiple isotope values for each sample; (X ij ∣C jk ·S jk ) represents the summation over all k nitrogen sources; X ij represents the jth isotope value in the ith water sample; Cjk represents the j-th isotope fractionation coefficient of the k-th nitrogen source; S jk represents the j-th isotope eigenvalue of the k-th nitrogen source; is the likelihood function, representing the matching degree between the observed data and the hypothesized model; N represents the number of samples; K represents the types of nitrogen sources; J represents the types of isotopes; the model for calculating the contribution rate of nitrogen sources is used for quantitative calculation of different nitrogen sources, precipitation, sewage, and agricultural runoff to nitrate ions in the river of the contribution ratio, by inputting the isotope ratio X of the observed sample ij and the eigenvalue S of each nitrogen source jk , combined with the fractionation coefficient C jk , estimate the contribution rate of each nitrogen source to ensure the accuracy of the model,

[0101] Verify the consistency between the predicted value and the observed value of the model through the residual formula, and its residual formula is:

[0102]

[0103] where E represents the error check value; represents the observed value of the i-th sample; represents the predicted value of the i-th sample; N represents the number of samples;

[0104] By combining multiple technologies, the problems of insufficient accuracy and large variation in conversion coefficients in the existing technology for nitrogen source analysis are solved. Traditional methods often have difficulty effectively distinguishing the main pollution sources in a complex mixed nitrogen source environment and are susceptible to parameter fluctuations in quantitative analysis, resulting in deviations in the analysis results. Through the labeling and dynamic tracking of isotope indicators, combined with the quantitative analysis of multi-source contribution rates, the accuracy and reliability of nitrogen source analysis can be significantly improved. Especially under the complex conditions of mixed nitrogen sources, this solution can effectively identify the main pollution contributors and provide clear source analysis results.

[0105] Compared with the traditional method, first, utilize the unique characteristics of δ 15 N / δ 18 O isotopes to distinguish different nitrogen sources such as agricultural runoff, domestic sewage, and precipitation, providing clear sources; secondly, by introducing a stable isotope analysis model and combining isotope data with probability distributions, ensure more accurate analysis of nitrogen source proportions; finally, the membrane inlet mass spectrometer directly measures the rates of denitrification and anaerobic ammonium oxidation, breaking through the limitations of indirect estimation of reaction rates by traditional methods, thereby further revealing the key links in the nitrogen cycle process.

[0106] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for source analysis of river nitrogen pollutants based on watershed nitrogen turnover and isotopes, characterized in that, Including the following steps: Select the basin to be studied and systematically collect river water and soil samples within the basin; Perform tests on the collected samples for physicochemical indicators and isotope indicators ; Adopt a stable isotope tracer system and method to analyze and identify the main sources of nitrate in the river and its potential transformation processes; Construct a simulated slurry mixing system and add 15N isotope labeling to it to measure the rates of denitrification and anammox processes in soil or sediment; Compare the river source analysis results with the transformation process rates in soil or sediment in the microenvironment to verify the accuracy of the nitrogen source analysis model.

2. The method for analyzing the sources of river nitrogen pollutants based on basin nitrogen turnover and isotopes according to claim 1, wherein: Physicochemical indicators include dissolved oxygen, chlorophyll a, nitrate concentration, among which isotope indicators include δ 15 N and δ 18 O, and the expression formula for its comprehensive characteristic parameters is: Among them, Λ represents the comprehensive impact of multiple indicators in the ecological environment or chemical process; ln represents the natural logarithm; DO represents dissolved oxygen; Chl a represents the concentration of chlorophyll a; NO3 - represents the concentration of nitrate ions.

3. The method for analyzing the sources of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 2, wherein: Using a Keeling plot To identify the sources and removal characteristics of nitrate concentration in a river, when the Keeling plot is linear, it indicates that there are two sources of nitrate concentration in the river; when the Keeling plot is curved, it means that multi-source mixing or an obvious nitrate concentration removal process has occurred in the river; the δ value is corrected by the fractionation correction formula to identify the mixing process, and its expression formula is: δ corr = δ obs + λ·(ln(C NO3- ) - ln(C0)) Among them, δ corr represents the corrected isotope value; δ obs represents the observed isotope value; C NO3- represents the current concentration of nitrate in water; C0 is the initial nitrate concentration; λ is the fractionation coefficient.

4. A method for source analysis of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 3, characterized in that: The calibrated isotope data are used for quantitative source analysis by applying a stable isotope analysis model to quantify the contribution ratio of each nitrate ion source to the nitrate ions in the river ; Its stable isotope analysis model is based on a Bayesian framework and establishes a logical prior distribution on the Dirichlet distribution. The expression formula of its isotope mixing model is: Among them, X ij represents the value of the j-th isotope in the i-th water sample; P k represents the contribution rate of the k-th nitrogen source; the typical isotope characteristics and their variation expression formulas of each source are as follows: Among them, S jk represents the j-th isotope eigenvalue of the k-th nitrogen source; when there is an offset caused by denitrification or assimilation, the isotope eigenvalue of S jk is calibrated by compensating the isotope fractionation effect coefficient, and its fractionation coefficient expression formula is: Among them, C jk represents the j-th isotope fractionation coefficient of the k-th nitrogen source; adding error compensation ensures the overall accuracy of the model, and its error compensation formula is: Among them, ε ij represents the residual, representing the influence of unmodeled factors on the observed value X ij .

5. A method for analyzing the sources of river nitrogen pollutants based on basin nitrogen turnover and isotopes according to claim 4, characterized in that: The specific operation of the slurry mixing system includes: Prepare 7 12-mL headspace bottles, add 2 g of fresh soil and mix it with helium-treated deionized water at a ratio of 1:5; Pre-culture in a constant temperature shaker at a rotation speed of 200 rpm and the sample point temperature for 72 hours; After the pre-culture is completed, add 15N isotope-labeled nitrate to 6 of the headspace bottles to make its concentration 100 μmol N / L, and use 7 mol / L saturated zinc chloride to terminate the reaction; Use a membrane inlet mass spectrometer to measure 29N2 and 30N2 in the sample. The total production rate is jointly contributed by denitrification and nitrification. The formula is: P 29 = D 29 + A 29 Among them, P 29 represents the production rate of 29N2 gas in the sample; D 29 represents the rate of 29N2 produced during the denitrification process; A 29 represents the rate of 29N2 produced during the anammox process; the production rate formula of 29N2 from its 15N and 14N gases is as follows: Among them, P 30 represents the generation rate of 30N2 gas measured in the sample; F N represents the proportion of 15N in nitrate; represents the proportion of 14N in nitrate; The contribution formula of its denitrification to the total N2 generation rate is expressed as: D t = D 29 + 2 × P 30 Among them, D 29 represents the rate of 29N2 generated during the denitrification process; 2×P 30 represents twice the rate of 30N2 gas generated by denitrification; the expression formula for the contribution of nitrification to the generation rate of 29N2 is: A 29 = P 29 - D 29 Among them, P 29 represents the production rate of 29N2 gas in the sample; P 30 represents the measured production rate of 30N2 gas in the sample; D 29 represents the rate of 29N2 produced during the denitrification process; among them, the contribution formula of denitrification and nitrification to N2 production is expressed as: D t = P 30 ·(2·F N ·(1 - F N ) -1 ) A t = P 29 - D t Among them, P 29 represents the generation rate of 29N2 gas in the sample; P 30 represents the measured generation rate of 30N2 gas in the sample; A t is the contribution of nitrification to the total N2 generation rate; D t is the contribution of denitrification to the total N2 generation rate; F N represents the proportion of 15N in the total .

6. The method for analyzing the sources of river nitrogen pollutants based on basin nitrogen turnover and isotopes according to claim 5, characterized in that: By combining the isotope mixing model to quantify the nitrogen source contribution rate and ensure the accuracy of the model. The formula for calculating the nitrogen source contribution rate is: Among them, P k represents the contribution rate of the k-th nitrogen source; X ij represents the j-th isotope value in the i-th water sample; C jk represents the j-th isotope fractionation coefficient of the k-th nitrogen source; S jk represents the j-th isotope characteristic value of the k-th nitrogen source; is the likelihood function; N represents the number of samples; K represents the types of nitrogen sources; J represents the types of isotopes.

7. A method for source analysis of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 6, characterized in that: Verify the coincidence degree between the model prediction value and the observed value through the residual formula. The residual formula is: Among them, E represents the error check value; represents the observed value of the i-th sample; represents the predicted value of the i-th sample; N represents the number of samples.

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