A river nitrogen pollutant source analysis method based on catchment nitrogen turnover and isotope

Abstract

This invention discloses a method for source apportionment of nitrogen pollutants in rivers based on watershed nitrogen turnover and isotopes, specifically relating to the field of water treatment technology. The method includes the following steps: selecting the watershed to be studied, systematically collecting river water and soil samples from the watershed, and analyzing the collected samples for physicochemical and isotopic indices. The test. This invention utilizes the nitrogen isotope δ. 15 N / δ 18 O-labeled nitrates, As a key indicator, it enables high-precision identification of nitrogen sources in rivers and environmental systems. Through stable isotope analysis models, it quantifies the contribution ratio of different nitrogen sources to nitrate concentration in water bodies. Combined with data, it directly measures the rates of denitrification and anaerobic ammonia oxidation in environmental samples, sediments, and soils through the combined application of isotope tracing technology and membrane inlet mass spectrometry.

Description

A method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically, to a method for source apportionment of nitrogen pollutants in rivers based on watershed nitrogen turnover and isotopes. Background Technology

[0002] In river ecosystems, nitrates have diverse and complex sources, including atmospheric deposition, soil organic nitrogen, sewage, and manure. Furthermore, nitrates typically undergo complex physical, chemical, and biological transformation processes, such as nitrification, denitrification, anaerobic ammonium oxidation, and the dissimilatory reduction of nitrates to ammonia. These processes are often intertwined and difficult to distinguish, increasing the difficulty of identifying nitrate sources. Denitrification and anaerobic ammonium oxidation, in particular, convert nitrates into nitrogen gas, leading to nitrogen loss and representing key nitrate removal pathways in river ecosystems. However, traditional single-method research is insufficient to qualitatively or quantitatively identify the specific sources of nitrates, and it also struggles to comprehensively analyze these complex nitrogen cycle processes, often resulting in crude results and unclear conclusions.

[0003] Traditional nitrogen source apportionment 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 multiple nitrogen sources mixed together, where the accuracy and reliability of the apportionment results are significantly limited. In addition, existing technologies also have shortcomings in terms of applicability. Most apportionment methods are only applicable to specific watersheds or single nitrogen source types, and their apportionment effect on multiple nitrogen sources in complex ecosystems is poor, lacking universality and the ability to be widely applied. Summary of the Invention

[0004] To overcome the aforementioned shortcomings of existing technologies, embodiments of the present invention provide a river nitrogen pollutant source apportionment method based on watershed nitrogen turnover and isotopes, by employing nitrogen isotope δ¹⁸O. 15 N / δ 18 O-labeled nitrates, δ 15 N / δ 18 O-NO3 - As a key indicator, this method enables high-precision identification of nitrogen sources in rivers and environmental systems. Through stable isotope analysis models, it quantifies the contribution ratio of different nitrogen sources to nitrate concentration in water bodies. Furthermore, by combining data with isotope tracing technology and membrane inlet mass spectrometry, it directly measures the rates of denitrification and anaerobic ammonia oxidation in environmental samples, sediments, and soils, thereby addressing the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes, comprising the following steps:

[0006] The watershed to be studied was selected, and river water and soil samples were systematically collected within the watershed.

[0007] The collected samples were analyzed for physicochemical and isotopic parameters, including δ¹⁸O values. 15 N / δ 18 O-NO3 - The test;

[0008] Stable isotope tracing systems and methods were used to analyze and identify the main sources of nitrates in rivers and their potential transformation processes;

[0009] A simulated mud mixing system was constructed and labeled with 15N isotope to determine the rates of denitrification and anaerobic ammonium oxidation in soil or sediment.

[0010] The results of river source apportionment were compared with NO3 in soil or sediment in the microenvironment. - The conversion process rate was compared to verify the accuracy of the nitrogen source analysis model.

[0011] In a preferred embodiment, the physicochemical indicators include dissolved oxygen, chlorophyll a, and nitrate concentration, wherein the isotopic indicators include δ¹⁸O⁻. 15 N and δ 18 O, whose comprehensive characteristic parameter expression formula is:

[0012]

[0013] Where Λ represents the combined impact of multiple indicators in the ecological environment or chemical process; ln represents the natural logarithm; DO represents dissolved oxygen; Chl a Indicates chlorophyll a concentration; This indicates the concentration of nitrate ions.

[0014] In a preferred embodiment, using a Kirchhoff plot To identify the sources and removal characteristics of nitrate concentration in rivers, a linear Killerlin plot indicates two sources of nitrate concentration in the river; a curved Killerlin plot indicates multi-source mixing or a significant nitrate removal process. The mixing process can be identified by correcting the δ value using a fractionation correction formula, which is expressed as follows:

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

[0016] Where, δ corr Indicates the corrected isotope value; δ obs Indicates the observed isotope value; C NO3- The current concentration of nitrate in the water is represented by C0; the initial nitrate concentration is represented by C0; and λ is the fractionation coefficient.

[0017] In a preferred embodiment, the corrected isotope data are quantitatively source-analyzed using a stable isotope analysis model to quantify each nitrate ion (NO3). - Sources of nitrate ions (NO3) from rivers - The contribution ratio; its stable isotope analysis model is based on a Bayesian framework and establishes a logical prior distribution on the Dirichlet distribution. The formula for its isotope mixing model is:

[0018]

[0019] Among them, X ij P represents the value of the j-th isotope in the i-th water sample; k Let represent the contribution rate of the k-th nitrogen source; the typical isotopic characteristics and their variations from each source are expressed by the following formulas:

[0020]

[0021] Among them, S jk This represents the characteristic value of the j-th isotope of the k-th nitrogen source; when the shift is caused by denitrification or assimilation, the isotope fractionation effect coefficient is compensated for by adjusting S. jk The fractionation coefficient is expressed by the following formula after calibration of isotopic characteristic values:

[0022]

[0023] Among them, C jk Let represent the fractionation coefficient of the j-th isotope from the k-th nitrogen source; error compensation is added to ensure the overall accuracy of the model, and the error compensation formula is:

[0024]

[0025] Where, ε ij Represents the residual, indicating the effect of unmodeled factors on the observed value X. ij The impact.

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

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

[0028] Pre-culture for 72 hours in a constant temperature shaker at 200 rpm and sample temperature;

[0029] After the pre-culture was completed, 15N isotope-labeled nitrate was added to 6 of the headspace vials to make its concentration 100 μmol N / L, and the reaction was terminated with 7 mol / L saturated zinc chloride.

[0030] The total formation rate of 29N2 and 30N2 in the sample was determined using a membrane inlet mass spectrometer. The formula for the combined contribution of denitrification and nitrification is as follows:

[0031] P 29 =D 29 +A 29

[0032] Among them, P 29 Indicates the generation rate of 29N2 gas in the sample; D 29 Indicates the rate at which 29N2 is generated during denitrification; A 29 The rate at which 29N2 is generated during anaerobic ammonia oxidation is expressed; the formula for the rate at which 15N and 14N gases generate 29N2 is:

[0033]

[0034] Among them, P 30 This indicates the rate of 30N2 gas generation measured in the sample; F N This indicates the proportion of 15N in nitrates; The proportion of 14N in nitrates is represented by the formula for the contribution of denitrification to the total N2 formation rate:

[0035] D t =D 29 +2×P 30

[0036] Among them, D 29 This represents the rate at which 29N2 is generated during denitrification; 2×P 30 This represents twice the rate of 30N2 gas produced by denitrification; the formula expressing the contribution of nitrification to the 29N2 formation rate is:

[0037] A 29 =P 29 -D 29

[0038] Among them, P 29 P represents the generation rate of 29N2 gas in the sample. 30 D represents the measured rate of N2 gas generation in the sample.29 This represents the rate at which 29N2 is generated during denitrification; the contribution of denitrification and nitrification to N2 formation is expressed by the following formula:

[0039] D t =P 30 ·(2·F N ·(1-F N ) -1 )

[0040] A t =P 29 -D t

[0041] Among them, P 29 P represents the generation rate of 29N2 gas in the sample. 30 Indicates the measured rate of N2 gas generation in the sample; A t The contribution of nitrification to the overall N2 formation rate; D t The contribution of denitrification to the total N2 formation rate; F N This indicates that 15N is present in the total NO3. - The proportion in.

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

[0043]

[0044] Among them, P k X represents the contribution rate of the k-th nitrogen source; ij C represents the value of the j-th isotope in the i-th water sample; jk S represents the fractionation coefficient of the j-th isotope from the k-th nitrogen source; jk This represents the characteristic value of the j-th isotope of the k-th nitrogen source; is the likelihood function; N represents the number of samples; K represents the type of nitrogen source; J represents the type of isotope.

[0045] In a preferred embodiment, the good agreement between the model predictions and the observed values ​​is verified using a residual formula, which is:

[0046]

[0047] Where E represents the error check value; This represents the observed value of the i-th sample; represents the predicted value of the i-th sample; N represents the number of samples.

[0048] The technical effects and advantages of this invention are as follows:

[0049] 1. Using nitrogen isotope δ 15 N / δ 18 O-labeled nitrates, δ 15 N / δ 18 O-NO3 - As a key indicator, it can accurately identify nitrogen sources in rivers and environmental systems. Through stable isotope analysis models, it can quantify the contribution ratio of different nitrogen sources to nitrate concentration in water bodies. Combined with data, it can clearly show the dynamic process of nitrogen cycle in complex environments. In addition, through the combined application of isotope tracing technology and membrane inlet mass spectrometry technology, it can directly measure the rate of denitrification and anaerobic ammonium oxidation in environmental samples, sediments and soil.

[0050] 2. By utilizing δ 15 N / δ 18 The unique properties of the O isotope distinguish different nitrogen sources such as agricultural runoff, domestic sewage, and precipitation, providing a clear source. Secondly, by introducing a stable isotope analysis model, the isotope data is combined with probability distribution to ensure more accurate analysis of nitrogen source proportions. Finally, the membrane inlet mass spectrometer directly measures the rates of denitrification and anaerobic ammonia oxidation, breaking through the limitations of traditional methods that indirectly estimate reaction rates, thereby further revealing the key links in the nitrogen cycle process. Attached Figure Description

[0051] Figure 1 is a schematic diagram of the process of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Referring to Figure 1 in the specification, an embodiment of the present invention provides a method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes, comprising the following steps:

[0054] The watershed to be studied was selected, and river water and soil samples were systematically collected within the watershed.

[0055] The collected samples were analyzed for physicochemical and isotopic parameters, including δ¹⁸O values. 15 N / δ 18 O-NO3 - The test;

[0056] Stable isotope tracing systems and methods were used to analyze and identify the main sources of nitrates in rivers and their potential transformation processes;

[0057] A simulated mud mixing system was constructed and labeled with 15N isotope to determine the rates of denitrification and anaerobic ammonium oxidation in soil or sediment.

[0058] The results of river source apportionment were compared with NO3 in soil or sediment in the microenvironment. - The conversion process rate was compared to verify the accuracy of the nitrogen source analysis model.

[0059] Physicochemical indicators include dissolved oxygen, chlorophyll a, and nitrate concentration, among which isotopic indicators include δ¹⁸O⁻. 15 N and δ 18 O, whose comprehensive characteristic parameter expression formula is:

[0060]

[0061] Where Λ represents the combined impact of multiple indicators in the ecological environment or chemical process; ln represents the natural logarithm, which is the logarithm of the calculated value; DO represents dissolved oxygen, the concentration of dissolved oxygen in water, which is an important indicator for measuring water health and ecosystem function; Chl a It represents the concentration of chlorophyll a. By measuring the concentration of chlorophyll a in water, we can determine the photosynthetic activity of plants and indirectly reflect the amount of phytoplankton in the water. This indicates the concentration of nitrate ions. Nitrate is a common nutrient in water bodies, and a high concentration may indicate pollution from agricultural fertilization or wastewater. It also represents a positive decimal constant. In the second term of the calculation formula... The nitrate ion concentration may be zero, leading to division by zero in the formula. To avoid this, a constant is added. Regarding nitrate ion concentration, the denominator is always kept greater than zero to ensure the calculation can continue; this is achieved by combining three main ecological and water quality indicators: dissolved oxygen (DO), dissolved oxygen (Chl), and nitrate concentration. a Chlorophyll a and nitrate concentration And a constant to avoid division by zero error, by calculating DO and Chl a The natural logarithm of the product of is expressed as:

[0062] ln(DO·Chl a )

[0063] This calculated value reflects the photosynthetic activity of phytoplankton and the concentration of dissolved oxygen in the water. Taking the logarithm of the product is done to compress the numerical range, making it more suitable for analysis. Then, the nitrate concentration in the water is further analyzed. The calculation is performed, and its formula is as follows:

[0064]

[0065] This calculated value is the nitrate concentration. Adding the reciprocal of the square root of the constant allows the formula to make appropriate adjustments to the nitrate concentration through square root calculations; the purpose of adding this is to prevent... When the value is zero, the denominator becomes zero;

[0066] By selecting watersheds within the study area and systematically collecting river water samples and surrounding soil samples, the physicochemical properties of the samples, dissolved oxygen concentration, chlorophyll a concentration, nitrate concentration, and isotopic characteristics, including nitrogen isotope ratio δ, were analyzed. 15 The ratio of N to oxygen isotopes δ 18 The test is conducted to measure dissolved oxygen concentration, which reflects the health status of the water body and the function of the ecosystem; chlorophyll a concentration indirectly assesses the eutrophication level of the water body through phytoplankton photosynthetic activity; and nitrate concentration indicates the pollution level of the water body that agricultural runoff or domestic sewage may have on the water body. Combining the data of these indicators, we can make a preliminary assessment of the ecological characteristics of nitrogen pollution in the watershed and the water quality status.

[0067] Stable isotope tracing technology was used to analyze the main sources and potential transformation processes of nitrate in rivers, through stable isotope δ¹⁸O. 15 N and δ 18 The ratio of O can accurately distinguish various potential nitrogen sources such as agricultural runoff, domestic sewage, precipitation and soil mineralization. In addition, these isotopic features can also capture the transformation pathways of nitrate in the environment, such as denitrification, assimilation and anaerobic ammonia oxidation. Tracer analysis provides quantitative data support for source apportionment, enabling it to effectively locate the source and destination of nitrogen pollution.

[0068] Using the Kirlin diagram To identify the sources and removal characteristics of nitrate concentration in rivers, firstly, a linear Kirchner plot indicates that nitrate concentration in rivers has two main sources: agricultural runoff and domestic sewage. Secondly, a curved Kirchner plot indicates that a mixed or significant nitrate removal process has occurred in the river. and When the linear slope is approximately 1, it indicates the presence of a significant denitrification process; the mixing process is identified by correcting the δ value using a fractionation correction formula, which is expressed as:

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

[0070] Where, δ corr This represents the corrected isotope value, ultimately used to analyze the source of nitrates; δ obs This represents the observed isotope value, i.e., the experimentally measured data; C NO3- The current concentration of nitrate in the water is represented by C0; the initial nitrate concentration is represented by C0; and λ is the fractionation coefficient, representing the degree of isotopic change of nitrate under biological action. This is analyzed... and A linear relationship between the two, with a slope close to 1, further indicates that significant nitrogen removal processes have occurred in the watershed. These processes may include assimilation, denitrification, or anaerobic ammonium oxidation. Based on this, nitrate ion concentrations can be further assessed by considering environmental parameters such as dissolved oxygen and chlorophyll a. The relative importance of removal pathways; next, based on the individual nitrate ions in the river. Sources, specific δ values ​​of precipitation and sewage 15 N / The eigenvalue range is used to determine the potential endmembers affecting river isotope values, especially for those with significant nitrate ion content. In the removal process, isotope fractionation needs to be considered, and the isotope values ​​should be corrected to the initial state based on the fractionation trend regression line.

[0071] Using nitrogen isotope δ 15 N / δ 18 O-labeled nitrates, As a key indicator, it can accurately identify nitrogen sources in rivers and environmental systems. Through stable isotope analysis models, it can quantify the contribution ratio of different nitrogen sources to nitrate concentration in water bodies. Combined with data, it can clearly show the dynamic process of nitrogen cycle in complex environments. In addition, through the combined application of isotope tracing technology and membrane inlet mass spectrometry technology, it can directly measure the rate of denitrification and anaerobic ammonium oxidation in environmental samples, sediments and soil.

[0072] The corrected isotope data were quantitatively source-analyzed using a stable isotope analysis model to quantify individual nitrate ions. Sources of nitrate ions in rivers The contribution ratio of all sources is considered; its stable isotope analysis model is based on a 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%. Its isotope mixing model is expressed as:

[0073]

[0074] Among them, X ijLet P represent the value of the j-th isotope in the i-th water sample, where i = 1, 2, ..., N, and further, j = 1, 2, ..., j; k Let represent the contribution rate of the k-th nitrogen source, and satisfy . The typical isotopic characteristics and their variation formulas from various sources are as follows:

[0075]

[0076] Among them, S jk Let the j-th isotope characteristic value of the k-th nitrogen source be denoted by μ, and follow a mean of μ. jk variance is The normal distribution describes the typical isotopic characteristics and their range of variation from each source; when the shift is caused by denitrification or assimilation, the isotopic fractionation effect coefficient is compensated for by the S... jk The fractionation coefficient is expressed by the following formula after calibration of isotopic characteristic values:

[0077]

[0078] Among them, C jk Let represent the fractionation coefficient of the j-th isotope from the k-th nitrogen source, which follows a mean of λ. jk variance is The normal distribution of C; jk Used to correct S jk The value of is used to compensate for the isotope fractionation effect; error compensation is added to ensure the overall accuracy of the model, and its error compensation formula is:

[0079]

[0080] Where, ε ij Represents the residual, indicating the effect of unmodeled factors on the observed value X. ij The effect, based on its average value μ k and variance ω k Determined; by its average value λ k and variance τ k Decision; ε ij represents the residual term, and represents the unquantified variance, usually set to 0. Through further analysis of these parameters, the mixture model can quantitatively resolve nitrate ion content in different rivers. Analysis of the source of nitrate ions in rivers The contribution of S to the analysis of nitrogen sources in water bodies, thus providing a basis for the determination of nitrogen sources in water bodies. jk Define the isotopic characteristic range for each nitrogen source as input data for the model; P k It is the contribution rate of each nitrogen source, controlling each S jk The weighting effect; Cjk Used to correct S jk To make isotopic characteristic values ​​more consistent with actual chemical processes, and ε ij To ensure the model has a certain degree of flexibility to accommodate uncontrollable biases in the data; its isotope mixing model uses S jk C jk and ε ij The distribution assumptions of S address the differences in source characteristics in isotope mixing models. jk It captures the uniqueness of each nitrogen source, C jk Using the fractionation effect to correct eigenvalues ​​makes the results closer to reality, increasing statistical accuracy, ε ij To compensate for the bias of unmodeled factors, a stable isotope mixing model was used to quantitatively analyze the contribution rate of nitrogen sources based on corrected isotope data. The model is based on a Bayesian framework and uses the Dirichlet distribution as the logistic prior distribution to ensure that the sum of the contribution rates of all nitrogen sources is 100%.

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

[0082] Prepare seven 12mL headspace bottles, add 2g of fresh soil and mix with helium-treated deionized water at a ratio of 1:5;

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

[0084] After the pre-culture was completed, 15N isotope-labeled nitrate was added to 6 of the headspace vials to make its concentration 100 μmol N / L, and the reaction was terminated with 7 mol / L saturated zinc chloride.

[0085] The total formation rate of 29N2 and 30N2 in the sample was determined using a membrane inlet mass spectrometer. The formula for the combined contribution of denitrification and nitrification is as follows:

[0086] P 29 =D 29 +A 29

[0087] Among them, P 29 The rate of N2 gas formation in the sample is expressed in micromoles of nitrogen per kilogram per hour; D 29 The rate at which 29N2 is generated during denitrification is expressed in micromoles of nitrogen per kilogram per hour; A 29 The rate at which 29N2 is generated during anaerobic ammonium oxidation is represented; the rate of 29N2 gas generation P in the sample is measured using a formula. 29 It can be decomposed into the contribution D of denitrification. 29 Contribution of anaerobic ammonium oxidation A 29The sum; using the proportions of different isotopes 15N and 14N in the sample, the rate D of 29N2 gas generated during denitrification was calculated. 29 The formula for the rate of 29N2 formation from 15N and 14N gases is:

[0088]

[0089] Among them, P 30 This indicates the rate of 30N2 gas generation measured in the sample; F N This indicates the proportion of 15N in nitrates; This represents the proportion of 14N in nitrates; by combining the formation rates of 29N2 and 30N2, the total denitrification rate is calculated, and the contribution of denitrification to the total N2 formation rate is expressed by the following formula:

[0090] D t =D 29 +2×P 30

[0091] Among them, D 29 This represents the rate at which 29N2 is generated during denitrification; 2×P 30 This represents twice the rate at which 30N2 gas is produced during denitrification; the total denitrification rate D is calculated by combining the production rates of 29N2 and 30N2. t The formula is used to quantify the overall contribution of denitrification; the contribution of nitrification to the 29N2 formation rate is expressed as:

[0092] A 29 =P 29 -D 29

[0093] Among them, P 29 P represents the generation rate of 29N2 gas in the sample. 30 D represents the measured rate of N2 gas generation in the sample. 29 This indicates the rate at which 29N2 is generated during denitrification; via D 29 and A 29 The calculations quantified the rate contributions of denitrification and anaerobic ammonium oxidation to nitrogen formation, identifying the sources of nitrogen pollution and the efficiency of nitrogen removal in rivers. The contributions of denitrification and nitrification to N2 formation were expressed by the following formulas:

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

[0095] At =P 29 -D t

[0096] Among them, P 29 P represents the generation rate of 29N2 gas in the sample. 30 Indicates the measured rate of N2 gas generation in the sample; A t The contribution of nitrification to the overall N2 formation rate; D t The contribution of denitrification to the total N2 formation rate, including the formation rates of 29N2 and 30N2; F N This indicates that 15N is in the total The proportion of 29N2 and 30N2, and the enrichment of isotopic labels; through the generation rates of 29N2 and 30N2, and the proportion of 15N F N The rates of denitrification and anaerobic ammonium oxidation can be separated and calculated; by separating and quantifying the contributions of denitrification and anaerobic ammonium oxidation to nitrogen production, P can be experimentally determined. 29 P 30 F N After setting the parameters, the nitrogen generation rate for each process was calculated. These rates were further used to analyze the sources and transformation processes of nitrogen pollutants in the river, particularly during denitrification and anaerobic ammonium oxidation. and When converted into nitrogen (N2), different combinations of N2 are formed depending on the degree of isotopic enrichment, such as 29N2 and 30N2. If the formation rate of 30N2 is higher, it indicates that denitrification is dominant, because this process relies more on the two 15NO3 atoms. - The binding of molecules;

[0097] To further verify the accuracy of the nitrogen pollution source apportionment model, a simulated mud mixing system was constructed. The specific operation was as follows: 2g of fresh soil was added to seven 12mL headspace bottles, and deionized water was mixed at a ratio of 1:5. The mixture was pre-cultured in a constant temperature shaker at 200rpm for 72 hours. Subsequently, 15N isotope-labeled nitrate solution with a concentration of 100μmolN / L was added to six headspace bottles, and the reaction was terminated with 7mol / L saturated zinc chloride. The generation rates of 29N2 and 30N2 gases in the system were measured by membrane inlet mass spectrometry. By simulating the rates of denitrification and anaerobic ammonia oxidation in soil or sediment, reliable microscopic verification data were provided for the watershed apportionment model.

[0098] The nitrogen source contribution rate is quantified by combining an isotopic mixing model to ensure the accuracy of the model. The formula for calculating the nitrogen source contribution rate is as follows:

[0099]

[0100] Among them, Pk This represents the contribution rate of the k-th nitrogen source; This indicates summation over all samples; This indicates a product of multiple isotope values ​​for each sample. (X ij |C jk ·S jk ) represents summing over all k nitrogen sources; X ij C represents the value of the j-th isotope in the i-th water sample; jk S represents the fractionation coefficient of the j-th isotope from the k-th nitrogen source; jk This represents the characteristic value of the j-th isotope of the k-th nitrogen source; The likelihood function represents the degree of matching between the observed data and the hypothesized model; N represents the number of samples; K represents the type of nitrogen source; and J represents the type of isotope. A nitrogen source contribution rate calculation model is used to quantitatively calculate the impact of different nitrogen sources—precipitation, wastewater, and agricultural runoff—on nitrate ions in rivers. The contribution ratio is determined by inputting the isotope ratio X of the observed sample. ij and the characteristic value S of each nitrogen source jk Combined with the fractionation coefficient C jk The contribution rate of each nitrogen source was estimated to ensure the accuracy of the model.

[0101] The good agreement between the model's predicted values ​​and observed values ​​is verified using the residual formula, which is as follows:

[0102]

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

[0104] By combining multiple technologies, this approach addresses the shortcomings of existing techniques in nitrogen source apportionment, such as insufficient accuracy and large variability in conversion coefficients. Traditional methods often struggle to effectively distinguish major pollution sources in complex mixed nitrogen source environments and are susceptible to parameter fluctuations in quantitative analysis, leading to biased results. Through isotopic labeling and dynamic tracking, combined with quantitative analysis of multi-source contribution rates, the accuracy and reliability of nitrogen source apportionment can be significantly improved. Particularly under complex conditions of mixed nitrogen sources, this approach can effectively identify major pollution contributors and provide clear source apportionment results.

[0105] Compared with traditional methods, firstly, δ 15 N / δ 18The unique properties of the O isotope distinguish different nitrogen sources such as agricultural runoff, domestic sewage, and precipitation, providing a clear source. Secondly, by introducing a stable isotope analysis model, the isotope data is combined with probability distribution to ensure more accurate analysis of nitrogen source proportions. Finally, the membrane inlet mass spectrometer directly measures the rates of denitrification and anaerobic ammonia oxidation, breaking through the limitations of traditional methods that indirectly estimate reaction rates, thereby further revealing the key links in the nitrogen cycle process.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes, characterized in that, Includes the following steps: The watershed to be studied was selected, and river water and soil samples were systematically collected within the watershed. The collected samples were analyzed for physicochemical and isotopic properties. The test was conducted; a stable isotope tracing system and method were used to analyze and identify the main sources of nitrate in rivers and their potential transformation processes; a simulated mud mixing system was constructed and 15N isotope labeling was added to it to determine the rates of denitrification and anaerobic ammonium oxidation processes in soil or sediment; the results of river source apportionment were compared with those of soil or sediment in the microenvironment. The conversion process rate was compared to verify the accuracy of the nitrogen source apportionment model; Gearing plots were used. To identify the sources and removal characteristics of nitrate concentration in rivers, a linear Killerlin plot indicates two sources of nitrate concentration in the river; a curved Killerlin plot indicates multi-source mixing or a significant nitrate removal process. The mixing process can be identified by correcting the δ value using a fractionation correction formula, which is expressed as follows: in, This indicates the corrected isotope value; Indicates the observed isotope value; This indicates the current concentration of nitrates in the water; This represents the initial nitrate concentration. The fractionation coefficient is used; the corrected isotope data are quantitatively source-analyzed using a stable isotope analysis model to quantify individual nitrate ions. Sources of nitrate ions in rivers The contribution ratio; its stable isotope analysis model is based on a Bayesian framework and establishes a logical prior distribution on the Dirichlet distribution. The formula for its isotope mixing model is: in, Indicates the first The first water sample Isotope values; Indicates the first The contribution rate of each nitrogen source; the typical isotopic characteristics of each source and their variation formulas are as follows: in, Indicates the first The first nitrogen source Individual isotopic characteristic values; when the shift is caused by denitrification or assimilation, the isotopic fractionation effect coefficient is compensated for. The fractionation coefficient is expressed by the following formula after calibration of isotopic characteristic values: in, Indicates the first The first nitrogen source Each isotope fractionation coefficient; error compensation is added to ensure the overall accuracy of the model, and the error compensation formula is: in, Residuals represent the effect of unmodeled factors on the observed values. The impact.

2. The method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 1, characterized in that: The specific procedures for the mud mixing system include: preparing seven 12mL headspace bottles, adding 2g of fresh soil, and mixing it with helium-treated deionized water at a 1:5 ratio; pre-culturing in a constant-temperature shaker at 200rpm and sample temperature for 72 hours; after the pre-culturing, adding... Isotope-labeled nitrates to a concentration of 100 μmol N / L, and the reaction was terminated with 7 mol / L saturated zinc chloride; the concentration of nitrates in the sample was determined using a membrane inlet mass spectrometer. and The total formation rate is contributed by both denitrification and nitrification, as shown in the following formula: in, Indicating the sample The rate of gas formation; This indicates the products generated during the denitrification process. The rate; This indicates the product generated during anaerobic ammonium oxidation. The rate; its and Gas generation The generation rate formula is: in, Indicates the measured values ​​in the sample Gas generation rate; This indicates that it is in nitrates The proportion; Indicates nitrates The ratio; its denitrification effect on The formula for the contribution of the total generation rate is expressed as: in, This indicates the products generated during the denitrification process. The rate; Indicates the product generated by denitrification Twice the gas velocity; its nitration effect on The formula for expressing the contribution of generation rate is: in, Indicating the sample The rate of gas formation; Indicates the measured values ​​in the sample Gas generation rate; This indicates the products generated during the denitrification process. The rate; among which, denitrification and nitrification have a significant impact on... The formula for generating contribution is expressed as: in, Indicating the sample The rate of gas formation; Indicates the measured values ​​in the sample Gas generation rate; For nitration Contribution to the overall generation rate; For denitrification Contribution to the overall generation rate; express In total The proportion in.

3. The method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 2, characterized in that: The nitrogen source contribution rate is quantified by combining an isotopic mixing model to ensure the accuracy of the model. The formula for calculating the nitrogen source contribution rate is as follows: in, Indicates the first The contribution rate of each nitrogen source; Indicates the first The first water sample Isotope values; Indicates the first The first nitrogen source Isotope fractionation coefficient; Indicates the first The first nitrogen source Isotopic eigenvalues; It is the likelihood function; Indicates the number of samples; Indicates the type of nitrogen source; Indicates the type of isotope.

4. The method for source apportionment of river nitrogen pollutants based on watershed nitrogen turnover and isotopes according to claim 3, characterized in that: The good agreement between the model's predicted values ​​and observed values ​​is verified using the residual formula, which is as follows: in, This represents the error check value; Indicates the first Observations for each sample; Indicates the first Predicted values ​​for each sample; Indicates the number of samples.

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