An isotopic and biological tracer combined tracing method and system for nitrogen pollution in a water body

Abstract

The application discloses a kind of water body nitrogen pollution isotope and biological tracer combined tracing method and system, the method includes the type and position of irrigation and drainage ditch of irrigation area to be researched to determine different pollution source area;Surface water sample and groundwater sample are collected in irrigation and drainage ditch, the sample is analyzed, the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance and coprostanol concentration are determined;Based on sample analysis result, the contribution ratio of point source pollution source and non-point source pollution source of surface water and its load are determined;The contribution of groundwater non-point source pollution source and its load are determined.The present application comprehensively collects surface water and groundwater, and uses multi-technology nesting method to analyze the pollution source contribution and load of surface water and groundwater.By distinguishing point source and non-point source, and using nitrogen and oxygen double isotope technology to identify non-point source pollution, combined with biological marker coprostanol to distinguish livestock manure and domestic sewage, the specific contribution and load of each pollution source are effectively quantified.

Description

Technical Field

[0001] This invention relates to the field of agricultural non-point source pollution tracing technology, and in particular to a method and system for tracing nitrogen pollution in water bodies using a combination of isotopes and biological tracers. Background Technology

[0002] In arid and semi-arid irrigation areas, especially in the upper reaches of the Yellow River, the region possesses unique hydrological complexity characterized by the interconnection of multi-level irrigation and drainage ditches with shallowly buried groundwater. Driven by the extensive water and fertilizer management model of flood irrigation, the sources of nitrogen pollution are unclear, and the contribution of non-point source pollution is unknown, leading to increasingly prominent agricultural non-point source pollution problems. While various pollution source tracing methods exist in existing technologies, these methods have many shortcomings when applied to the upper reaches of the Yellow River irrigation area.

[0003] For example, the fluorescence characteristic method of dissolved organic matter can calculate the contribution rate of point source and non-point source pollution using the fluorescence characteristics of dissolved organic matter, but it can only obtain the overall contribution rate of point source and non-point source pollution, and cannot break down the contribution rate of each non-point source pollution source. Furthermore, it does not involve tracing the source of nitrogen pollutants in groundwater, and cannot be applied to irrigation areas where irrigation water infiltrates.

[0004] Although the combined technology source tracing method (such as the nitrate nitrogen and oxygen isotope combined SWAT model) uses multiple technologies for source tracing, it is mainly aimed at the rainy season and dry season. It does not apply nitrate nitrogen and oxygen isotope source tracing to the characteristics of the Yellow River irrigation system and does not involve groundwater sampling, thus limiting its application scenarios. At the same time, it cannot distinguish between livestock and poultry manure pollution sources and domestic sewage pollution sources, nor can it identify point source pollution.

[0005] Existing isotope and modeling methods focus on a single medium (surface water or groundwater). They use two-dimensional water quality models to calculate the contribution of point sources and the proportion of non-point sources to downstream pollution by combining the concentration of pollutants emitted from point sources with the mass concentration of pollutants measured at water quality monitoring points. However, these methods rely on field monitoring data, which makes it difficult to obtain data parameters, is costly, and results in high uncertainty. Furthermore, they cannot distinguish between livestock and poultry manure pollution sources and domestic sewage pollution sources, and they do not involve tracing the source of groundwater nitrogen pollution or quantifying the pollution source load.

[0006] In summary, existing technologies cannot effectively trace the source of nitrogen pollutants in groundwater in arid and semi-arid irrigation areas, cannot subdivide the contribution rate of each non-point source pollution source, cannot accurately distinguish between livestock and poultry manure and domestic sewage pollution sources, have limited application scenarios, are difficult and costly to acquire data, and cannot identify point source pollution. Summary of the Invention

[0007] This invention provides a method and system for tracing the source of nitrogen pollution in water bodies using isotopes and biological tracers, aiming to solve the technical problems of unclear baseline data and unknown sources of agricultural non-point source pollution in the irrigation area of ​​the upper Yellow River, so as to achieve accurate identification and quantitative analysis of nitrogen pollution sources in surface water and groundwater in the irrigation area.

[0008] A combined isotope and biological tracer method for tracing the source of nitrogen pollution in water bodies includes:

[0009] S1. Investigate the types and locations of irrigation and drainage ditches in the irrigation area to be studied in order to identify different pollution source areas;

[0010] S2. Collect surface water and groundwater nitrate samples from irrigation and drainage ditches, analyze the samples, and determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance, and fecal sterol concentration.

[0011] S3. Based on the sample analysis results, determine the contribution ratio of point source pollution sources and non-point source pollution sources to surface water and the surface water pollution load;

[0012] Step S3 further includes the following sub-steps:

[0013] S301. Using three-dimensional fluorescence fingerprinting technology, point source pollution sources in nitrogen pollutants collected from irrigation and drainage ditches are identified, and the contribution ratio of point sources and area sources is calculated using an end-member mixing model.

[0014] S302. Using nitrate nitrogen and oxygen dual isotope tracers combined with a Bayesian mixture model, the contribution of non-point source pollution from different nitrogen pollution sources in surface water is accurately and quantitatively analyzed.

[0015] S303. Using the biomarker fecal sterol, the contributions of livestock and poultry manure pollution and domestic water pollution in fecal wastewater sources are distinguished, and the contribution ratio is calculated using a second endmember mixture model. The expression for the second endmember mixture model is:

[0016] in, This indicates the concentration of fecal sterols in the water sample. This indicates the concentration of fecal sterols in the endmembers of livestock and poultry manure pollution sources. This indicates the concentration of fecal sterols in the endmembers of domestic sewage pollution sources; This indicates the percentage contribution of livestock and poultry manure to pollution. This indicates the percentage of pollution caused by domestic sewage.

[0017] The contribution of livestock and poultry manure to pollution in exported water samples The contribution of domestic sewage pollution The model was validated using the coefficient of determination R² and residual analysis; the actual proportions of livestock and poultry manure pollution sources and domestic sewage pollution sources were obtained by multiplying them by the contribution ratio of livestock and poultry manure.

[0018] S304. Based on the contribution ratio of point source pollution sources and non-point source pollution sources of surface water, the flux of monitoring points in irrigation and drainage ditches and the weighted concentration of nitrogen pollutants emitted at monitoring sections, calculate the load of each pollution source in surface water.

[0019] S4. Based on the sample analysis results, determine the contribution of groundwater non-point source pollution and the groundwater pollution load; step S4 also includes the following sub-steps:

[0020] S401. Using nitrate nitrogen and oxygen dual isotope tracing combined with Bayesian mixture model to quantitatively analyze different sources of nitrogen pollution in groundwater in irrigation area, and using the biomarker coprostadanol to distinguish the contribution ratio of livestock and poultry manure and domestic sewage in fecal sewage pollution sources.

[0021] S402. The process of surface water infiltration into groundwater is simulated using the Hydrus-2D model to quantify the groundwater flux; the governing equation of the Hydrus-2D model is expressed as follows:

[0022] (9)

[0023] in, Indicates soil moisture content, Indicates time, and Represents spatial coordinates, Indicates soil hydraulic conductivity. Indicates soil pressure head. Indicates the root system's water absorption rate;

[0024] S403. The van Genuchten-Mualem model is used to characterize the soil moisture characteristic curve and its hydraulic conductivity. The expression of the van Genuchten-Mualem model is as follows:

[0025] (10)

[0026] (11)

[0027] (12)

[0028] in, Indicates saturated hydraulic conductivity. Indicates effective saturation. Indicates the soil saturation moisture content. This indicates the residual soil moisture content. Represents the porosity correlation coefficient, which is superscript, 0.5; , , Represents empirical parameters of the model shape;

[0029] S404. Based on the actual contribution ratio of each non-point source pollution source to groundwater, the groundwater flux quantified by the Hydrus-2D model, and the weighted concentration of nitrogen pollutant emissions, the load of each pollution source to groundwater is calculated.

[0030] A combined isotope and biological tracer source tracing system for nitrogen pollution in water bodies includes:

[0031] The irrigation and drainage system survey module is used to survey the types and locations of irrigation and drainage ditches in the irrigation area to be studied, in order to identify different pollution source areas.

[0032] The sample collection and analysis module is used to collect surface water and groundwater samples from irrigation and drainage ditches, analyze the samples, and determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance, and coprostinol concentration.

[0033] The surface water pollution source contribution analysis module is used to determine the contribution ratio of point source pollution sources and non-point source pollution sources, as well as the surface water pollution load, based on sample analysis results.

[0034] The groundwater pollution source contribution analysis module is used to determine the contribution of groundwater non-point source pollution and groundwater pollution load based on sample analysis results.

[0035] This invention proposes a comprehensive method and system for tracing nitrogen pollution sources in arid and semi-arid irrigation areas, specifically addressing the unique hydrological complexity of the upper Yellow River irrigation district. This method effectively distinguishes and quantifies the contributions of point and non-point source pollution, as well as the specific contribution ratio and output load of each non-point source pollution source, through the combined application of multiple technologies. Three-dimensional fluorescence fingerprinting technology is used to identify point source pollution sources in surface water and clarify the total contribution ratio of point and non-point source pollution. Simultaneously, by combining nitrate and nitrogen-oxygen dual-isotope tracing with a Bayesian mixture model, the contributions of non-point source pollution from different sources such as agricultural fertilizers, soil organic nitrogen, and fecal sewage in surface water and groundwater are further precisely quantified. Fecal sterol is used as a biomarker to further refine the contribution ratio of livestock and poultry manure and domestic sewage in fecal sewage pollution sources. By combining surface water monitoring flux and groundwater flux quantified by the Hydrus-2D model, as well as the weighted concentration of nitrogen pollutant emissions, the load of each pollution source can be calculated, ultimately clarifying the contribution and load variation patterns of various pollution sources in surface water and groundwater in the irrigation district.

[0036] This invention uses the biomarker fecal sterol to distinguish the contributions of livestock and poultry manure and domestic sewage. This innovation overcomes the limitation of existing technologies that cannot distinguish the specific contribution ratios of livestock and poultry manure and domestic sewage in manure and sewage pollution sources. This method enables a more accurate quantification of the contribution ratios of various non-point source pollution sources in surface water and groundwater, providing more precise data support for the management and control of agricultural non-point source pollution.

[0037] Furthermore, the method of this invention belongs to a multi-level nested source tracing approach, significantly improving the accuracy of identifying nitrogen pollution sources in arid and semi-arid irrigation areas. Specifically, by integrating multiple technical means, it first distinguishes between point and non-point sources of surface water pollution. Then, it uses nitrogen and oxygen dual-isotope technology to further subdivide these non-point source pollutants, clarifying the specific contributions of different pollution sources such as agricultural fertilizers, soil organic nitrogen, and sewage. Furthermore, by introducing the biomarker coprosterol, it meticulously distinguishes the contributions of livestock and poultry manure and domestic sewage in sewage, thereby achieving multi-level refinement of pollution sources. For groundwater, the same nitrogen and oxygen dual-isotope technology and biomarker methods are applied, combined with the Hydrus-2D model to quantitatively calculate the groundwater flux, accurately calculating the load of each pollution source. This multi-level nested approach not only improves the accuracy of source tracing but also provides a more scientific and systematic solution for the management and control of nitrogen pollution in irrigation areas. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of a method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers, according to an embodiment of the present invention.

[0040] Figure 2 This is a structural diagram of a combined isotope and biological tracer source tracing system for nitrogen pollution in water bodies, according to an embodiment of the present invention. Detailed Implementation

[0041] 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, not all, of the embodiments of the present invention. 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.

[0042] The present invention provides a method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers. This method can be applied to a system for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers.

[0043] In one embodiment, such as Figure 1 As shown, a combined isotope and biological tracer method for tracing the source of nitrogen pollution in water bodies is provided, comprising the following steps:

[0044] S1. Investigate the types and locations of irrigation and drainage ditches in the irrigation area to be studied in order to identify different pollution source areas.

[0045] In one embodiment, step S1 further includes the following sub-steps:

[0046] S101. Before tracing the source, identify the types of irrigation and drainage ditches in the irrigation area to be studied, divide the irrigation and drainage ditches into irrigation canals, drainage canals and drainage ditches, and identify the location distribution of the main ditches and branch ditches.

[0047] S102. Based on the distribution characteristics of planting irrigation, aquaculture drainage, rural life, and industrial areas in the irrigation district to be studied, determine the regions of different pollution sources.

[0048] S2. Collect surface water and groundwater samples from irrigation and drainage ditches, analyze the samples, and determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance, and fecal sterol concentration, and collect water pollutants.

[0049] In one embodiment, step S2 further includes the following sub-steps:

[0050] S201. Collect surface water samples from irrigation and drainage ditches and groundwater samples from wells in the irrigation area to be studied. The sampling period is divided according to the irrigation period: May for spring irrigation, June-September for summer irrigation, and October-November for autumn irrigation. Sampling is carried out after each irrigation period. During each sampling period, a water sampler is used to collect 500-600ml of sample at each sampling point.

[0051] S202. The fluorescence peak intensity of surface water samples was measured.

[0052] S203. Surface water and groundwater samples were subjected to δ¹⁸O⁻ analysis. 15 N-NO3 - Laboratory analysis was conducted to determine the nitrogen isotope abundance of nitrate in the water sample.

[0053] S204. Surface water and groundwater samples were subjected to δ¹⁸O⁻ analysis. 18 O-NO3 - Laboratory analysis was conducted to determine the oxygen isotope abundance of nitrate in the water sample.

[0054] S205. Measure the concentration of coprostinol in surface water and groundwater samples, and based on the coprostinol concentration data, distinguish the contributions of livestock and poultry manure and domestic sewage.

[0055] S3. Based on the sample analysis results, determine the contribution ratio of point source pollution sources and non-point source pollution sources to surface water, as well as the surface water pollution load.

[0056] In one embodiment, step S3 further includes the following sub-steps:

[0057] S301. Using three-dimensional fluorescence fingerprinting technology, point source pollution sources in nitrogen pollutants collected from irrigation and drainage ditches are identified, and the contribution ratio of point sources and area sources is calculated using an end-member mixing model. Specifically, the three-dimensional fluorescence fingerprint (Excitation-Emission Matrix Fluorescence Spectroscopy, EEM) is a visual fingerprint formed by collecting three-dimensional data of "excitation wavelength (Ex) - emission wavelength (Em) - fluorescence intensity (I)" using a fluorescence spectrophotometer, reflecting the types and relative contents of fluorescent components (such as humic acid, proteins, aromatic compounds, etc.) in the water sample.

[0058] In one embodiment, step S301 further includes the following sub-steps:

[0059] S3011. Using three-dimensional fluorescence fingerprinting technology, three-dimensional data of excitation wavelength, emission wavelength, and fluorescence intensity of water samples are collected by a fluorescence spectrophotometer to form a visual fingerprint; the peak extraction method is used to read the fluorescence peaks (excitation wavelength / emission wavelength) in the fluorescence fingerprint spectrum of the water sample, and the fluorescence peaks are compared with the fluorescence peaks of known fluorescent substances. When the spectrum similarity exceeds 90%, it is qualitatively determined to be the source of pollution, thereby identifying point source pollution;

[0060] S3012. Calculate the contribution ratio of point sources and the contribution ratio of area sources using the first end-member mixing model. The expression for the first end-member mixing model is:

[0061] =1(1)

[0062] + (2)

[0063] in, Indicates the intensity of the fluorescence peak in the water sample. Indicates the intensity of the fluorescence peak in the point source endmember. Indicates the intensity of the fluorescence peak in the surface source endmember; Indicates the percentage of contribution from point sources. This represents the proportion of surface source contribution. Equations (1)-(2) are established based on the linear mixing assumption.

[0064] S302, using nitrate nitrogen-oxygen dual isotopes (δ¹⁰) 15 N-NO3 - This study uses tracer analysis combined with a Bayesian mixture model to accurately and quantitatively analyze the non-point source pollution contribution ratio of different nitrogen pollution sources in surface water (such as agricultural fertilizers, soil organic nitrogen, and sewage). It outputs the point source contribution ratio for each target water sample. and the proportion of surface source The model was statistically analyzed for patterns in different time and space, and the reliability of the model was verified using the coefficient of determination (R²) and residual analysis.

[0065] In one embodiment, step S302 further includes the following sub-steps:

[0066] S3021. The contribution rate of nitrate pollution sources in water samples is quantified based on the Bayesian mixture model MixSIAR in R language (v4.3.1). The expression of the Bayesian mixture model is as follows:

[0067] = ( + )+ (3)

[0068] ~N( (4)

[0069] ~N( (5)

[0070] ~N( (6)

[0071] in, Indicates the isotopes in mixture sample i The value, N; J; Indicates source Contribution rate, K; Calculated using the MixSIAR model; Indicates source medium isotope The value, Follows a normal distribution N( ), This represents the average value. Indicates standard deviation; Indicates source medium isotope The value, Follows a normal distribution N( ), This represents the average value. Indicates standard deviation; Residuals represent the undetermined variables between different water samples. Follows a normal distribution N( ), This represents the average value. It represents the standard deviation.

[0072] S3022. The contribution percentage of pollution sources outputting agricultural fertilizers, soil organic nitrogen, and fecal sewage is multiplied by the total non-point source pollution percentage identified using three-dimensional fluorescence spectroscopy to obtain the actual contribution percentage of each non-point source pollution from different nitrogen pollution sources in surface water.

[0073] S303. Using the biomarker fecal sterol, the contributions of livestock and poultry manure pollution and domestic water pollution in fecal wastewater sources are distinguished, and the contribution ratio is calculated using a second endmember mixture model. The expression for the second endmember mixture model is:

[0074] =1(7)

[0075] + (8)

[0076] in, This indicates the concentration of fecal sterols in the water sample. This indicates the concentration of fecal sterols in the endmembers of livestock and poultry manure pollution sources. This indicates the concentration of fecal sterols in the endmembers of domestic sewage pollution sources; This indicates the percentage contribution of livestock and poultry manure to pollution. This indicates the percentage of pollution caused by domestic sewage.

[0077] Understandably, current nitrogen and oxygen isotope methods used for tracing agricultural non-point source nitrogen pollution cannot separate the contributions of livestock and poultry manure and domestic sewage pollution in fecal wastewater sources. This invention overcomes this technical bottleneck by utilizing the biomarker coprosterol to differentiate between livestock and poultry manure and domestic sewage in fecal wastewater sources. Livestock and poultry manure pollution in fecal wastewater sources mainly originates from herbivorous animal manure, while domestic sewage pollution mainly originates from human feces. Coprosterol is a lipid compound produced in the animal intestines. Herbivorous animal coprosterol contains a lower proportion of coprosterol, while human feces contain a higher proportion. Coprosterol is structurally stable and highly conserved.

[0078] The contribution of livestock and poultry manure to pollution in exported water samples The contribution of domestic sewage pollution The model was validated using the coefficient of determination R² and residual analysis. Multiplying these values ​​by the contribution percentage of livestock and poultry manure, the actual proportions of livestock and poultry manure pollution sources and domestic sewage pollution sources were obtained.

[0079] S304. Based on the contribution ratio of point source pollution sources and non-point source pollution sources to surface water, the flux of monitoring points in irrigation and drainage ditches, and the weighted concentration of nitrogen pollutants emitted at monitoring sections, calculate the load of each pollution source in surface water.

[0080] S4. Based on the sample analysis results, determine the contribution of groundwater non-point source pollution sources and the groundwater pollution load.

[0081] In one embodiment, step S4 further includes the following sub-steps:

[0082] S401. Using nitrate-nitrogen-oxygen dual isotope tracing combined with a Bayesian mixture model, the different sources of nitrogen pollution in the irrigation area's groundwater (agricultural fertilizers, soil organic nitrogen, and sewage) are quantitatively analyzed. The biomarker coprosterol is used to differentiate the contribution proportions of livestock and poultry manure and domestic sewage in the sewage pollution source. The principle of this step is similar to steps S3021 and S303, and will not be elaborated further.

[0083] S402. The process of surface water infiltration into groundwater is simulated using the Hydrus-2D model to quantify the groundwater flux; the governing equation of the Hydrus-2D model is expressed as follows:

[0084] (9)

[0085] in, Indicates soil moisture content, Indicates time, and Represents spatial coordinates, Indicates soil hydraulic conductivity. Indicates soil pressure head. This represents the root water absorption rate. The governing equations of the Hydrus-2D model are two-dimensional saturated / unsaturated soil water movement equations, namely the Richard equations, which are constructed based on Darcy's law and the mass conservation equation.

[0086] S403. The van Genuchten-Mualem model is used to characterize the soil moisture characteristic curve and its hydraulic conductivity. The expression of the van Genuchten-Mualem model is as follows:

[0087] (10)

[0088] (11)

[0089] (12)

[0090] in, Indicates saturated hydraulic conductivity. Indicates effective saturation. Indicates the soil saturation moisture content. This indicates the residual soil moisture content. Represents the porosity correlation coefficient, which is superscript, 0.5; , , Represents empirical parameters for the shape of the model.

[0091] S404. Based on the actual contribution ratio of each non-point source pollution source to groundwater, the groundwater flux quantified by the Hydrus-2D model, and the weighted concentration of nitrogen pollutant emissions, the load of each pollution source to groundwater is calculated.

[0092] In one specific embodiment, the model region setting and boundary conditions are as follows: Considering the widespread use of plastic film mulching in the arid irrigation areas of Northwest China, a typical crop such as corn with one film and two rows is used as a representative unit of cultivated land, with a cross-section of 120cm wide and 300cm deep as the simulation object. The middle 70cm of the upper boundary is covered by plastic film, while the left and right 25cm are uncovered. The simulation region is divided into triangular units, with a minimum spacing of 1cm and a maximum spacing of 5cm between nodes. The initial condition is the observed soil profile moisture content. The Hydrus-2D model can freely set the boundaries of the simulation region. During the simulation, the area of ​​the upper boundary not covered by plastic film is set as the atmospheric boundary, and the area covered by plastic film is set as the zero flux boundary; the lower boundary is set as the variable head boundary according to the groundwater level changes; both left and right boundaries are set as zero flux boundaries (water-resistant boundaries).

[0093] Meteorological data and crop evapotranspiration calculation: Based on temperature, radiation, wind speed, humidity, and other data monitored by meteorological stations, the Penman-Monteith formula recommended in FAO-56 was used to calculate the daily reference crop evapotranspiration (ET0). The dual crop coefficient method was used to divide the crop evapotranspiration ET0 into plant potential transpiration (T). p ) and soil potential evaporation (E p These data points serve as inputs for root water uptake and upper boundary evaporation, respectively. Observed rainfall and irrigation data are used as inputs for the upper boundary inflow.

[0094] Soil parameters and model type selection: The soil parameters required for Hydrus-2D numerical simulation include saturated hydraulic conductivity K. s Soil pore connectivity coefficient The reciprocal of soil air intake value Soil saturated moisture content Soil residual moisture content The Rosetta Lite v.1.1 software in the Hydrus-2D model was used to estimate soil parameters by inputting the content of sand, silt, and clay particles, as well as soil bulk density and field water holding capacity. The model type was selected as 2D-General, and the X and Z planes were selected to build the model. The Water Flow module in the model was applied.

[0095] Model Simulation Period and Output: The simulation period is the entire year, totaling 365 days. The time scale is daily, with an initial time of 0 and an ending time of 365. The initial time step, maximum, and minimum time steps are the model's default values. Simulation results are output daily. The VGM flow model is selected, and parameters are set. Finite element generation, simulation region mapping, initial condition setting, and boundary condition setting are then performed. Finally, the simulation is run, and the results are calculated. The simulation results directly provide the daily changes in groundwater flux at the groundwater surface, thus obtaining the groundwater recharge flux. The final output is the groundwater flux.

[0096] Pollution source load calculation: By combining the actual contribution ratio of each non-point source pollution source to groundwater, the groundwater flux quantified by the Hydrus-2D model, and the weighted concentration of nitrogen pollutants emitted, the load of each pollution source in groundwater is calculated. This method allows for the assessment of load changes of various pollution sources in groundwater, providing a scientific basis for pollution control and water resource management.

[0097] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0098] In one embodiment, a combined isotope and biological tracer tracing system for nitrogen pollution in water bodies is provided, which corresponds one-to-one with the method of the combined isotope and biological tracer tracing system for nitrogen pollution in water bodies described in the above embodiments. For example... Figure 2 As shown, the combined isotope and biological tracer source tracing system for nitrogen pollution in this water body includes:

[0099] The irrigation and drainage system survey module 100 is used to survey the types and locations of irrigation and drainage ditches in the irrigation area to be studied, so as to identify different pollution source areas.

[0100] The sample collection and analysis module 200 is used to collect surface water and groundwater samples from irrigation and drainage ditches, analyze the samples, and determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance, and fecal sterol concentration.

[0101] The surface water pollution source contribution analysis module 300 is used to determine the contribution ratio of point source pollution sources and non-point source pollution sources, as well as the surface water pollution load, based on sample analysis results.

[0102] The Groundwater Pollution Source Contribution Analysis Module 400 is used to determine the contribution of groundwater non-point source pollution sources and groundwater pollution load based on sample analysis results.

[0103] Specific limitations regarding the combined isotope and biological tracer source tracing system for nitrogen pollution in water bodies can be found in the limitations of the combined isotope and biological tracer source tracing method for nitrogen pollution in water bodies mentioned above, and will not be repeated here. Each module in the aforementioned combined isotope and biological tracer source tracing system for nitrogen pollution in water bodies can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0104] In one embodiment, a computer device is provided, which may be a server. The computer device includes a processor, memory, a network interface, and a database connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The network interface is used to communicate with external terminals via a network connection. When the computer program is executed by the processor, it implements a method for joint tracing of nitrogen pollution in water bodies using isotopes and biological tracers.

[0105] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above.

[0106] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers, characterized in that, include: S1. Investigate the types and locations of irrigation and drainage ditches in the irrigation area to be studied in order to identify different pollution source areas; S2. Collect surface water and groundwater samples from irrigation and drainage ditches, analyze the samples, and determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance, and fecal sterol concentration. S3. Based on the sample analysis results, determine the contribution ratio of point source pollution sources and non-point source pollution sources to surface water and the surface water pollution load; Step S3 further includes the following sub-steps: S301. Using three-dimensional fluorescence fingerprinting technology, point source pollution sources in nitrogen pollutants collected from irrigation and drainage ditches are identified, and the contribution ratio of point sources and area sources is calculated using an end-member mixing model. S302. Using nitrate nitrogen and oxygen dual isotope tracers combined with a Bayesian mixture model, the contribution of non-point source pollution from different nitrogen pollution sources in surface water is accurately and quantitatively analyzed. S303. Using the biomarker fecal sterol, the contributions of livestock and poultry manure pollution and domestic water pollution in fecal wastewater sources are distinguished, and the contribution ratio is calculated using a second endmember mixture model. The expression for the second endmember mixture model is: =1(7) + (8) in, This indicates the concentration of fecal sterols in the water sample. This indicates the concentration of fecal sterols in the endmembers of livestock and poultry manure pollution sources. This indicates the concentration of fecal sterols in the endmembers of domestic sewage pollution sources; This indicates the percentage contribution of livestock and poultry manure pollution. This indicates the percentage of pollution caused by domestic sewage. The contribution of livestock and poultry manure to pollution in exported water samples The contribution of domestic sewage pollution The model was validated using the coefficient of determination R² and residual analysis; the actual proportions of livestock and poultry manure pollution sources and domestic sewage pollution sources were obtained by multiplying them by the contribution ratio of livestock and poultry manure. S304. Based on the contribution ratio of point source pollution sources and non-point source pollution sources of surface water, the flux of monitoring points in irrigation and drainage ditches and the weighted concentration of nitrogen pollutants emitted at monitoring sections, calculate the load of each pollution source in surface water. S4. Based on the sample analysis results, determine the contribution of groundwater non-point source pollution sources and the groundwater pollution load; Step S4 further includes the following sub-steps: S401. Using nitrate nitrogen and oxygen dual isotope tracing combined with Bayesian mixture model to quantitatively analyze different sources of nitrogen pollution in groundwater in irrigation area, and using the biomarker coprostadanol to distinguish the contribution ratio of livestock and poultry manure and domestic sewage in fecal sewage pollution sources. S402. The process of surface water infiltration into groundwater is simulated using the Hydrus-2D model to quantify the groundwater flux; the governing equation of the Hydrus-2D model is expressed as follows: （9） in, Indicates soil moisture content, Indicates time, and Represents spatial coordinates, Indicates soil hydraulic conductivity. Indicates soil pressure head. Indicates the root system's water absorption rate; S403. The van Genuchten-Mualem model is used to characterize the soil moisture characteristic curve and its hydraulic conductivity. The expression of the van Genuchten-Mualem model is as follows: （10） （11） （12） in, Indicates saturated hydraulic conductivity. Indicates effective saturation. Indicates the soil saturation moisture content. This indicates the residual soil moisture content. Represents the porosity correlation coefficient, which is superscript, 0.5; , , Represents empirical parameters of the model shape; S404. Based on the actual contribution ratio of each non-point source pollution source to groundwater, the groundwater flux quantified by the Hydrus-2D model, and the weighted concentration of nitrogen pollutant emissions, the load of each pollution source to groundwater is calculated.

2. The method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers according to claim 1, characterized in that, Step S1 further includes the following sub-steps: S101. Determine the types of irrigation and drainage ditches in the irrigation area to be studied, divide the irrigation and drainage ditches into irrigation canals, drainage canals and drainage ditches, and determine the location and distribution of the main ditches and branch ditches. S102. Based on the distribution characteristics of planting irrigation, aquaculture drainage, rural life, and industrial areas in the irrigation district to be studied, determine the regions of different pollution sources.

3. The method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers according to claim 2, characterized in that, Step S2 further includes the following sub-steps: S201. Collect surface water samples from irrigation and drainage ditches and groundwater samples from wells in the irrigation area to be studied. The sampling period is divided according to the irrigation period: May for spring irrigation, June-September for summer irrigation, and October-November for autumn irrigation. Sampling is carried out after each irrigation period. During each sampling period, a water sampler is used to collect 500-600ml of sample at each sampling point. S202. Determine the fluorescence peak intensity of surface water samples; S203. Surface water and groundwater samples were subjected to δ¹⁸O⁻ analysis. 15 N-NO3 - Laboratory analysis was conducted to determine the nitrogen isotope abundance of nitrate in the water sample; S204. Surface water and groundwater samples were subjected to δ¹⁸O⁻ analysis. 18 O-NO3 - Laboratory analysis was conducted to determine the oxygen isotope abundance of nitrate in the water sample. S205. Measure the concentration of coprostinol in surface water and groundwater samples, and based on the coprostinol concentration data, distinguish the contributions of livestock and poultry manure and domestic sewage.

4. The method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers according to claim 3, characterized in that, Step S301 further includes the following sub-steps: S3011. Using three-dimensional fluorescence fingerprinting technology, three-dimensional data of the excitation wavelength, emission wavelength and fluorescence intensity of water samples are collected by a fluorescence spectrophotometer to form a visual fingerprint; The peak-stripping method is used to read the fluorescence peaks in the fluorescence fingerprint spectrum of water samples. The fluorescence peaks are compared with the fluorescence peaks of known fluorescent substances. When the similarity of the spectra exceeds 90%, it is qualitatively determined to be the source of pollution, thereby identifying point source pollution. S3012. Calculate the contribution ratio of point sources and the contribution ratio of area sources using the first end-member mixing model. The expression for the first end-member mixing model is: =1(1) + (2) in, Indicates the intensity of the fluorescence peak in the water sample. Indicates the intensity of the fluorescence peak in the point source endmember. Indicates the intensity of the fluorescence peak in the surface source endmember; Indicates the percentage of contribution from point sources. This indicates the percentage of contribution from surface sources.

5. The method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers according to claim 4, characterized in that, Step S302 further includes the following sub-steps: S3021. The contribution rate of nitrate pollution sources in water samples is quantified based on the Bayesian mixture model in R language. The expression of the Bayesian mixture model is: = ( + )+ （3） ~N( )（4） ~N( )（5） ~N( )（6） in, Indicates the isotopes in mixture sample i The value, N; J; Indicates source Contribution rate, K; Calculated using the MixSIAR model; Indicates source medium isotope The value, Follows a normal distribution N( ), This represents the average value. Indicates standard deviation; Indicates source medium isotope The value, Follows a normal distribution N( ), This represents the average value. Indicates standard deviation; Residuals represent the undetermined variables between different water samples. Follows a normal distribution N( ), This represents the average value. Indicates standard deviation; S3022. The contribution percentage of pollution sources outputting agricultural fertilizers, soil organic nitrogen, and fecal sewage is multiplied by the total non-point source pollution percentage identified using three-dimensional fluorescence spectroscopy to obtain the actual contribution percentage of each non-point source pollution from different nitrogen pollution sources in surface water.

6. A combined isotope and biological tracer source tracing system for nitrogen pollution in water bodies, characterized in that, The method for tracing the source of nitrogen pollution in water bodies using a combination of isotopes and biological tracers as described in any one of claims 1-5 is implemented, including: The irrigation and drainage system survey module is used to survey the types and locations of irrigation and drainage ditches in the irrigation area to be studied, in order to identify different pollution source areas. The sample collection and analysis module is used to collect surface water and groundwater samples from irrigation and drainage ditches, analyze the samples, determine the fluorescence peak intensity, nitrate nitrogen isotope abundance, nitrate oxygen isotope abundance and fecal sterol concentration, and collect water pollutants. The surface water pollution source contribution analysis module is used to determine the contribution ratio of point source pollution sources and non-point source pollution sources, as well as the surface water pollution load, based on sample analysis results. The groundwater pollution source contribution analysis module is used to determine the contribution of groundwater non-point source pollution and groundwater pollution load based on sample analysis results.

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