Water body phosphorus pollution source analysis method and system based on conservative tracer ion and oxygen isotope combined tracing

Abstract

The present application belongs to the technical field of water environment protection, and particularly relates to a water body phosphorus pollution source analysis method and system based on conservative tracer ions and oxygen isotope combined tracing, which determines the concentrations of conservative tracer ions such as chlorine ions and bromine ions and the oxygen isotope composition of phosphates in water samples in a target water area, constructs a combined tracing model for quantitative source analysis. The water volume contribution ratio of each potential pollution source is determined through end member mixing analysis; based on the oxygen isotope composition of phosphates and the pre-built isotope fingerprint spectrum of pollution sources, the phosphorus load contribution rate is calculated through a Bayesian mixture model; and the phosphorus load contribution rate is jointly constrained and cross-verified by the water volume contribution ratio to obtain a revised contribution rate. The present application verifies and revises the Bayesian mixture model output of the oxygen isotope of phosphates based on the water volume contribution determination result of the conservative tracer ions, thereby avoiding misjudgment of the source contribution caused by isotope fractionation effects such as adsorption, precipitation and biological absorption in the phosphorus migration process.

Description

Technical Field

[0001] This invention belongs to the field of water environmental protection technology, specifically relating to a method and system for source analysis of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes. Background Technology

[0002] Phosphorus is a key limiting element causing eutrophication in lakes, and accurate identification of phosphorus pollution sources is a prerequisite for precise watershed management. Among existing technologies, phosphate oxygen isotope tracing technology has become an important means of tracing phosphorus pollution sources. Its principle lies in the fact that phosphorus from different sources undergoes different biogeochemical processes during formation and transformation, leading to variations in the oxygen isotope ratio in phosphate ions. Different fingerprint characteristics are exhibited, which can be used to distinguish pollution sources such as agricultural fertilizers, domestic sewage, and industrial wastewater. Related technical solutions (such as Chinese invention patent CN121919507A) further combine phosphate oxygen isotopes with water body hydrogen and oxygen isotopes, phosphorus concentration, etc., into multidimensional tracer factors. Combined with Bayesian mixture models, this achieves quantitative analysis of the contribution rate of phosphorus pollution in each sub-basin within the watershed, and further refines the contribution rate to different land use types using microbial functional gene abundance tracer technology.

[0003] However, the aforementioned existing technologies still have the following drawbacks: On the one hand, after phosphates enter water bodies, they are easily adsorbed by particulate matter, absorbed by aquatic organisms, or precipitated. During their migration, isotope fractionation may occur, leading to variations in measured values. The values ​​deviate from the true isotopic characteristics of the original source, affecting the accuracy of source tracing; on the other hand, existing methods mostly rely on a single tracer system and lack cross-validation between different tracer mechanisms, making it difficult to effectively distinguish pollution sources with similar isotopic characteristics under complex hydrological conditions, resulting in insufficient reliability and stability of source tracing results. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for analyzing phosphorus pollution sources in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes, in order to solve the technical problem in existing phosphorus pollution source tracing of lakes that relies on a single tracer and is susceptible to biochemical interference during phosphorus migration, making it impossible to accurately quantify the contribution rate of multiple pollution sources.

[0005] The present invention achieves the above objectives through the following technical solutions: Firstly, this invention proposes a method for source apportionment of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes, the method comprising: In response to a request for phosphorus pollution source tracing in a target water area, a preset phosphorus source isotope fingerprint spectrum is obtained, and the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected at each section of the target water area are determined; the conservative tracer ions include at least one of chloride ions and bromide ions. Based on the conservative tracer ion concentration and phosphate oxygen isotope composition, a conservative ion-isotope joint tracer model is constructed to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area. The joint tracer model uses endmember mixing analysis of conservative tracer ions to determine the water contribution ratio of each potential pollution source, and then uses the water contribution ratio to constrain the isotope mixing model based on the isotope fingerprint to quantitatively analyze the phosphorus load contribution rate of each potential pollution source.

[0006] Furthermore, the sampling sections include river sections flowing into the lake, lake sections, and groundwater monitoring well sections; The cross-sections of the rivers flowing into the lake are set upstream of the entrances of each river into the target water area, and three sampling depths—surface, middle and bottom—are set on the same cross-section. The cross-sections within the lake are set up using a grid-based sampling method based on the shape and size of the target water area. In areas with stratification, at least one sampling point is set up in each of the surface, thermocline, and bottom layers. The groundwater monitoring well sections are arranged along the shoreline of the target water area.

[0007] Furthermore, the phosphorus-derived isotope fingerprint is established through the following steps: Representative end-member samples of each potential phosphorus pollution source are obtained. The end-member samples are samples that can characterize the isotopic features of the pollution source. The potential phosphorus pollution sources include at least two of the following: agricultural non-point sources, domestic sewage sources, industrial wastewater sources, and lake sediment release sources. The phosphate oxygen isotope characteristic values ​​of each end-member sample were determined; based on the end-member samples and their corresponding isotope characteristic values, the isotope fingerprint spectrum was constructed.

[0008] Furthermore, the determination of the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected from each section of the target water area includes: The concentration of the conservative tracer ions was determined by ion chromatography or electrochemical detection. The conservative tracer ions are those whose concentration changes in water are dominated by physical dilution and mixing. Phosphate in the water sample was extracted into silver phosphate solid using silver salt precipitation. The silver phosphate solid was then thermally decomposed into carbon monoxide gas. The carbon monoxide gas was analyzed by delta-isotope ratio mass spectrometry. 18The oxygen isotope composition of the phosphate was obtained by measuring the O value.

[0009] Furthermore, the construction of the conservative ion-isotope joint tracing model includes: Based on the aforementioned conservative tracer ion concentration, let the conservative ion concentration vector of each potential pollution source be... The conservative ion concentration vector of the mixed water body is By solving the mixed constraint equations = ,and , Determine the water volume contribution ratio of each potential pollution source. ; Based on the phosphate oxygen isotope composition and the j-th pollution source end-member in the isotope fingerprint spectrum Eigenvalues By using a Bayesian mixture model and employing the Markov chain Monte Carlo method for parameter estimation, the mixture equations are solved. Calculate the phosphorus load contribution rate of each potential pollution source. ,in For the actual measurement of mixed samples value, This is the model error term; Based on the aforementioned water contribution ratio Contribution rate of the phosphorus load Joint constraint optimization was performed to obtain the corrected phosphorus load contribution rate of each potential pollution source.

[0010] Furthermore, the water volume contribution ratio is... Contribution rate of the phosphorus load Joint constraint optimization was performed to obtain the corrected phosphorus load contribution rates of each potential pollution source, including: The water volume contribution ratio The phosphorus contribution of water volume is obtained by weighting the phosphorus concentration of the corresponding pollution source. The water-weighted phosphorus contribution reference value is compared with the phosphorus load contribution rate output by the Bayesian mixture model. Perform a comparison; When the deviation between the two exceeds a preset threshold, the input data of the Bayesian mixture model is verified and corrected, and the corrected phosphorus load contribution rate is recalculated.

[0011] Furthermore, the method also includes: generating a phosphorus pollution source composition map of the target water area based on the contribution rate of each potential phosphorus pollution source obtained by analysis. The source composition map includes at least one of the following: a pie chart of pollution source contribution rate, a phosphorus contribution heat map of the river section flowing into the lake, and a spatiotemporal variation trend map of phosphorus load.

[0012] Secondly, this invention proposes a water phosphorus pollution source apportionment system based on the combined tracing of conservative tracer ions and oxygen isotopes, used to implement the above-mentioned water phosphorus pollution source apportionment method, including: The data acquisition module is used to acquire a preset phosphorus-derived isotope fingerprint spectrum and to determine the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected from each section of the target water area. The model building module is used to construct a conservative ion-isotope joint tracer model based on the conservative tracer ion concentration and phosphate oxygen isotope composition. The source analysis module is used to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area through the joint tracer model. The model building module includes: The end-member mixing analysis unit is used to determine the water volume contribution ratio of each potential pollution source based on the conservative tracer ion concentration. An isotope mixing analysis unit is used to calculate the phosphorus load contribution rate of each potential pollution source based on the phosphate oxygen isotope composition and the isotope fingerprint spectrum. A joint constraint unit is used to constrain and optimize the phosphorus load contribution rate based on the water volume contribution ratio.

[0013] Furthermore, the data acquisition module includes a conservative ion detection unit, which includes an ion chromatography analysis subunit and a data processing subunit; the ion chromatography analysis subunit is used to detect the concentrations of chloride ions and bromide ions, and the data processing subunit is used to calculate the concentration values ​​of each ion based on the ion chromatography peak area and generate a sampling point-ion concentration comparison table. The data acquisition module includes an isotope analysis unit, which comprises a phosphate extraction subunit, a high-temperature thermal conversion subunit, and an isotope ratio mass spectrometry subunit. The phosphate extraction subunit extracts phosphate from the water sample into silver phosphate solid using silver salt precipitation. The high-temperature thermal conversion subunit thermally decomposes the silver phosphate solid into carbon monoxide gas at 1450°C. The isotope ratio mass spectrometry subunit analyzes the δ¹⁸O values ​​of the carbon monoxide gas. 18 The O value was measured.

[0014] Furthermore, it also includes a sampling deployment module for obtaining the sampling cross-section setting information of the target water area and its surrounding catchment area; the sampling cross-section includes the cross-section of the river flowing into the lake, the cross-section inside the lake, and the cross-section of the groundwater monitoring well.

[0015] The beneficial effects of this invention are as follows: This invention introduces conservative tracer ions as physical mixing tracers to independently verify and constrain the chemical tracing results of phosphate oxygen isotopes, avoiding source contribution misjudgments caused by fractionation effects such as adsorption, precipitation, and bioabsorption during phosphorus migration in single isotope methods. The concentration changes of conservative tracer ions are controlled only by physical dilution mixing, and their end-member mixing analysis can determine the water volume contribution ratio of each potential pollution source. Based on this, the phosphorus load contribution rate output by the isotope mixing model is cross-compared, and the model input is validated and corrected when the deviation exceeds expectations. This method combines physical mixing information with chemical characteristic information, enabling cross-validation of source tracing results from two independent dimensions, overcoming the insufficient reliability of traditional single tracer methods under complex hydrological conditions. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the main process of the water phosphorus pollution source analysis method in this embodiment of the invention. Figure 2 This is a flowchart illustrating the construction of the conservative ion-isotope joint tracing model in an embodiment of the present invention. Figure 3 This is a system block diagram of the water phosphorus pollution source apportionment system in an embodiment of the present invention. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0018] Example 1

[0019] This embodiment uses a typical shallow lake in eastern my country as the target water area to provide a detailed description of the water phosphorus pollution source apportionment method based on the combined tracing of conservative tracer ions and oxygen isotopes proposed in this invention. The lake has a water area of ​​approximately 150 km². 2 With an average depth of 2.5 m, it is a typical eutrophic lake, with total phosphorus concentration consistently ranging from 0.15 to 0.45 mg / L, significantly exceeding the Class III water quality limit stipulated in the Surface Water Environmental Quality Standard. The total catchment area of ​​the lake is approximately 3500 km². 2 The land use types in the region are mainly agricultural land (accounting for approximately 55%), urban construction land (accounting for approximately 25%), and forest land (accounting for approximately 20%). The main potential sources of phosphorus pollution in the catchment area include agricultural non-point source pollution, domestic sewage pollution, industrial wastewater pollution, and release from sediments within the lake.

[0020] A specific embodiment of this invention proposes a method for analyzing phosphorus pollution sources in water bodies based on the joint tracing of conservative tracer ions and oxygen isotopes. The method includes: responding to a phosphorus pollution source tracing request in a target water area, acquiring a preset phosphorus source isotope fingerprint spectrum, and measuring the concentration of conservative tracer ions, phosphorus concentration data, and phosphate oxygen isotope composition in water samples collected at each section of the target water area; the conservative tracer ions include at least one of chloride ions and bromide ions, and the phosphorus concentration data includes at least one of dissolved total phosphorus and total phosphorus; based on the conservative tracer ion concentration and phosphate oxygen isotope composition, constructing a conservative ion-isotope joint tracing model to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area; wherein, the joint tracing model uses end-member mixing analysis of conservative tracer ions to determine the water volume contribution ratio of each potential pollution source, and then uses the water volume contribution ratio to constrain the isotope mixing model based on the isotope fingerprint spectrum to quantitatively analyze the phosphorus load contribution rate of each potential pollution source.

[0021] Please see Figure 1 and Figure 2 In specific implementation, the water phosphorus pollution source apportionment method in this embodiment includes the following steps: S1. Recommendation of phosphorus-derived isotope fingerprinting. Before conducting source tracing analysis of the target water area, a phosphorus source isotope fingerprint spectrum covering various potential phosphorus pollution sources in the target water area is established in advance. Specifically, representative end-member samples of each potential phosphorus pollution source are obtained. The end-member samples are samples that can characterize the isotopic features of the pollution source. The potential phosphorus pollution sources include agricultural non-point sources, domestic sewage sources, industrial wastewater sources, and in-lake sediment release sources.

[0022] As an example, the collected end-member samples included: influent and effluent water samples from 8 sewage treatment plants in the catchment area, which can reflect the characteristics of domestic sewage sources; industrial wastewater samples from 17 phosphorus-related enterprises, which can reflect the characteristics of industrial wastewater sources; 42 farmland runoff and soil leachate water samples representing different farmland types and fertilization levels, which can reflect agricultural non-point source characteristics; and 10 pore water samples from lake columnar sediments, which can reflect endogenous release characteristics.

[0023] Phosphate was extracted from each end-member sample using silver salt precipitation: A suitable amount of filtered water sample was taken, and the pH was adjusted to 7.5-8.5 with NaOH solution. Silver nitrate solution was slowly added under stirring to allow phosphate ions to react with silver ions to form silver phosphate precipitate. The precipitate was then aged in a 60℃ water bath, collected by centrifugation, and washed with deionized water to remove impurities. The purified silver phosphate precipitate was dried to constant weight at 60℃ to obtain a solid silver phosphate sample. The solid silver phosphate was placed in a high-temperature thermal conversion elemental analyzer and thermally decomposed at 1450℃. Oxygen atoms in the phosphate group combined with carbon atoms to generate carbon monoxide gas. The generated carbon monoxide gas was then sent to an isotope ratio mass spectrometer via a helium carrier gas for further analysis. Value determination, based on the international standard VSMOW isotopic composition determination. The value is expressed as a percentage (in thousands).

[0024] The phosphate oxygen isotope characteristic values ​​of each potential phosphorus pollution source end-member were determined and are shown in Table 1.

[0025] Table 1. δ values ​​of each potential phosphorus pollution source end-member 18 O-PO4 eigenvalues ​​(‰)

[0026] Table 1 shows that the δ values ​​of different types of phosphorus pollution sources 18 O-PO4 values ​​exhibit a distinct differential distribution pattern: industrial wastewater end-members Overall, the values ​​were relatively high (14.2‰~23.5‰), with farmland non-point source end-members in the middle range (9.2‰~15.6‰) and sediment pore water end-members the lowest (8.5‰~12.8‰). This difference stems from the varying environmental conditions and biogeochemical processes experienced by phosphate ions in different pollution sources. Phosphates generated in high-temperature industrial environments tend to have higher phosphate content. The value is positive, while the endogenous phosphorus in sediments that have undergone long-term microbial cycling and isotopic fractionation shows a negative value. The aforementioned differences provide an effective fingerprinting basis for subsequent isotopic mixing models. Based on the above measurement results, a correspondence between each potential phosphorus pollution source and its isotopic characteristic value is established, forming the phosphorus source isotopic fingerprint spectrum.

[0027] S2. Set up data collection sections and measure relevant data. In response to the request for phosphorus pollution source tracing in the target water area, the aforementioned preset phosphorus source isotope fingerprint spectrum was obtained, and the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected from each section of the target water area were determined.

[0028] Preferably, the sampling sections include river sections flowing into the lake, lake sections, and groundwater monitoring well sections. River sections flowing into the lake are set upstream of the entrances of each river into the target water area, and three sampling depths (surface, middle layer, and bottom layer) are set on the same cross section. Lake sections are set according to the shape and size of the target water area, using a grid-based sampling method, and at least one sampling point is set in each of the surface, thermocline, and bottom layers in areas with stratification. Groundwater monitoring well sections are arranged along the shoreline of the target water area.

[0029] (1) Collection section layout The sampling sections include three categories: river sections flowing into the lake, lake body sections, and groundwater monitoring well sections. The river sections flowing into the lake are set up as follows: for each of the seven main rivers flowing into the lake within its catchment area, a sampling section is set up within 500-1000m upstream of the inlet. Each sampling section uses the river centerline as a reference, with one sampling point each on the left bank, center, and right bank. At each sampling point, three sampling depths are set on the same cross-section: surface (0.3 m), middle (1.0 m), and bottom (0.5 m from the bottom sediment). Portable stainless steel water samplers are used to collect water samples in stratified layers. The lake body sections are set up as follows: based on the shape and size of the target lake, a grid-based sampling method is used, with a basic spacing of 1 km × 1 km, setting up 25 sampling points throughout the lake. Because the lake is generally shallow and does not exhibit significant temperature stratification, water samples are collected at two depths at each sampling point: surface (0.5 m) and bottom (0.5 m from the bottom sediment). The groundwater monitoring well section is set up as follows: within 500 m from the shoreline, 12 shallow groundwater monitoring wells are arranged at approximately equal intervals along the circumference of the lake. The depth of each monitoring well is 3 to 5 m, ensuring that it penetrates the water table and enters the saturated aquifer. The sampling depth is 1 to 2 m below the groundwater level, and peristaltic pumps are used to collect groundwater samples.

[0030] All water samples were collected once each during the high-water season, from June to August, and during the low-water season, from December to February, to assess the impact of seasonal variations on phosphorus source identification results.

[0031] (2) Determination of conservative tracer ion concentration Conservative tracer ions include chloride ions (Cl... - ) and bromide ions (Br - Conservative tracer ions are ions whose concentration changes in water are dominated by physical dilution and mixing. Their concentration is controlled only by physical dilution and mixing and is not significantly affected by biological activities, chemical reactions, and adsorption and precipitation in the water. Therefore, they can be used as ideal tracer indicators to reflect the mixing and migration patterns of water bodies.

[0032] The concentration of conservative tracer ions was determined using ion chromatography. The specific steps included: irradiating the collected water sample with 0.45... After filtration through a membrane, the sample is injected into an ion chromatography system equipped with an anion exchange column and a conductivity detector. The eluent is KOH solution, the flow rate is 1.0 mL / min, the column temperature is controlled at 30℃, and the injection volume is 25 mL. According to Cl - and Br - The retention time is used to qualitatively determine the ion species, and the Cl- concentration is calculated based on the relationship between the peak area of ​​the ion chromatography and the standard solution. - and Br - The concentration values ​​were calculated, and a sampling point-ion concentration comparison table was generated. Blank and parallel samples were included for each batch of samples to ensure the accuracy and precision of the analytical results.

[0033] The measurement results show that the Cl in the river water flowing into the lake - The concentration range was 15.8–64.3 mg / L, Br - The concentration range was 0.08~0.45 mg / L; the Cl concentration in the lake water was... - The concentration range was 22.6–48.5 mg / L, Br - Concentration range: 0.11~0.32 mg / L; Cl in groundwater - The concentration range was 12.3–38.7 mg / L, Br - The concentration range was 0.04–0.21 mg / L; the concentrations of conservative tracer ions varied significantly among water sources.

[0034] (3) Determination of phosphate oxygen isotope composition and phosphorus concentration data The determination of the oxygen isotope composition of phosphate was performed using the same method as the determination of the end-member sample in step S1. Specifically, silver salt precipitation was used to extract phosphate from the water sample into solid silver phosphate. The solid silver phosphate was then thermally decomposed at 1450℃ to convert it into carbon monoxide gas. The carbon monoxide gas was then analyzed using isotope ratio mass spectrometry. The oxygen isotope composition of the phosphate was obtained by measuring the values.

[0035] In addition, phosphorus concentration data for water samples collected at each cross-section were determined, including dissolved total phosphorus and total phosphorus. Total phosphorus was determined according to national standard methods. In an acidic medium, potassium persulfate was used to oxidize phosphorus-containing compounds in the water sample to phosphate, which then reacted with ammonium molybdate to form phosphomolybdic acid. After reduction with ascorbic acid, the absorbance was measured at a wavelength of 700 nm, and the total phosphorus concentration was calculated using a standard curve.

[0036] The results showed that the total phosphorus concentration in the rivers flowing into the lake ranged from 0.12 to 0.58 mg / L, with an average of 0.31 mg / L; the total phosphorus concentration in the lake itself ranged from 0.15 to 0.45 mg / L, with an average of 0.28 mg / L; and the total phosphorus concentration in the groundwater ranged from 0.02 to 0.08 mg / L, with an average of 0.04 mg / L. The phosphorus concentration data from each sampling point were used as the mass-weighted input for the subsequent isotope mixing model.

[0037] S3. Constructing a conservative ion-isotope joint tracing model Based on the concentration of conservative tracer ions and the oxygen isotope composition of phosphate, a conservative ion-isotope joint tracer model is constructed to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area. The joint tracer model uses end-member mixing analysis of conservative tracer ions to determine the water volume contribution ratio of each potential pollution source. Then, the water volume contribution ratio is used to constrain the isotope mixing model based on isotope fingerprinting to quantitatively analyze the phosphorus load contribution rate of each potential pollution source.

[0038] Combination Figure 2 The specific steps for constructing a conserved ion-isotope joint tracing model are as follows: Step 1: End-member mixing analysis based on conservative tracer ions. Utilizing the spatial differences in the concentrations of conservative tracer ions, an end-member mixing analysis model was employed to determine the water volume contribution ratio of each potential pollution source. Seven representative river sections with relatively severe pollution and high phosphorus concentrations flowing into the lake were selected as source-end-member analysis objects, representing the following three types of pollution sources: Category A: River sections dominated by domestic sewage (3 river sections, located downstream of the urban area, Cl) - The average concentration was 58.5 mg / L. Category B: River sections dominated by industrial wastewater (2 river sections, located downstream of the industrial park, Cl) - The average concentration was 48.3 mg / L. Category C: River sections dominated by agricultural non-point source pollution (2 river sections, located in concentrated agricultural areas, Cl) - The average concentration was 32.6 mg / L. (Cl in lake water...) - The average concentration was 38.5 mg / L.

[0039] Let the conservative ion concentration vector of each potential pollution source be... The conservative ion concentration vector of the mixed water body is By solving the mixed constraint equations = ,and , Determine the water volume contribution ratio of each potential pollution source. By solving the above set of linear constraint equations, the contribution ratios of the three types of pollution sources to the lake's water volume were obtained as follows: domestic sewage, which is the dominant source, contributed approximately 32%; industrial wastewater, which is the dominant source, contributed approximately 28%; and agricultural non-point source pollution, which contributed approximately 40%. This ratio reflects the relative importance of the three types of external inputs in the lake's water replenishment.

[0040] Step 2: Isotopic mixing model analysis based on phosphate oxygen isotopes. Using phosphate oxygen isotope data, a Bayesian mixture model is used to calculate the contribution rate of each phosphorus source type to the lake's phosphorus load. Model input parameters include: δ¹⁸O of the mixed sample. 18 O-PO4 values ​​(measured values ​​at various sampling points in the lake body, mean 13.2‰ ± 1.6‰); δ¹⁸O values ​​of each pollution source end-member. 18 O-PO4 characteristic values ​​are shown in Table 1; phosphorus concentration data at each sampling point are used as mass-weighted input; prior information for the discrimination of each pollution source endmember is also included. The parameters of the Bayesian mixture model are set as follows: Markov chain Monte Carlo chain number = 3, iterations per chain = 200,000, aging steps = 50,000, refinement step size = 50. Model convergence is assessed using the Gelman-Rubin diagnostic index (GRI). (This is considered convergence).

[0041] δ 18 O-PO4, as a characteristic chemical fingerprint of phosphorus origin, has the following mixed weighting relationship: ,in For the actual measurement of mixed samples value, For the j-th pollution source end-member Eigenvalues ​​(determined by isotopic fingerprinting). Let be the contribution rate of the j-th phosphorus source to the phosphorus load of the lake. This is the model error term.

[0042] The model results provide the following posterior estimates of the contribution rates of each phosphorus source: agricultural non-point source 38%±8% (95% confidence interval); domestic sewage source 28%±6% (95% confidence interval); industrial wastewater source 15%±5% (95% confidence interval); and lake source 19%±7% (95% confidence interval).

[0043] Step 3: Dual Tracer Joint Constraint Optimization. Based on water contribution ratio. Contribution rate to phosphorus load Joint constraint optimization was performed to obtain the corrected phosphorus load contribution rate of each potential pollution source. Specifically, the water volume contribution ratio was adjusted. A weighted conversion was performed with the phosphorus concentration emitted from the corresponding pollution source to obtain a water volume-weighted phosphorus contribution reference value; this water volume-weighted phosphorus contribution reference value was then combined with the phosphorus load contribution rate output by the Bayesian mixture model. A comparison is performed; when the deviation exceeds a preset threshold, the input data of the Bayesian mixture model is verified and corrected, and the corrected phosphorus load contribution rate is recalculated. The verification and correction specifically include: re-checking the representativeness of the water samples collected from the pollution source corresponding to the deviation, confirming whether the sampling points accurately reflect the inflow characteristics of the pollution source; and reviewing the δ0.05 of the end-member sample of the pollution source. 18 Are there outliers in the O eigenvalue measurement data? Is the standard deviation of the endmember eigenvalues ​​too large, leading to insufficient model discrimination? For pollution sources closely related to water volume, what is their proportion of water volume contribution obtained from conservative ion tracing? It should be compared with its contribution rate of phosphorus The corresponding weights are basically consistent. If the deviation is too large, the end-member characteristic value of the pollution source or the mixed sample data should be re-measured or abnormal data should be removed. Then the Bayesian mixture model should be run again to obtain the corrected phosphorus load contribution rate.

[0044] In one example, after joint constraint optimization, the 32% water volume contribution from domestic sewage was basically consistent with the 28% phosphorus contribution from domestic sewage in isotope tracing, with a deviation of about 4%. The 28% water volume contribution from industrial wastewater differed from the 15% contribution in isotope tracing, indicating that industrial wastewater has a high phosphorus concentration, meaning that the phosphorus content per unit volume is high, so although the water volume share is not high, the phosphorus contribution accounts for a certain proportion. This finding is highly consistent with the actual survey results, where the average total phosphorus concentration of industrial wastewater was 2.8 mg / L, which is significantly higher than the 0.3~0.8 mg / L of other types of emission sources. The 40% water volume contribution from agricultural non-point sources was basically consistent with the 38% phosphorus contribution in isotope tracing, with a deviation of about 2%, verifying the consistency of the results of the two tracing methods and strongly supporting that agricultural non-point sources are the main contributor to phosphorus input to the lake. The 19% phosphorus contribution from endogenous sources could not be directly traced by conservative ions, but it was effectively resolved by the isotope mixing model. By combining the constraints of conservative ions and isotopes, the corrected contribution rates of each pollution source in the lake phosphorus pollution in this embodiment were finally determined as follows: agricultural non-point source 37%~40%, domestic sewage source 26%~30%, industrial wastewater source 12%~18%, and lake endogenous release 16%~22%.

[0045] S4. Results Visualization Based on the contribution rates of each potential phosphorus pollution source obtained from the analysis, a phosphorus pollution source composition map of the target water area is generated. The source composition map includes: a pie chart of phosphorus source composition for the entire lake, which visually displays the contribution rates of the four types of pollution sources; a heat map of phosphorus contribution from each river section flowing into the lake, which displays the interpolation analysis results of 25 lake sampling points as a two-dimensional color contour map superimposed on the lake digital map; and a bar chart comparing the phosphorus pollution contribution rates during the high-water season and the low-water season, revealing the seasonal input differences.

[0046] To verify the accuracy and reliability of the method of this invention, the following cross-validation work was also carried out: Phosphorus load was calculated simultaneously in the same lake using the traditional water quantity-water quality flux method. The results showed that the annual average contribution rates of agricultural non-point sources, domestic sewage sources, and industrial wastewater sources among external inputs calculated by the flux method were 35%, 26%, and 14%, respectively. The method of this invention showed good consistency with the flux method in terms of external input allocation, and additionally resolved the contribution of lake endogenous sources, which is difficult to quantitatively assess using traditional methods. A full-process sampling analysis was performed again after a three-month interval. The absolute value of the deviation between the analysis results of the contribution rates of each pollution source and the first results was less than 5%, demonstrating the good repeatability and stability of the method of this invention.

[0047] According to the above embodiments, the core technical concept of this invention lies in: constructing a dual tracer system using conservative tracer ions and phosphate oxygen isotopes, and jointly analyzing the same target water body through two independent tracer mechanisms. Among them, the conservative tracer ions (Cl... - ,Br - As a physical mixing tracer, the concentration change of phosphorus is only controlled by the physical dilution and mixing of water bodies. End-member mixing analysis can determine the water volume contribution ratio of each potential pollution source. Phosphate oxygen isotopes, as chemical characteristic tracers, can calculate the phosphorus load contribution rate of each pollution source through Bayesian mixture models. Based on this, the phosphorus load contribution rate output by the isotope mixing model is jointly constrained and cross-validated with the water volume contribution ratio. When the deviation between the two exceeds a preset threshold, the input data is verified and corrected. This avoids misjudgment of source contribution caused by isotope fractionation effects such as adsorption, precipitation, and biological absorption during phosphorus migration, transforming the source tracing results from a single chemical fingerprint inference to a quantitative analysis with dual verification of physical mixing information and chemical characteristic information.

[0048] Example 2

[0049] See Figure 3 A water phosphorus pollution source apportionment system based on the combined tracing of conservative tracer ions and oxygen isotopes is disclosed. This system is used to implement the water phosphorus pollution source apportionment method described in Example 1. It includes a data acquisition module, a model building module, and a source tracing module. The data acquisition module acquires a pre-defined phosphorus source isotope fingerprint and measures the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected from various sections of the target water body. The model building module constructs a conservative ion-isotope combined tracing model based on the conservative tracer ion concentration and phosphate oxygen isotope composition. The source tracing module analyzes the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water body using the combined tracing model. The model building module further includes: The end-member mixing analysis unit is used to determine the water volume contribution ratio of each potential pollution source based on the conservative tracer ion concentration. The isotope mixing analysis unit is used to calculate the phosphorus load contribution rate of each potential pollution source based on the phosphate oxygen isotope composition and isotope fingerprint spectrum. The joint constraint unit is used to constrain and optimize the phosphorus load contribution rate based on the proportion of water contribution.

[0050] In a preferred embodiment, the data acquisition module includes a conservative ion detection unit and an isotope analysis unit. The conservative ion detection unit comprises an ion chromatography analysis subunit and a data processing subunit; the ion chromatography analysis subunit is used to detect the concentrations of chloride and bromide ions, and its core components are an anion separation column and a conductivity detector; the data processing subunit is used to calculate the concentration values ​​of each ion based on the correlation between the ion chromatography peak area and the standard solution, and automatically generates a sampling point-ion concentration comparison table. The isotope analysis unit includes a phosphate extraction subunit, a high-temperature thermal conversion subunit, and an isotope ratio mass spectrometry subunit; the phosphate extraction subunit uses silver salt precipitation to extract phosphate from the water sample into solid silver phosphate; the high-temperature thermal conversion subunit thermally decomposes the solid silver phosphate into carbon monoxide gas at 1450℃; the isotope ratio mass spectrometry subunit measures the δ¹⁸O of the carbon monoxide gas. 18 The O value was measured.

[0051] In a preferred embodiment, the system further includes a sampling deployment module for acquiring information on the sampling cross-sections of the target water area and its surrounding catchment area. These cross-sections include river sections flowing into the lake, lake sections, and groundwater monitoring well sections. The sampling deployment module incorporates a digital map and water system information of the target water area, and features intelligent sampling point placement. It can automatically recommend the optimal sampling cross-section layout based on water area shape factors and shoreline characteristics, and works in conjunction with a GPS positioning system to ensure the spatial accuracy of the sampling points on site.

[0052] In a preferred embodiment, the system also includes a visualization module, which displays the contribution rate of each potential phosphorus pollution source output by the source analysis module in the form of a map overlay, and dynamically marks the contribution ratio and trend of each phosphorus pollution source.

[0053] In another embodiment of the present invention, a computer-readable storage medium is also provided, which stores a computer program that, when executed by a processor, implements the steps of any of the above-described methods for analyzing phosphorus pollution sources in water bodies.

[0054] In another embodiment of the present invention, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to perform the steps of any of the water phosphorus pollution source analysis methods described in the above embodiments.

[0055] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated.

[0056] The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can access, or a data storage device such as a server or data center that integrates one or more available media. The available medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., a solid-state drive (SSD)).

[0057] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0058] In addition, the functional modules in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0059] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for source apportionment of phosphorus pollution in water bodies based on combined tracing of conservative tracer ions and oxygen isotopes, characterized in that, The method includes: In response to a request for phosphorus pollution source tracing in a target water area, a preset phosphorus source isotope fingerprint spectrum is obtained, and the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected at each section of the target water area are determined; the conservative tracer ions include at least one of chloride ions and bromide ions. Based on the conservative tracer ion concentration and phosphate oxygen isotope composition, a conservative ion-isotope joint tracer model is constructed to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area. The joint tracer model uses endmember mixing analysis of conservative tracer ions to determine the water contribution ratio of each potential pollution source, and then uses the water contribution ratio to constrain the isotope mixing model based on the isotope fingerprint to quantitatively analyze the phosphorus load contribution rate of each potential pollution source.

2. The method for source apportionment of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 1, characterized in that, The data collection sections include river sections flowing into the lake, lake sections, and groundwater monitoring well sections. The cross-sections of the rivers flowing into the lake are set upstream of the entrances of each river into the target water area, and three sampling depths—surface, middle and bottom—are set on the same cross-section. The cross-sections within the lake are set up using a grid-based sampling method based on the shape and size of the target water area. In areas with stratification, at least one sampling point is set up in each of the surface, thermocline, and bottom layers. The groundwater monitoring well sections are arranged along the shoreline of the target water area.

3. The water phosphorus pollution source apportionment method based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 1, characterized in that, The phosphorus-derived isotope fingerprint was established through the following steps: Representative end-member samples of each potential phosphorus pollution source are obtained. The end-member samples are samples that can characterize the isotopic features of the pollution source. The potential phosphorus pollution sources include at least two of the following: agricultural non-point sources, domestic sewage sources, industrial wastewater sources, and lake sediment release sources. The phosphate oxygen isotope characteristic values ​​of each end-member sample were determined; based on the end-member samples and their corresponding isotope characteristic values, the isotope fingerprint spectrum was constructed.

4. The method for source apportionment of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 1, characterized in that, The determination of the conserved tracer ion concentration and phosphate oxygen isotope composition in water samples collected from each section of the target water area includes: The concentration of the conservative tracer ions was determined by ion chromatography or electrochemical detection. The conservative tracer ions are those whose concentration changes in water are dominated by physical dilution and mixing. Phosphate in the water sample was extracted into silver phosphate solid using silver salt precipitation. The silver phosphate solid was then thermally decomposed into carbon monoxide gas. The carbon monoxide gas was analyzed by delta-isotope ratio mass spectrometry. 18 The oxygen isotope composition of the phosphate was obtained by measuring the O value.

5. The method for source apportionment of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 1, characterized in that, The construction of the conservative ion-isotope joint tracing model includes: Based on the aforementioned conservative tracer ion concentration, let the conservative ion concentration vector of each potential pollution source be... The conservative ion concentration vector of the mixed water body is By solving the mixed constraint equations = ,and , Determine the water volume contribution ratio of each potential pollution source. ; Based on the phosphate oxygen isotope composition and the j-th pollution source end-member in the isotope fingerprint spectrum Eigenvalues By using a Bayesian mixture model and employing the Markov chain Monte Carlo method for parameter estimation, the mixture equations are solved. Calculate the phosphorus load contribution rate of each potential pollution source. ,in For the actual measurement of mixed samples value, This is the model error term; Based on the aforementioned water contribution ratio Contribution rate of the phosphorus load Joint constraint optimization was performed to obtain the corrected phosphorus load contribution rate of each potential pollution source.

6. The water phosphorus pollution source apportionment method based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 5, characterized in that, The water volume contribution ratio Contribution rate of the phosphorus load Joint constraint optimization was performed to obtain the corrected phosphorus load contribution rates of each potential pollution source, including: The water volume contribution ratio The phosphorus contribution of water volume is obtained by weighting the phosphorus concentration of the corresponding pollution source. The water-weighted phosphorus contribution reference value is compared with the phosphorus load contribution rate output by the Bayesian mixture model. Perform a comparison; When the deviation between the two exceeds a preset threshold, the input data of the Bayesian mixture model is verified and corrected, and the corrected phosphorus load contribution rate is recalculated.

7. The method for source apportionment of phosphorus pollution in water bodies based on the combined tracing of conservative tracer ions and oxygen isotopes according to claim 1, characterized in that, The method further includes: generating a phosphorus pollution source composition map of the target water area based on the contribution rate of each potential phosphorus pollution source obtained by analysis. The source composition map includes at least one of the following: a pie chart of pollution source contribution rate, a phosphorus contribution heat map of the river section flowing into the lake, and a spatiotemporal variation trend map of phosphorus load.

8. A water phosphorus pollution source apportionment system based on the combined tracing of conservative tracer ions and oxygen isotopes, used to implement the water phosphorus pollution source apportionment method as described in any one of claims 1-7, characterized in that, include: The data acquisition module is used to acquire a preset phosphorus-derived isotope fingerprint spectrum and to determine the concentration of conservative tracer ions and the phosphate oxygen isotope composition in water samples collected from each section of the target water area. The model building module is used to construct a conservative ion-isotope joint tracer model based on the conservative tracer ion concentration and phosphate oxygen isotope composition. The source analysis module is used to analyze the contribution rate of each potential phosphorus pollution source to the phosphorus load in the target water area through the joint tracer model. The model building module includes: The end-member mixing analysis unit is used to determine the water volume contribution ratio of each potential pollution source based on the conservative tracer ion concentration. An isotope mixing analysis unit is used to calculate the phosphorus load contribution rate of each potential pollution source based on the phosphate oxygen isotope composition and the isotope fingerprint spectrum. A joint constraint unit is used to constrain and optimize the phosphorus load contribution rate based on the water volume contribution ratio.

9. The water phosphorus pollution source apportionment system according to claim 8, characterized in that, The data acquisition module includes a conservative ion detection unit, which includes an ion chromatography analysis subunit and a data processing subunit. The ion chromatography analysis subunit is used to detect the concentrations of chloride and bromide ions, and the data processing subunit is used to calculate the concentration values ​​of each ion based on the peak area of ​​the ion chromatography and generate a sampling point-ion concentration comparison table. The data acquisition module includes an isotope analysis unit, which comprises a phosphate extraction subunit, a high-temperature thermal conversion subunit, and an isotope ratio mass spectrometry subunit. The phosphate extraction subunit extracts phosphate from the water sample into silver phosphate solid using silver salt precipitation. The high-temperature thermal conversion subunit thermally decomposes the silver phosphate solid into carbon monoxide gas at 1450°C. The isotope ratio mass spectrometry subunit analyzes the δ¹⁸O values ​​of the carbon monoxide gas. 18 The O value was measured.

10. The water phosphorus pollution source apportionment system according to claim 8, characterized in that, It also includes a sampling deployment module for obtaining the sampling section setting information of the target water area and its surrounding catchment area; the sampling sections include the river sections flowing into the lake, the lake body sections, and the groundwater monitoring well sections.

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