Precise source tracing method for nitrogen pollution in river basin water body

Abstract

The application discloses a kind of basin water body nitrogen pollution multi-fingerprint coupling accurate tracing method, comprising: detecting the anion, cation and isotope data of end member sample, construct local fingerprint database, detect in-situ closed hydrological unit, obtain anion, cation and isotope data, calculate nitrate residual proportion, nitrate nitrogen denitrification fractionation coefficient and nitrate oxygen denitrification fractionation coefficient, collect water sample at sampling section, detect anion, cation and isotope data, remove non-nitrogen pollution source input, calculate nitrogen pollution source input, obtain corrected molar ratio, calculate nitrate residual proportion and corrected pollution source original isotope characteristic value, and match with local fingerprint database to obtain the type of pollution source. Thus, it can solve the distortion of isotope correction caused by general denitrification fractionation coefficient, utilize the whole process accurate correction of chlorine ion tracer fingerprint, and greatly improve the accuracy of pollution source determination result.

Description

Technical Field

[0001] This invention relates to the field of agricultural engineering technology, specifically to a method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling. Background Technology

[0002] Nitrate nitrogen is the main form of nitrogen pollution in watersheds and a key pollutant leading to eutrophication, excessive nitrate levels in groundwater, and degradation of aquatic ecosystems. Nitrate nitrogen pollution in watersheds is characterized by complex pollution sources, overlapping point and non-point source pollution, and strong heterogeneity in its spatiotemporal distribution. Accurate identification of nitrate nitrogen pollution sources is the core prerequisite and technological foundation for achieving source control and precise treatment of nitrogen pollution in watersheds. Stable isotope tracing technology, with its strong fingerprint characteristics and clear tracing pathways, has become the mainstream core technology for tracing the sources of nitrate nitrogen pollution in watersheds.

[0003] Currently, the mainstream nitrate nitrogen pollution tracing technology in this field uses stable isotopes of nitrate nitrogen and oxygen as the core tracer fingerprint. The technical principle is that nitrates from different sources have unique and heritable characteristic value ranges due to differences in their formation pathways, raw material isotopic composition, and previous biogeochemical fractionation processes.

[0004] The typical implementation process of this type of technology is as follows: First, end-member samples of various nitrate pollution sources in the target watershed are collected, and the nitrogen and oxygen isotope values ​​of the end-member samples are tested to construct a pollution source end-member fingerprint database. Then, sampling sections are set up in the target watershed, water samples are collected, and their measured nitrate nitrogen and oxygen isotope values ​​are tested. Given the prevalent denitrification biogeochemical process in water bodies, which leads to the enrichment of nitrogen and oxygen isotopes in residual nitrates and masks the original isotopic characteristics of the pollution source, existing technologies typically use water physicochemical indicators to qualitatively determine whether denitrification has occurred, and use the universally reported denitrification fractionation coefficient in the literature to correct the measured nitrate isotope values ​​in the water. Finally, the corrected isotope values ​​are compared with the pollution source end-member fingerprint database to determine the source of nitrate pollution in the water.

[0005] Some existing technologies introduce chloride ions as an auxiliary tracer indicator. By using the molar ratio of chloride ions to nitrates, they can help distinguish the types of pollution sources with overlapping isotopic values ​​and provide qualitative evidence of the occurrence of denitrification.

[0006] Analysis of the existing technical solutions reveals that the current isotope source tracing technology for nitrate nitrogen pollution in water bodies relies on the universal denitrification fractionation coefficient reported in the literature to complete isotope correction. This fails to achieve accurate in-situ matching between the fractionation coefficient and the actual water environment characteristics of the target watershed, resulting in serious distortion of the isotope fractionation correction results. This is the core reason for the insufficient accuracy and reliability of the source tracing results. Summary of the Invention

[0007] The present invention aims to at least partially solve the technical problems in the above-mentioned technologies.

[0008] Therefore, this invention discloses a method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling, characterized by comprising:

[0009] S1: Collect end-member samples from pollution sources in the target watershed and analyze the end-member samples. Data is used to construct fingerprint data of the pollution source and to construct a local fingerprint database of the target watershed;

[0010] S2: Within a preset monitoring period, the in-situ closed hydrological units within the target watershed are monitored to obtain the data at each monitoring time point. data;

[0011] S3: For the aforementioned in-situ closed hydrological unit, according to the formula Calculate the remaining nitrate percentage According to the formula Calculate the denitrification fractionation coefficient of nitrate nitrogen separately. and nitrate oxygen denitrification fractionation coefficient ,in,

[0012] for Monitor time points at all times molar ratio, for Monitor time points at all times molar ratio, for Monitor time points at all times data, for Monitor time points at all times data;

[0013] S4: Set up a sampling section in the target watershed, collect water samples from the target watershed for the complete hydrological cycle at the sampling section, and analyze the water samples. data;

[0014] S5: For the water sample, based on Molar ratio method for classifying non-nitrogen pollution source inputs and nitrogen pollution source input Based on the endmember hybrid model, non-nitrogenous pollution source inputs are removed. Calculate nitrogen pollution source input After correction molar ratio;

[0015] S6: For the water sample undergoing denitrification, according to the formula... Calculate the remaining nitrate percentage According to the formula Calculate the corrected original isotopic characteristic values ​​of the pollution source ,in,

[0016] For the local fingerprint database molar ratio, For the corrected molar ratio;

[0017] S7: The corrected original isotopic characteristic values ​​of the pollution source are... and the output of step S5 The molar ratio is matched with the local fingerprint database to determine the type of pollution source.

[0018] The method for precise source tracing of nitrogen pollution in water bodies using multi-fingerprint coupling disclosed in this invention has at least the following beneficial effects:

[0019] (1) By monitoring the time series of in-situ closed hydrological units in the target watershed, the residual proportion of nitrate during denitrification is accurately calculated by utilizing the absolute conservatism of chloride ions in geochemistry. A unique denitrification fractionation coefficient that perfectly matches the actual water environment characteristics of the target watershed is obtained by fitting. This completely replaces the general fractionation coefficient in the existing technology that deviates significantly from the actual situation of the target watershed, eliminates the core correction error caused by the deviation of the fractionation coefficient value, and fundamentally ensures the accuracy of the isotope correction results.

[0020] (2) Through The molar ratio method combined with the endmember mixture model accurately delineates and removes chloride ion interference from non-nitrogen pollution sources in the target watershed, yielding a corrected model that is only related to nitrogen pollution sources. The molar ratio eliminates the interference of non-nitrogen source chloride ions on the tracer results, providing unbiased basic data for the in-situ calibration of the denitrification fractionation coefficient, and also providing accurate auxiliary fingerprint data for subsequent pollution source matching.

[0021] (3) By using the denitrification fractionation coefficient specific to the target watershed, combined with the corrected The molar ratio was used to accurately calculate the remaining nitrate proportion, and the measured isotopic values ​​of nitrate in the water were corrected to obtain the original isotopic characteristic values ​​of the pollution source without interference from denitrification fractionation. This restored the original fingerprint characteristics of nitrate when it was discharged into the water body, avoiding fingerprint shifts caused by fractionation enrichment. Combined with the corrected values... By matching conservative fingerprints with a local fingerprint database, the type of nitrate pollution source in water bodies can be accurately determined, solving the technical problem that the pollution source matching results deviate significantly from the actual situation in existing technologies.

[0022] In addition, the multi-fingerprint coupling precise source tracing method for nitrogen pollution in water bodies disclosed in this invention may also have the following additional technical features:

[0023] Further, in step S2, within the preset monitoring period of 15 days, the data for days 0, 1, 3, 5, 7, 10, and 15 of the in-situ closed hydrological unit are monitored. data.

[0024] Further, in step S3, according to the formula The denitrification fractionation coefficients of nitrate nitrogen were calculated by fitting the data separately. and the nitrate oxygen denitrification fractionation coefficient Among them, the coefficient of determination of fit .

[0025] Further, in step S6, the water sample is screened to determine if denitrification has occurred in the water sample, specifically as follows:

[0026] Dissolved oxygen in water Oxidation-reduction potential ;

[0027] And the water body The data are positively correlated, and the slope is related to the nitrate nitrogen denitrification fractionation coefficient. and the nitrate oxygen denitrification fractionation coefficient ratio

[0028] And the water body and the output of step S5 The molar ratio is positively correlated.

[0029] Furthermore, in step S1, the pollution sources are classified into atmospheric dry and wet deposition, chemical nitrogen fertilizer, soil organic nitrogen, livestock and poultry manure, urban domestic sewage and rural domestic sewage.

[0030] Further, in step S4, the sampling cross-section is set in the target watershed, specifically as follows:

[0031] The sampling sections are set up along the main stream of the target watershed from upstream to downstream, at the watershed inlet, tributary confluence inlet, upstream and downstream of towns, or at the exit point.

[0032] Further, in step S5, The molar ratio is Non-nitrogen pollution source inputs classified as sea salt inputs , The molar ratio is Non-nitrogen pollution source inputs classified as rock salt inputs The remaining non-nitrogen pollution sources are classified as industrial inputs. .

[0033] Further, in step S7, the corrected original isotopic characteristic values ​​of the pollution source are... and the output of step S5 The molar ratio is matched with the local fingerprint database, specifically as follows:

[0034] Build The bivariate fingerprint spectrum will be used to correct the original isotopic characteristic values ​​of the pollution source. and the output of step S5 The molar ratio is superimposed and matched with the feature value range of the pollution source in the local fingerprint database. If it falls within the feature value range of the pollution source, the pollution source is determined to be the main source of nitrate in the water.

[0035] Additional features and advantages of this invention will be set forth in the description which follows, or may be learned by practicing the invention. Attached Figure Description

[0036] The technical solution and beneficial effects of the present invention will become apparent and readily understood from the following description in conjunction with the accompanying drawings, wherein:

[0037] Figure 1 This invention provides a bivariate fingerprint spectrum for qualitative identification of nitrate contamination using a multi-fingerprint coupled system.

[0038] Figure 2 This is a schematic diagram illustrating the verification of independent known source samples according to the present invention;

[0039] Figure 3 This is a schematic diagram illustrating the comparative verification of the contribution ratio of watershed pollution sources in this invention.

[0040] Figure 4 This is a schematic diagram of the variance decomposition of the uncertainty of the traceability results of the present invention. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0042] The method for precise source tracing of nitrogen pollution in water bodies by multiple fingerprint coupling disclosed in this invention will now be described with reference to the accompanying drawings.

[0043] A precise source tracing method for nitrogen pollution in watersheds using multi-fingerprint coupling includes:

[0044] S1: Collect end-member samples from pollution sources in the target watershed and analyze the end-member samples. Data is used to construct fingerprint data of pollution sources and to build a local fingerprint database for the target watershed;

[0045] S2: Within the preset monitoring period, in-situ closed hydrological units within the target watershed are monitored to obtain data at each monitoring time point. data;

[0046] S3: For in-situ closed hydrological units, according to the formula Calculate the remaining nitrate percentage According to the formula Calculate the denitrification fractionation coefficient of nitrate nitrogen separately. and nitrate oxygen denitrification fractionation coefficient ,in,

[0047] for Monitor time points at all times molar ratio, for Monitor time points at all times molar ratio, for Monitor time points at all times data, for Monitor time points at all times data;

[0048] S4: Set up sampling sections in the target watershed, collect water samples from the target watershed throughout the complete hydrological cycle at the sampling sections, and analyze the water samples. data;

[0049] S5: For water samples, based on Molar ratio method for classifying non-nitrogen pollution source inputs and nitrogen pollution source input Based on the endmember hybrid model, non-nitrogenous pollution source inputs are removed. Calculate nitrogen pollution source input After correction molar ratio;

[0050] S6: For denitrification water samples, according to the formula Calculate the remaining nitrate percentage According to the formula Calculate the corrected original isotopic characteristic values ​​of the pollution source ,in,

[0051] For local fingerprint database molar ratio, For the corrected molar ratio;

[0052] S7: Correct the original isotopic characteristic values ​​of the pollution source and the output of step S5 The molar ratio is matched with the local fingerprint database to determine the type of pollution source.

[0053] Specifically, in step S2, within a preset monitoring period of 15 days, the data for days 0, 1, 3, 5, 7, 10, and 15 of the in-situ closed hydrological unit are monitored. data.

[0054] Specifically, in step S3, according to the formula Calculate the denitrification fractionation coefficient of nitrate nitrogen separately. and nitrate oxygen denitrification fractionation coefficient Among them, the coefficient of determination of fit .

[0055] Specifically, in step S6, the water sample is screened to determine if denitrification has occurred.

[0056] Dissolved oxygen in water Oxidation-reduction potential ;

[0057] And the water body The data show a positive correlation, with the slope being related to the denitrification fractionation coefficient of nitrate nitrogen. and nitrate oxygen denitrification fractionation coefficient ratio

[0058] And the water body and the output of step S5 The molar ratio is positively correlated.

[0059] Specifically, in step S1, pollution sources are classified into atmospheric dry and wet deposition, chemical nitrogen fertilizer, soil organic nitrogen, livestock and poultry manure, urban domestic sewage and rural domestic sewage.

[0060] Specifically, in step S4, a sampling section is set in the target watershed, specifically as follows:

[0061] Sampling sections are set up along the main stream of the target basin from upstream to downstream, at the basin inlet, tributary confluence, upstream and downstream of towns, or at the exit point.

[0062] Specifically, in step S5, The molar ratio is Non-nitrogen pollution sources classified as sea salt input , The molar ratio is Non-nitrogen pollution source input classified as rock salt input The remaining non-nitrogen pollution sources are classified as industrial inputs. .

[0063] Specifically, in step S7, the corrected original isotopic characteristic values ​​of the pollution source are... and the output of step S5 The molar ratio is matched with the local fingerprint database, specifically as follows:

[0064] Build The bivariate fingerprint spectrum will be used to correct the original isotopic characteristic values ​​of the pollution source. and the output of step S5 The molar ratio is superimposed and matched with the feature value range of the pollution source in the local fingerprint database. If it falls within the feature value range of the pollution source, the pollution source is determined to be the main source of nitrate in the water.

[0065] Example

[0066] Relevant staff systematically investigated the pollution sources in the study area. In this embodiment, the pollution sources are classified into six categories: atmospheric dry and wet deposition, chemical nitrogen fertilizer, soil organic nitrogen, livestock and poultry manure, urban domestic sewage and rural domestic sewage.

[0067] Each pollution source's end-member samples were collected using a standardized method, following the requirements below. All end-member samples had at least three parallel samples:

[0068] For chemical nitrogen fertilizers, the mainstream nitrogen fertilizer varieties used in the study area were collected, with ≥3 replicates for each variety, and stored in a sealed and dry place at room temperature.

[0069] For livestock and poultry manure, fresh mixed manure samples were collected from large-scale farms, covering the mainstream livestock species in the watershed, with ≥3 parallel samples for each farm and ≥3 farms for each species, and stored at 4℃.

[0070] For soil organic nitrogen, topsoil samples were collected from 0 to 20 cm of different land use types in the watershed, avoiding areas recently fertilized. ≥5 sampling points were collected for each land use type, with 3 replicates for each sampling point. The samples were stored at 4℃.

[0071] For atmospheric dry and wet deposition, rain gauges and passive deposition samplers are used to collect samples during the wet and dry seasons, with ≥3 parallel samples per period. Sampling points avoid local pollution sources, and the samples are filtered and stored in the refrigerator away from light.

[0072] All end-member samples underwent standardized testing, and the testing methods and quality control standards are as follows:

[0073] For anions For testing using ion chromatography, the relative standard deviation (RSD) is <5%.

[0074] For cations In this regard, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for testing;

[0075] For nitrogen and oxygen isotopes In other words, the denitrifying bacteria method is used to remove the bacteria from the sample. Completely transformed The gas isotope mass spectrometer was used for testing, and the testing accuracy needed to meet the following requirements. ;

[0076] Statistical analysis of each endmember sample The data was used to establish a local fingerprint database.

[0077] Relevant staff screened the in-situ closed hydrological units and set up ≥3 parallel in-situ closed hydrological units and 2 backup in-situ closed hydrological units according to the following conditions:

[0078] There are no tributaries flowing into the area, no sewage outlets, no farmland runoff, and no groundwater recharge or any other external inputs.

[0079] The water body has a hydraulic retention time of ≥7 days, slow water flow, and hydrological conditions suitable for denitrification.

[0080] The environmental conditions of the water body, such as DO, ORP, water temperature, and pH, are consistent with the main river channel and key tributaries of the basin, and are representative of the entire basin.

[0081] The unit area is moderate, there is no human activity interference, and it is convenient for continuous sampling and monitoring.

[0082] For the selected in-situ closed hydrological units, continuous pre-monitoring was carried out for two days, with sampling and testing conducted at fixed times each day. If the coefficient of variation of concentration is <5% and the coefficient of variation of EC value is <5%, it is considered to meet the requirements of in-situ calibration.

[0083] Set up 15 days of continuous monitoring, with sampling time points on days 0, 1, 3, 5, 7, 10, and 15, and sampling at fixed times each day; if rainfall causes external input, immediately terminate the unit test and activate the backup parallel unit.

[0084] At each time point, two parallel samples were collected, and water temperature, DO, ORP, pH, and EC were tested simultaneously on-site; laboratory tests were also conducted simultaneously. .

[0085] based on Conservatism, according to the formula Calculate the remaining nitrate percentage According to the formula Calculate the denitrification fractionation coefficient of nitrate nitrogen separately. and nitrate oxygen denitrification fractionation coefficient .

[0086] Relevant staff set up sampling sections in the target watershed, from the upstream to the downstream of the watershed, according to hydrological units, covering the watershed entrance, the confluence of major tributaries, the upstream and downstream of towns, and the exit section, with one section set at intervals of 5 to 10 km.

[0087] The sections are set according to the land use type of the sub-basins, covering agricultural-dominated areas, urban-dominated areas, aquaculture-dominated areas, and forest background areas, with at least one cross section for each sub-basin;

[0088] Increase the density of monitoring points at sewage outlets flowing into rivers, sewage ditches of large-scale farms, farmland drainage outlets, and severely polluted river sections;

[0089] The natural background values ​​of the watershed were obtained by setting up a forest source area in the upper reaches of the watershed where there is no human activity interference.

[0090] Relevant staff conducted systematic sampling once each during the high-water season, normal-water season, and low-water season, with each sampling lasting for 3 consecutive days and at the same time each day;

[0091] An acrylic glass water sampler was used to collect surface water samples from 0.5m below the water surface. Two parallel samples were collected at each sampling point, and field blank and transport blank samples were set up simultaneously. The blank sample accounted for ≥10%.

[0092] It is important to note that the collected water samples should be pretreated and stored in the following manner:

[0093] Anion test samples were filtered using a 0.45μm filter membrane, stored at 4℃ in the dark, and tested within 7 days.

[0094] The cation test sample was filtered and then purified with analytical grade. Acidify to pH < 2 and store under cold.

[0095] Isotope test samples were filtered and then purified using analytical grade. Adjust the pH to <2, store frozen and protected from light, and complete the test within 15 days.

[0096] Relevant staff based on The molar ratio method distinguishes non-nitrogen sources such as sea salt input, rock salt dissolution, and industrial wastewater. and nitrogen pollution sources input ;

[0097] Based on the endmember mixing model, excluding non-nitrogen sources... Contribution, calculation of nitrogen source correlation Concentration, after correction Mole ratio.

[0098] Relevant staff members determined whether denitrification had occurred in the water samples, as follows:

[0099] Dissolved oxygen in water Oxidation-reduction potential ;

[0100] And the water body The data show a positive correlation, with the slope being related to the denitrification fractionation coefficient of nitrate nitrogen. and nitrate oxygen denitrification fractionation coefficient ratio

[0101] And the water body and the output of step S5 The molar ratio is positively correlated.

[0102] According to the formula Calculate the remaining nitrate percentage According to the formula Calculate the corrected original isotopic characteristic values ​​of the pollution source .

[0103] Using the corrected original isotopic characteristic values ​​of the pollution source After correction Using the molar ratio as an auxiliary conserved fingerprint, two sets of bivariate fingerprint patterns were constructed, and the results are attached. Figure 1 As shown:

[0104] exist Figure 1 middle, Bivariate fingerprinting, with the horizontal axis being... The vertical axis is The figure uses closed boxes of different colors and line types to mark the feature value ranges of six major pollution sources in the local fingerprint database. The solid black dots represent the corrected water samples. Initial value;

[0105] The corrected water sample fingerprint data is overlaid and matched with the pollution source feature value range of the local fingerprint database, based on the figure. The initial value falls within a certain range, and a determination is made accordingly.

[0106] like Figure 2 As shown, the Markov chain Monte Carlo (MCMC) method was used for iterative calculations, with three independent Markov chains and 1 million iterations (500,000 during the combustion period) and a refinement step size of 100. The Gelman-Rubin diagnostic method was used to verify the model's convergence; all parameters had Gelman-Rubin diagnostic values ​​<1.05, indicating good model convergence and reliable calculation results.

[0107] like Figure 3As shown, the model outputs the average contribution percentage and 95% confidence interval of each pollution source to nitrate nitrogen in the target watershed. The results are as follows: livestock and poultry manure 32.4% (95% CI: 28.7%-36.1%), rural domestic sewage 22.8% (95% CI: 19.5%-26.1%), chemical nitrogen fertilizer 21.5% (95% CI: 18.2%-24.8%), urban domestic sewage 12.3%, soil organic nitrogen 7.7%, and atmospheric dry and wet deposition 3.3%.

[0108] like Figure 4 As shown, the variance decomposition method was used to quantify the contribution of different influencing factors to the uncertainty of the traceability results of this invention. The horizontal bar chart results show that the contribution of each factor to the uncertainty of the traceability results from high to low is as follows: end-member fingerprint feature value 50%, denitrification fractionation coefficient 20%, sample test error 15%, end-member number 10%, and hydrological conditions 5%.

[0109] The results show that by calibrating the denitrification fractionation coefficient specific to the target watershed in situ, the present invention replaces the literature fractionation coefficient commonly used in existing technologies, reducing the uncertainty caused by the denitrification fractionation process from more than 40% in existing technologies to 20%, significantly reducing the error in the core calibration process, and fundamentally improving the stability and reliability of the source tracing results.

[0110] This embodiment fully implements the multi-fingerprint coupling precise source tracing method for nitrogen pollution in water bodies disclosed in this application. By in-situ calibration of the denitrification fractionation coefficient specific to the target watershed, unbiased correction of isotope values ​​is completed. The qualitative identification of pollution sources is completed by combining bivariate fingerprint spectrum. The contribution ratio is quantitatively calculated by Bayesian mixture model. The accuracy and reliability of the method are proved by two-dimensional verification and uncertainty analysis.

[0111] In summary, the multi-fingerprint coupling precise source tracing method for nitrogen pollution in watersheds disclosed in this invention has at least the following beneficial effects:

[0112] (1) By monitoring the time series of in-situ closed hydrological units in the target watershed, the residual proportion of nitrate during denitrification is accurately calculated by utilizing the absolute conservatism of chloride ions in geochemistry. A unique denitrification fractionation coefficient that perfectly matches the actual water environment characteristics of the target watershed is obtained by fitting. This completely replaces the general fractionation coefficient in the existing technology that deviates significantly from the actual situation of the target watershed, eliminates the core correction error caused by the deviation of the fractionation coefficient value, and fundamentally ensures the accuracy of the isotope correction results.

[0113] (2) Through The molar ratio method combined with the endmember mixture model accurately delineates and removes chloride ion interference from non-nitrogen pollution sources in the target watershed, yielding a corrected model that is only related to nitrogen pollution sources. The molar ratio eliminates the interference of non-nitrogen source chloride ions on the tracer results, providing unbiased basic data for the in-situ calibration of the denitrification fractionation coefficient, and also providing accurate auxiliary fingerprint data for subsequent pollution source matching.

[0114] (3) By using the denitrification fractionation coefficient specific to the target watershed, combined with the corrected The molar ratio was used to accurately calculate the remaining nitrate proportion, and the measured isotopic values ​​of nitrate in the water were corrected to obtain the original isotopic characteristic values ​​of the pollution source without interference from denitrification fractionation. This restored the original fingerprint characteristics of nitrate when it was discharged into the water body, avoiding fingerprint shifts caused by fractionation enrichment. Combined with the corrected values... By matching conservative fingerprints with a local fingerprint database, the type of nitrate pollution source in water bodies can be accurately determined, solving the technical problem that the pollution source matching results deviate significantly from the actual situation in existing technologies.

[0115] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling, characterized in that, include: S1: Collect end-member samples from pollution sources in the target watershed and analyze the end-member samples. Data is used to construct fingerprint data of the pollution source and to construct a local fingerprint database of the target watershed; S2: Within a preset monitoring period, the in-situ closed hydrological units within the target watershed are monitored to obtain the data at each monitoring time point. data; S3: For the aforementioned in-situ closed hydrological unit, according to the formula Calculate the remaining nitrate percentage According to the formula Calculate the denitrification fractionation coefficient of nitrate nitrogen separately. and nitrate oxygen denitrification fractionation coefficient ,in, for Monitor time points at all times molar ratio, for Monitor time points at all times molar ratio, for Monitor time points at all times data, for Monitor time points at all times data; S4: Set up a sampling section in the target watershed, collect water samples from the target watershed for the complete hydrological cycle at the sampling section, and analyze the water samples. data; S5: For the water sample, based on Molar ratio method for classifying non-nitrogen pollution source inputs and nitrogen pollution source input Based on the endmember hybrid model, non-nitrogenous pollution source inputs are removed. Calculate nitrogen pollution source input After correction molar ratio; S6: For the water sample undergoing denitrification, according to the formula... Calculate the remaining nitrate percentage According to the formula Calculate the corrected original isotopic characteristic values ​​of the pollution source ,in, For the local fingerprint database molar ratio, For the corrected molar ratio; S7: The corrected original isotopic characteristic values ​​of the pollution source are... and the output of step S5 The molar ratio is matched with the local fingerprint database to determine the type of pollution source.

2. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S2, within the preset monitoring period of 15 days, the data for days 0, 1, 3, 5, 7, 10, and 15 of the in-situ closed hydrological unit are monitored. data.

3. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S3, according to the formula The denitrification fractionation coefficients of nitrate nitrogen were calculated by fitting the data separately. and the nitrate oxygen denitrification fractionation coefficient Among them, the coefficient of determination of fit .

4. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S6, the water sample is screened to determine if denitrification has occurred, specifically as follows: Dissolved oxygen in water Oxidation-reduction potential ; And the water body The data are positively correlated, and the slope is related to the nitrate nitrogen denitrification fractionation coefficient. and the nitrate oxygen denitrification fractionation coefficient ratio And the water body and the output of step S5 The molar ratio is positively correlated.

5. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S1, the pollution sources are classified into atmospheric dry and wet deposition, chemical nitrogen fertilizer, soil organic nitrogen, livestock and poultry manure, urban domestic sewage and rural domestic sewage.

6. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S4, the sampling section is set in the target watershed, specifically as follows: The sampling sections are set up along the main stream of the target watershed from upstream to downstream, at the watershed inlet, tributary confluence inlet, upstream and downstream of towns, or at the exit point.

7. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S5, The molar ratio is Non-nitrogen pollution source inputs classified as sea salt inputs , The molar ratio is Non-nitrogen pollution source inputs classified as rock salt inputs The remaining non-nitrogen pollution sources are classified as industrial inputs. .

8. The method for precise source tracing of nitrogen pollution in watersheds using multi-fingerprint coupling as described in claim 1, characterized in that, In step S7, the corrected original isotopic characteristic values ​​of the pollution source are... and the output of step S5 The molar ratio is matched with the local fingerprint database, specifically as follows: Build The bivariate fingerprint spectrum will be used to correct the original isotopic characteristic values ​​of the pollution source. and the output of step S5 The molar ratio is superimposed and matched with the feature value range of the pollution source in the local fingerprint database. If it falls within the feature value range of the pollution source, the pollution source is determined to be the main source of nitrate in the water.

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