A quantitative calculation method for endogenous phosphorus pollution in watershed lakes

Abstract

This application discloses a method for quantitatively calculating endogenous phosphorus pollution in watershed lakes, relating to the field of nutrient source tracing technology for watershed lakes, including: determining the watershed boundary; collecting samples from media such as endogenous phosphorus output, exogenous phosphorus input, and lake water near the watershed; and obtaining the phosphate oxygen isotope values ​​δ of each pollution source and the source water of the lake. 18 O (PO4) ; Calculate the oxygen isotope value δ of phosphate 18 O (PO4) By combining the relative contribution rates of endogenous phosphorus output and exogenous phosphorus input calculated using Bayesian and hybrid endmember models with different types of land area data, the actual relative contribution rates of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of lakes in the watershed were determined. This application quantitatively calculates the actual relative contribution rate of endogenous phosphorus output to the phosphorus load of lakes based on traditional exogenous phosphorus tracing in watersheds, providing a supporting basis for accurate quantitative calculation of phosphorus in watersheds and lakes.

Description

Technical Field

[0001] This application relates to the field of nutrient source tracing technology for watershed lakes, and more specifically, to a method for quantitatively calculating endogenous phosphorus pollution in watershed lakes. Background Technology

[0002] Eutrophication of lakes has become a global problem, with excessive nitrogen and phosphorus inputs being the primary cause. In shallow eutrophic lakes, phosphorus plays a particularly prominent role in algal blooms. The increase in phosphorus concentration in lake waters mainly originates from external inputs from both point and non-point sources, as well as internal release from sediments. Studies have shown that when external phosphorus loads are intercepted, the continuous release of phosphorus from sediments has long-term, large-scale effects on water bodies, exacerbating eutrophication and algal blooms. Therefore, quantitatively tracing the contribution of exogenous phosphorus inputs and endogenous phosphorus outputs to phosphorus pollution in watershed lakes plays a crucial role in pollution management, restoration, and habitat recovery of lake ecosystems.

[0003] Due to the complexity of the environmental geochemical behavior of phosphorus transport from land to lakes, identifying and quantifying the sources of phosphorus in lakes based solely on concentration is difficult. Traditional methods for tracing the sources of phosphorus pollutants in lake waters include hydrological methods, geochemical methods, mathematical modeling techniques, and phosphate oxygen isotope techniques. However, considering the limitations of large data requirements, model stability, and high costs, the use of phosphate oxygen isotope techniques for identifying the sources and quantifying the contribution of phosphorus in lake waters has attracted widespread attention globally.

[0004] However, most existing studies using phosphate oxygen isotope technology for tracing focus on exogenous phosphorus. For example, patent application publication number CN 114496108A describes a method for tracing the source of phosphate in water based on phosphate oxygen isotope and water chemical characteristics. This method uses phosphate oxygen isotope technology combined with water chemical characteristics to identify and quantify the contribution ratio of each exogenous phosphorus source. However, it focuses on exogenous phosphorus input and lacks quantitative calculation research on the contribution of endogenous phosphorus output. This application, based on traditional watershed lake exogenous phosphorus tracing, can quantitatively calculate the actual relative contribution rate of endogenous phosphorus output to the phosphorus load of lake water, providing a supporting basis for accurate quantitative calculation of phosphorus in watershed lakes. Summary of the Invention

[0005] 1. Technical problems to be solved

[0006] To address the problem of accurately quantifying the contribution of endogenous phosphorus in watershed lake phosphorus pollution source tracing in existing technologies, this application provides a method for quantitatively calculating endogenous phosphorus pollution in watershed lakes. This method involves using the phosphate oxygen isotope value δ... 18 O (PO4)By substituting the relative contribution rates of endogenous phosphorus output and exogenous phosphorus input obtained from the Bayesian model and the hybrid endmember model into different types of land area data, the actual relative contribution rates of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of lakes in the watershed were determined.

[0007] 2. Technical Solution

[0008] The purpose of this application is achieved through the following technical solution.

[0009] This application provides a method for quantitatively calculating endogenous phosphorus pollution in a watershed lake, comprising: determining the watershed boundary, serving as the boundary for potential phosphorus source selection and the clipping boundary of a land use type map; collecting solid and liquid samples within the watershed boundary; wherein the solid samples include soil, sediment, and rock; and the liquid samples include sewage from piped pipes and lake water; obtaining the phosphate oxygen isotope values ​​of each sample; wherein the samples are divided into exogenous pollution sources and endogenous pollution sources; exogenous pollution sources include: crop farming, livestock and poultry farming, sewage from piped pipes, and rock weathering; endogenous pollution sources include: lake sediment; and the phosphate oxygen isotope values ​​include P0, P1, P2, P3, P4, and P5; wherein P1, P2, P3, P4, and P5 correspond to crop farming, etc. The data sources include livestock and poultry farming, pipeline sewage, rock weathering, and lake sediments; P0 corresponds to the phosphate oxygen isotope value of the lake water sample; the obtained phosphate oxygen isotope values ​​P0, P1, P2, P3, P4, and P5 are used as inputs, and the relative contribution rates of exogenous and endogenous pollution sources to phosphorus pollution in the watershed are calculated using pre-trained Bayesian and hybrid endmember models, respectively; the watershed boundary data and land use type data in vector format are imported into the geographic information system, and the land use type distribution map within the watershed boundary is obtained through cropping; based on the calculated relative contribution rates of endogenous and exogenous pollution to phosphorus pollution, and the obtained area of ​​each land use type, the actual contribution rates of endogenous and exogenous pollution to phosphorus pollution are calculated.

[0010] Furthermore, the relative contributions of endogenous and exogenous pollution to phosphorus pollution in the watershed were calculated using a Bayesian model, with the following formula:

[0011]

[0012] f n1 +f n2 +f n3 +f n4 +f n5 =1

[0013] in, P0 represents the phosphate oxygen isotope value of the lake water sample. The phosphate oxygen isotope values ​​P1, P2, P3, P4, and P5 represent crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution, respectively; f is estimated using a Bayesian model. n1 f n2 f n3 f n4 f n5 The value is used as the relative contribution rate of planting industry, livestock and poultry breeding industry, pipeline sewage, rock weathering and endogenous pollution.

[0014] Furthermore, the relative contributions of endogenous and exogenous pollution to phosphorus pollution in the watershed were calculated using a hybrid end-member model. The calculation formula is as follows: Construct a hybrid end-member model, and set the isotope value j of end-member i to X. ij The isotopic value j of source value k is S jk The fractionation coefficient of isotope j relative to source k is C. jk The residual is ε ij Set S jk Follows the mean μ jk The normal distribution, C jk Obeying λ jk The mean and the sum The variance follows a normal distribution; using the following formula, estimate the relative contribution rate P of pollution source k corresponding to each endmember. k :

[0015]

[0016] S jk ~N(μ) jk ,ω 2 jk )

[0017] C jk ~N(λ) jk ,τ 2 jk )

[0018] ε jk ~N(0,σ 2 j )

[0019] The estimated P k As the relative contribution rate of each pollution source to phosphorus pollution in the watershed.

[0020] Furthermore, the vector-formatted watershed boundary data and land use type data are imported into a geographic information system (GIS). A land use type distribution map within the watershed boundary is obtained through cropping. This process includes: importing the vector data of the watershed boundary and land use types into the GIS; using the GIS's cropping function, cropping the land use type data with the watershed boundary as the cropping boundary to obtain a land use type distribution map within the watershed boundary; and obtaining the following from the land use type distribution map: cultivated land area S1, grassland area S2, urban land area S3, bare rock land area S4, and lake water area S5; and assigning cultivated land area S1 to pollution sources from crop farming, grassland area S2 to pollution sources from livestock and poultry farming, urban land area S3 to pollution sources from piped sewage, bare rock land area S4 to pollution sources from rock weathering, and lake water area S5 to pollution sources from endogenous sources.

[0021] Furthermore, based on the calculated relative contribution rates of endogenous and exogenous pollution to phosphorus pollution, and the obtained land use area, the actual contribution rates of endogenous and exogenous pollution to phosphorus pollution are calculated, including: calculating the actual contribution rates F1, F2, F3, F4, and F5 of crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution to phosphorus pollution according to the following formulas: Among them, f ni The actual relative contribution rate of the i-th potential pollution source;

[0022] S mi Let S be the land use area corresponding to the i-th potential pollution source. T The sum of the areas of all land use types is used; F5 is taken as the actual contribution rate of endogenous pollution to phosphorus pollution in the basin lakes, and the sum of F1 to F4 is taken as the actual contribution rate of exogenous pollution to phosphorus pollution.

[0023] Further, obtaining the phosphate oxygen isotope values ​​of solid samples includes: adding nitric acid to soil, sediment, or rock samples that have been sieved through a 100-mesh screen and freeze-dried to obtain an extract; adding macroporous anion exchange resin to the extract and precipitating to obtain a purified phosphate solution; adding magnesium nitrate solution to the purified phosphate solution to generate silver phosphate precipitate; decomposing the silver phosphate precipitate into carbon monoxide and silver at a preset temperature; and using a thermocouple-elemental analyzer and an isotope ratio mass spectrometer to determine the oxygen isotope composition of carbon monoxide gas to obtain the phosphate oxygen isotope values ​​of soil, sediment, and rock samples.

[0024] Further, obtaining the phosphate oxygen isotope value of the liquid sample includes: filtering the sewage or lake water sample through a cellulose acetate membrane to remove particulate matter; adding sodium hydroxide solution to the filtered water sample, followed by magnesium nitrate solution, to form a phosphate-magnesium hydroxide coprecipitate; subjecting the phosphate-magnesium hydroxide coprecipitate to dissolution, precipitation, and cation removal processes to obtain a purified phosphate solution; adding silver nitrate solution to the purified phosphate solution to generate silver phosphate precipitate; and decomposing the silver phosphate precipitate into carbon monoxide and silver at a preset temperature. The oxygen isotope value of the liquid sample is obtained by measuring the oxygen isotope composition of the carbon monoxide gas using a thermocouple-elemental analyzer and an isotope ratio mass spectrometer.

[0025] Furthermore, the precipitation methods include two types: AMP (magnesium ammonium phosphate, NH4MgPO4) precipitation and MAP (magnesium ammonium phosphate, MgNH4PO4) precipitation. These two precipitants can selectively precipitate and separate phosphate ions from complex matrices during sample processing, thereby achieving purification and enrichment.

[0026] Furthermore, when pretreating liquid samples (sewage, lake water), it is necessary to first use a cellulose acetate membrane to remove particulate matter from the water. The membrane should have a pore size between 0.2 μm and 0.45 μm. This range of membrane size effectively removes suspended particles from the water sample, reducing interference from solid impurities; at the same time, the pore size is not too small to avoid problems such as slow filtration rates or membrane clogging, thus balancing complete filtration with ease of operation.

[0027] Furthermore, in the pretreatment of solid samples (soil, sediment, rock), phosphate ions need to be extracted with nitric acid. The preferred range of nitric acid concentration is 1 mol / L to 1.5 mol / L. This concentration range of nitric acid can effectively dissolve and extract inorganic phosphorus compounds in the sample, ensuring complete extraction; on the other hand, the acidity is not too high, avoiding corrosion of instruments or the introduction of excessive impurities.

[0028] 3. Beneficial effects

[0029] Compared to existing technologies, the advantages of this application are:

[0030] By obtaining phosphate oxygen isotope values ​​δ from different pollution sources (crop farming, livestock and poultry farming, pipeline sewage, rock weathering, and lake sediments) and lake water within the watershed. 18 O (PO4) By substituting these values ​​into the Bayesian model and the hybrid endmember model for calculation, the relative contribution rates of endogenous phosphorus output and exogenous phosphorus input to phosphorus pollution in the watershed can be accurately estimated, solving the problem that traditional methods are unable to quantitatively distinguish the contributions of endogenous and exogenous phosphorus.

[0031] By using GIS technology to crop watershed boundary and land use type data, area data of different land use types (arable land, grassland, urban land, bare rock land, and lake water surface) within the watershed are obtained. Combined with the relative contribution rates of endogenous and exogenous phosphorus, the actual contribution rates of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of watershed lakes can be calculated, thus achieving accurate quantification of endogenous phosphorus pollution.

[0032] Advanced instruments such as thermocouple-elemental analyzer and isotope ratio mass spectrometer were used to extract, purify, and analyze phosphates from solid samples such as soil, sediment, and rock, as well as liquid samples such as sewage and lake water. 18 O (PO4) This measurement ensures the accuracy and reliability of the sample analysis data.

[0033] δ 18 O (PO4) As a tracer indicator, it is used to analyze pollution sources by means of mathematical models such as Bayesian models and hybrid endmember models. It combines the advantages of tracer and model, makes up for the shortcomings of a single tracer or a single model in clarifying complex pollution sources, and improves the accuracy and reliability of quantitative calculation of endogenous and exogenous phosphorus contributions. Attached Figure Description

[0034] Figure 1 This is a technical roadmap for a quantitative calculation method of endogenous phosphorus pollution in a watershed lake according to this application;

[0035] Figure 2 This is a schematic diagram showing the proportion of internal and external phosphorus sources in this application. Detailed Implementation

[0036] The present application will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] A method for quantitatively calculating endogenous phosphorus pollution in a watershed lake includes the following steps: determining the watershed boundary; collecting samples from media such as endogenous phosphorus output, exogenous phosphorus input, and lake water near the watershed; and obtaining the phosphate oxygen isotope values ​​δ for each pollution source and the source water of the lake. 18 O (PO4) ; Calculate the oxygen isotope value δ of phosphate 18 O (PO4) By substituting the relative contribution rates of endogenous phosphorus output and exogenous phosphorus input obtained from the Bayesian model and the hybrid endmember model into different types of land area data, the actual relative contribution rates of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of lakes in the watershed were determined.

[0039] The above-mentioned technical method incorporates the phosphate oxygen isotope value δ 18 O(PO4) By combining various types of land area data, hybrid endmember models, and Bayesian models, and by matching different types of land area data with potential phosphorus source types to calculate contribution rates, the actual contribution rates of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of the watershed can be obtained.

[0040] Specifically, determining the watershed boundary and sampling: First, the watershed boundary needs to be determined according to the research objectives. Determining the watershed boundary has two main purposes: ② to serve as a boundary for selecting potential phosphorus sources, i.e., to collect samples of possible phosphorus pollution sources within this boundary, such as crop soil, livestock manure, sewage, rocks, and lake sediments; ③ for subsequent steps using GIS to crop land use type maps to calculate the area of ​​different land use types.

[0041] After determining the watershed boundary, samples from major potential phosphorus pollution sources need to be collected within the boundary. These sources include: crop farming (corresponding to soil samples), livestock and poultry farming (corresponding to manure and wastewater samples), piped sewage (corresponding to domestic and industrial wastewater samples), rock weathering (corresponding to rock samples), and endogenous pollution from lakes (corresponding to sediment samples). The selection of sampling points needs to comprehensively consider the distribution characteristics of the pollution sources and the representativeness of the samples.

[0042] In addition, water samples need to be collected from the lake to obtain the oxygen isotope values ​​of phosphate in the lake water. To ensure the reliability of the lake water source tracing, the water sampling points must be selected downstream of the direction of the exogenous phosphorus input flow, so that the collected water samples can represent the lake water condition after the mixture of exogenous and endogenous phosphorus.

[0043] Compared to previous watershed phosphorus tracing studies, this technical approach offers a more comprehensive and systematic sample collection method, considering not only exogenous phosphorus input but also emphasizing the contribution of endogenous phosphorus release. In subsequent tracing analysis, by integrating phosphate oxygen isotope tracing and mathematical models, the relative contributions of endogenous and exogenous phosphorus can be more accurately quantified, allowing for the estimation of their actual contribution to the phosphorus load in lake waters, thereby significantly improving the accuracy of watershed lake phosphorus tracing.

[0044] Sample Analysis and Data Acquisition: Phosphate Oxygen Isotope Values ​​of Soil, Sediment, and Rock Samples The acquisition steps are as follows: Soil, sediment, and rock samples were freeze-dried to remove moisture, then sieved through a 100-mesh sieve to homogenize the sample particle size for easier subsequent extraction. 20g of the pretreated sample was weighed into an Erlenmeyer flask, and 120ml of 1mol / L nitric acid (HNO3) was added. The mixture was shaken for 24 hours to fully dissolve the phosphate in the nitric acid solution. Macroporous resin was added to the extract to remove organic matter. Then, a series of steps including AMP (ammonium phosphomolybdate precipitation), MAP (magnesium phosphomolybdate precipitation), and cation removal were performed to further purify the phosphate ions in the solution. Magnesium nitrate solution was added to the purified solution to displace the bright yellow silver phosphate (Ag3PO4) precipitate. The precipitate was collected by centrifugation, washed, and dried to obtain a solid silver phosphate sample. An appropriate amount of silver phosphate sample was taken, and its δ18O value was determined using a high-temperature pyrolysis-stable isotope mass spectrometer (TC / EA-IRMS) to obtain the δ18O values ​​of the soil, sediment, and rock samples. data.

[0045] Phosphate oxygen isotope values ​​of water samples The acquisition steps are as follows: The collected water sample was filtered through a 0.45 μm filter membrane to remove suspended particulate matter. 1 mol / L sodium hydroxide and 0.5 mol / L magnesium nitrate solution were added to the filtered water sample at a volume ratio of 1% to form a phosphate-magnesium hydroxide coprecipitate. After standing for several hours, the precipitate was collected by centrifugation. Referring to soil sediment samples, the coprecipitate sample was purified and silver phosphate was precipitated. An appropriate amount of silver phosphate sample was taken, and its δ0.05 value was determined using TC / EA-IRMS. 18 O value, obtained from water sample data.

[0046] Specifically, combining phosphate oxygen isotope values Using a hybrid endmember model and a Bayesian model, we can calculate the relative contribution rate f of different potential phosphorus pollution sources. ni The formula used is as follows:

[0047]

[0048] f n1 +f n2 +f n3 +f n4 +f n5 =1

[0049]

[0050] S jk ~N(μ) jk ,ω 2 jk )

[0051] C jk ~N(λ)jk ,τ 2 jk )

[0052] ε jk ~N(0,σ 2 j )

[0053] Wherein, δ 18 O (PO4-river) For lake water δ 18 O (PO4) Value; δ 18 O (PO4-n1) δ 18 O (PO4-n1) δ 18 O (PO4-n1) δ 18 O (PO4-n1) δ 18 O (PO4-n1) δ represents potential pollution sources such as crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution. 18 O (PO4) Value; where f n1 f n2 f n3 f n4 f n5 These represent the relative contribution rates of potential pollution sources such as crop farming, livestock and poultry breeding, piped sewage, rock weathering, and endogenous pollution; X ij Let j be the isotopic value of endmember i; P k Estimated by the model; S jk The isotopic value j of source value k follows a mean μ jk The normal distribution of C; jk The fractionation coefficient of isotope j with respect to source k is denoted by λ. jk and The mean is normally distributed; ε ij The residuals describe the additional between-observation variance not described by the model. Since only the oxygen phosphate isotope is used, the value of j in the equation is 1.

[0054] Specifically, land use type area calculation: Collect land use type vector data and watershed boundary vector data for the study area, ensuring the coordinate systems of the two types of data are consistent. Import the watershed boundary data and land use type data into ArcGIS software, displaying them as two separate layers. Using ArcGIS's "Clip" tool, clip the land use type layer with the watershed boundary layer as the clipping range. The resulting land use type layer after clipping is the land use distribution map within the study watershed area. Open the attribute table of the clipped land use type layer, add a new field "Area," and use ArcGIS's "Computational Geometry" function to calculate the area of ​​each land use type polygon, in square kilometers (km²). Export the attribute table to an Excel file, summarizing the area data for different land use types.

[0055] When calculating land use area, different land use types correspond to different phosphorus pollution sources. Specifically, cultivated land area represents pollution sources from crop farming, grassland area represents pollution sources from livestock and poultry farming, urban construction land area represents pollution sources from piped sewage (including domestic sewage and industrial wastewater), unused land (such as bare rock land) area represents pollution sources from rock weathering, and lake water area represents endogenous pollution. Because forest land has excellent soil and water conservation functions and a significant effect on phosphorus interception, it is generally not considered a phosphorus pollution source. Therefore, forest land area can be excluded from the pollution source area calculation. To facilitate subsequent pollution source analysis, the area data for different land use types can be categorized in an Excel summary table. For example, cultivated land, grassland, urban construction land, unused land, and lake water bodies can be categorized as crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution, respectively. Through the above GIS analysis and data processing steps, we can accurately obtain area data of different land use types in the study watershed and establish a connection with the corresponding pollution source types, providing important area parameters for subsequent pollution source analysis and calculation of lake phosphorus load contribution rate.

[0056] Specifically, the actual contribution rate F of multiple potential pollution sources i The calculation formula is as follows:

[0057]

[0058] Among them, F N1 F N2 F N3 F N4 F N5F1, F2, F3, F4, and F5 represent the actual contribution rates of potential pollution sources such as crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution combined with land use data; S represents the actual relative contribution rates of these potential pollution sources combined with land use data. m1 S m2 S m3 S m4 S m5 S represents the land use area of ​​cultivated land, grassland, urban construction land, unused land, and lake water bodies, respectively; T It is the sum of the areas of all land use types.

[0059] Specifically, F5 represents the actual relative contribution rate of endogenous phosphorus output (i.e., release from lake sediments) to the phosphorus load of lakes in the basin, and the sum of F1+F2+F3+F4 represents the actual relative contribution rate of exogenous phosphorus input (including crop farming, livestock and poultry farming, pipeline sewage and rock weathering) to the phosphorus load of lakes in the basin.

[0060] Compared with previous watershed phosphorus tracing studies, this application comprehensively considers both endogenous and exogenous phosphorus pollution and quantitatively calculates their respective actual contributions to lake phosphorus load, overcoming the shortcomings of traditional studies that only focus on exogenous phosphorus input or qualitatively describe endogenous phosphorus release. By combining pollution source apportionment with land use analysis, a weighted average method is used to multiply the relative contribution rate of each pollution source by the area data of its corresponding land use type and divide by the total area to obtain the actual contribution rate of each pollution source. This method not only considers the relative importance of different pollution sources but also their spatial distribution characteristics in the watershed, making the calculation results more accurate and reliable. The calculation results quantitatively provide the actual relative contributions of endogenous phosphorus output and exogenous phosphorus input to the phosphorus load of watershed lakes, allowing for a direct comparison of the relative importance of endogenous and exogenous phosphorus pollution, providing an important basis for precise source tracing and control of watershed phosphorus pollution. Relevant departments can then formulate targeted measures such as dredging of endogenous sediment and control of exogenous pollution to improve the accuracy and effectiveness of eutrophication prevention and control in watershed lakes.

[0061] Example 2

[0062] Taking the Poyang Lake basin as an example, the Poyang Lake basin is the collective name for the basins of five rivers—the Gan River, Fu River, Xinjiang River, Rao River, and Xiu River—and the Poyang Lake area, with a basin area of ​​166,835.74 square kilometers. A precise quantitative calculation method for the contribution of endogenous phosphorus pollution to lakes within the basin includes the following steps: Major potential phosphorus pollution sources are collected, including crop farming, livestock and poultry farming, piped sewage (domestic wastewater and industrial wastewater), rock weathering, and lake sediments. Soil, water, rock, and sediment samples are collected accordingly. The phosphate oxygen isotope values ​​(δ¹⁸O) of each pollution source and the source water of the lake are obtained. 18O (PO4) ), as shown in Table 1; different types of land area data can be obtained from globeland30.org or the Resource and Environmental Science and Data Platform (https: / / www.resdc.cn) by analyzing phosphate oxygen isotope values ​​(δ¹⁸O). 18 O (PO4) By substituting the relative contribution rates of endogenous phosphorus output and exogenous phosphorus input obtained from the Bayesian model and the hybrid endmember model, and combining them with different types of land area data, the actual relative contribution rates of endogenous phosphorus output and exogenous phosphorus input were determined, thereby quantitatively analyzing the impact of endogenous phosphorus output and exogenous phosphorus input on the phosphorus load of watershed lakes. Figure 2 The diagram shows the proportion of internal and external phosphorus sources in this application, as shown in Tables 2 and 3.

[0063] Table 1

[0064]

[0065] Table 2

[0066]

[0067]

[0068] Table 3

[0069]

[0070] In Table 1, the average phosphorus and oxygen isotope values ​​of Poyang Lake are 14.44±1.63‰, while the average phosphorus and oxygen isotope values ​​of planting, livestock and poultry farming, piped sewage (domestic wastewater and industrial wastewater), rock weathering, and lake sediments are 15.58±0.17‰, 18.03±2.21‰, 12.4±0.8‰, 8.2±1.05‰, and 13.7±0.46‰, respectively.

[0071] Table 2 shows that the Poyang Lake basin area is 166,835.74 km². 2 Of this, arable land area is 48,416.42 km². 2 , accounting for 29.02%; grassland area is 2266.94 km². 2 It accounts for 1.36%; the urban construction land area is 10282.07 km². 2 It accounts for 6.16%; the forest area is 95,239.5 km². 2 It accounts for 57.09%; the water area is 9392.46 km². 2 , accounting for 5.63%; the area of ​​unused land is

[0072] 1238.35km 2 , accounting for 0.74%.

[0073] In Table 3, the actual relative contributions of exogenous phosphorus inputs to the phosphorus load of Poyang Lake, including crop farming, livestock and poultry breeding, piped sewage (domestic wastewater and industrial wastewater), and rock weathering, were 69.03%, 4.25%, 13.09%, and 1.09%, respectively, with an exogenous phosphorus input contribution rate of 87.46%; the endogenous phosphorus output contribution rate was 12.54%.

[0074] The foregoing illustrative description of the invention and its embodiments is not restrictive and can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. The accompanying drawings are only one embodiment of the invention, and the actual structure is not limited thereto. No reference numerals in the claims should limit the scope of the claims. Therefore, if a person skilled in the art, inspired by this description, designs a similar structure and embodiment without departing from the spirit of the invention, such design should fall within the scope of protection of this patent. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" preceding an element does not exclude the inclusion of "a plurality" of that element. Multiple elements stated in the product claims can also be implemented by a single element through software or hardware. The terms "first," "second," etc., are used to indicate names and do not indicate any specific order.

Claims

1. A method for quantitatively calculating endogenous phosphorus pollution in a watershed lake, comprising: Determine the watershed boundary as the boundary for potential phosphorus source selection and the clipping boundary for the land use type map; Solid and liquid samples were collected separately within the watershed boundary. Solid samples included soil, sediment, and rocks; liquid samples included sewage from pipes and lake water. Obtaining the phosphate oxygen isotope values of each sample; wherein, the samples are divided into exogenous pollution sources and endogenous pollution sources; the exogenous pollution sources include: planting industry pollution sources, livestock and poultry breeding industry pollution sources, pipeline sewage pollution sources and rock weathering pollution sources; the endogenous pollution sources include: lake sediment pollution sources; the phosphate oxygen isotope values include 、 、 、 、 and ; wherein, 、 、 、 and correspond to planting industry, livestock and poultry breeding industry, pipeline sewage, rock weathering and lake sediment, respectively; correspond to the phosphate oxygen isotope values of the lake water body samples; The obtained phosphate oxygen isotope values , , , , and As input, the relative contribution rates of exogenous and endogenous pollution sources to phosphorus pollution in the watershed are calculated using pre-trained Bayesian models and hybrid endmember models, respectively. Import vector-format watershed boundary data and land use type data into a geographic information system, and obtain a land use type distribution map within the watershed boundary by cropping. Based on the calculated relative contribution rates of endogenous and exogenous pollution to phosphorus pollution, and the obtained land use area, the actual contribution rates of endogenous and exogenous pollution to phosphorus pollution are calculated. Based on the calculated relative contribution rates of endogenous and exogenous pollution to phosphorus pollution, and the obtained land use area, the actual contribution rates of endogenous and exogenous pollution to phosphorus pollution are calculated, including: Calculate the actual contribution rates of crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution to phosphorus pollution using the following formulas. , , , , : ;in, This indicates the actual contribution rate of each potential pollution source; in, The actual relative contribution rate of the i-th potential pollution source; ； Let i be the land use type area corresponding to the i-th potential pollution source. This is the sum of the areas of all land use types; Will As the actual contribution rate of endogenous pollution to phosphorus pollution in the basin's lakes, to The sum of these values ​​represents the actual contribution rate of exogenous pollution to phosphorus pollution.

2. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 1, characterized in that: The relative contributions of endogenous and exogenous pollution to phosphorus pollution in the watershed were calculated using a Bayesian model, and the formulas are as follows: ； ； in, P0 represents the phosphate oxygen isotope value of the lake water sample. , , , , Phosphate oxygen isotope values ​​representing crop farming, livestock and poultry farming, piped sewage, rock weathering, and endogenous pollution, respectively. , , , and ; Estimate using Bayesian model The value is used as the relative contribution rate of planting industry, livestock and poultry breeding industry, pipeline sewage, rock weathering and endogenous pollution.

3. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 2, characterized in that: The relative contributions of endogenous and exogenous pollution to phosphorus pollution in the watershed were calculated using a hybrid endmember model, and the formulas are as follows: Construct a hybrid endmember model, and set the isotope value j of endmember i as... The isotopic value j of source value k is ; The fractionation coefficient of isotope value j with respect to source value k is The residual is ; set up Follow the mean The normal distribution Obey The mean and the sum The variance follows a normal distribution. The relative contribution rate of pollution source k corresponding to each end-member is estimated using the following formula. : ； ； ； ； The estimated As the relative contribution rate of each pollution source to phosphorus pollution in the watershed.

4. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 3, characterized in that: Importing vector-format watershed boundary data and land use type data into a geographic information system, and then cropping the data to obtain a land use type distribution map within the watershed boundary, including: Import vector data of watershed boundaries and land use types into the geographic information system; Using the cropping function of a geographic information system, land use type data is cropped with the watershed boundary as the cropping boundary to obtain a land use type distribution map within the watershed boundary. Obtained from the land use type distribution map: Cultivated land area grassland area Urban land area Area of ​​bare rock and lake water area ; arable land area Corresponding to pollution sources from agriculture, grassland area Corresponding to pollution sources from livestock and poultry farming, urban land area Corresponding to the sewage pollution source in the pipeline, the area of ​​bare rock land Corresponding to rock weathering pollution sources, lake water area Corresponding to endogenous pollution.

5. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 1, characterized in that: Obtain the phosphate oxygen isotope values ​​of solid samples, including: A nitric acid solution is added to soil, sediment, or rock samples that have undergone sieving and freeze-drying to obtain an extract. The extract was subjected to precipitation treatment to obtain a purified phosphate solution; Adding magnesium nitrate solution to the purified phosphate solution produces silver phosphate precipitate. Silver phosphate precipitate was decomposed into carbon monoxide and silver at a preset temperature. The oxygen isotope values ​​of phosphate in soil, sediment and rock samples were obtained by measuring the oxygen isotope composition of carbon monoxide gas using a thermocouple-elemental analyzer and isotope ratio mass spectrometer.

6. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 5, characterized in that: Obtain the phosphate oxygen isotope values ​​of liquid samples, including: Sewage or lake water samples are filtered through cellulose acetate membranes to remove particulate matter from the water. After adding sodium hydroxide solution to the filtered water sample, magnesium nitrate solution is then added to form a phosphate-magnesium hydroxide coprecipitate. The phosphate-magnesium hydroxide coprecipitate was purified to obtain a purified phosphate solution. Adding silver nitrate solution to the purified phosphate solution produces silver phosphate precipitate. Silver phosphate precipitate was decomposed into carbon monoxide and silver at a preset temperature. The oxygen isotope value of the liquid sample was obtained by measuring the oxygen isotope composition of the carbon monoxide gas using a thermocouple-elemental analyzer and an isotope ratio mass spectrometer.

7. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 5 or 6, characterized in that: Precipitations include AMP precipitation and MAP precipitation.

8. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 7, characterized in that: Acetate cellulose with a diameter of 0.2μm to 0.45μm is used.

9. The method for quantitatively calculating endogenous phosphorus pollution in watershed lakes according to claim 8, characterized in that: The concentration of nitric acid ranges from 1 mol / L to 1.5 mol / L.

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