A method for calculating input and output fluxes of heavy metals in cultivated soil

Abstract

This invention belongs to the field of soil environmental monitoring and pollution assessment technology, specifically involving a method for calculating the input and output fluxes of heavy metals in arable land soil. The method includes the following steps: S1, basic data collection and preprocessing of the study area; S2, calculation of multi-source heavy metal input fluxes; S3, calculation of multi-pathway heavy metal output fluxes; S4, dynamic correction of soil physicochemical properties; and S5, input-output balance analysis and risk assessment. This invention, by pioneering the use of agricultural product exports (annual output minus local consumption) as the core output for quantitative accounting, accurately distinguishes between the internal circulation of heavy metals within the production area and the output from outside the region. It is particularly suitable for major production areas of specialty agricultural products with high export rates, such as tea, fruits, vegetables, and medicinal herbs. The calculation results can truly reflect the actual balance state of heavy metals in the regional arable land soil.

Description

Technical Field

[0001] This invention belongs to the field of soil environmental monitoring and pollution assessment technology, specifically relating to a method for calculating the input and output fluxes of heavy metals in arable land soil. Background Technology

[0002] Heavy metal pollution in arable land soil is a significant issue affecting the quality and safety of agricultural products and the health of the ecological environment. The heavy metal content in the topsoil of arable land is in a dynamic equilibrium, and its changes mainly depend on the input and output processes of heavy metals in the environment. Accurately calculating the input and output fluxes of heavy metals in arable land soil is crucial for identifying pollution sources, assessing pollution risks, and developing prevention and control measures.

[0003] In existing technologies, the methods for calculating heavy metal fluxes in arable land soil mainly suffer from the following shortcomings, among which the systematic bias in the calculation of output items has become the core bottleneck restricting the accuracy of the calculation: 1. The export channels have fundamental flaws and have not been systematically incorporated into the core export items of agricultural products. Existing technologies either completely ignore the impact of agricultural harvesting on heavy metal output or simply use total agricultural output as the output base, failing to systematically quantify agricultural exports (annual output minus local consumption) as a core output item. In reality, heavy metals in agricultural products consumed within the production area (including those for residential consumption, feed processing, and local deep processing) return to the arable land ecosystem through methods such as returning human and animal manure to the field, composting kitchen waste, and returning processing waste to the field; they do not truly leave the study area. Only core specialty agricultural products sold to other provinces or exported permanently remove heavy metals from the regional arable land system. For major production areas of core specialty agricultural products such as tea, fruits, vegetables, and medicinal herbs, the export rate is generally as high as 70%-95% or more. Existing methods that include all total output in the output flux lead to a significant overestimation of the output flux, resulting in a directional error in the net flux calculation and failing to accurately reflect the accumulation or loss trend of heavy metals in arable land soil.

[0004] 2. The input pathways are not fully considered, and the contribution of the internal cycle of the agricultural ecosystem is ignored. Most studies focus on external inputs such as atmospheric dry and wet deposition and industrial fly ash, while neglecting the material cycling processes within the agricultural ecosystem, particularly the heavy metal inputs from livestock manure and straw return to the fields. With the rapid development of livestock farming and the continuous increase in straw return rates in my country, these two pathways have become significant sources of heavy metal input to arable land soil. Ignoring them leads to a serious underestimation of input fluxes.

[0005] 3. Other aspects of the output pathway are missing, failing to cover key processes of soil erosion. Besides agricultural product exports, only surface runoff exports are typically considered, neglecting the contribution of soil erosion to heavy metal exports. In sloping farmland and hilly areas, soil erosion is one of the main pathways for heavy metal loss. The amount of heavy metals carried by eroded sediment is often much higher than that dissolved in surface runoff. Ignoring this pathway will lead to serious distortion in the calculation of output fluxes.

[0006] 4. Lack of dynamic correction mechanism, unable to reflect soil spatial heterogeneity. Most existing methods use fixed flux calculation parameters and do not consider the influence of soil physicochemical properties (such as pH, organic matter content, and clay content) on heavy metal migration and transformation. The solubility, adsorption capacity, and bioavailability of heavy metals vary significantly across different soil types. Fixed parameters cannot reflect this spatial heterogeneity, leading to large discrepancies between calculated results and actual conditions.

[0007] 5. The calculation accuracy of volatile heavy metals is low, and localized parameter correction has not been performed. For volatile heavy metals such as mercury, most existing methods directly apply general emission flux equations without localizing them to take into account the meteorological conditions and soil characteristics of the study area. Soil mercury emission flux is affected by various factors such as light, temperature, and humidity, and the applicability of general equations to different regions is limited, resulting in large errors in the calculation of mercury output flux.

[0008] Therefore, there is an urgent need to develop a method for calculating the input and output fluxes of heavy metals in arable land soil that is tailored to the characteristics of major agricultural product producing areas, comprehensively covers the input and output processes, and has dynamic correction capabilities, in order to solve the above-mentioned problems of existing technologies and provide a scientific basis for the precise prevention and control of heavy metal pollution in arable land soil. Summary of the Invention

[0009] The purpose of this invention is to provide a method for calculating the input and output fluxes of heavy metals in arable land soil. By comprehensively considering the material cycling process within the agricultural ecosystem, introducing dynamic correction coefficients for soil physicochemical properties, and improving the calculation model for volatile heavy metals, the method achieves accurate calculation of heavy metal fluxes in arable land soil, providing a scientific basis for soil pollution risk assessment and prevention.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for calculating the input and output fluxes of heavy metals in arable land soil, comprising the following steps: S1. Basic data collection and preprocessing in the study area: Collect soil physicochemical properties data, meteorological data, agricultural production chain data, industrial emission data and hydrological data of cultivated land in the study area, and perform standardized preprocessing. S2. Calculation of multi-source heavy metal input flux: Calculate the atmospheric dry and wet deposition input flux, fly ash input flux, and comprehensive agricultural production input flux, respectively. The comprehensive agricultural production input flux includes irrigation water input flux, fertilizer input flux, pesticide input flux, livestock and poultry manure return to the field input flux, and straw return to the field input flux. S3. Calculation of heavy metal output flux through multiple pathways: Calculate the output flux of surface runoff, output flux of agricultural products sold abroad, and output flux of soil erosion. For mercury, calculate the output flux of mercury exchange at the soil-atmosphere interface. S4. Dynamic Correction of Soil Physicochemical Properties: Based on soil pH, organic matter content, and clay content, determine the migration and transformation correction coefficients for each heavy metal element. Based on experimentally measured soil pH, organic matter content, and clay content, determine the input availability correction coefficients for each heavy metal element. Only all input fluxes obtained in step S2 are corrected. The correction coefficients only reflect the effective proportion of heavy metals entering the soil that can participate in the soil ecosystem cycle and do not affect the output fluxes that have left the soil. S5. Input-output balance analysis and risk assessment: Calculate the corrected total input and output of heavy metals to obtain the net flux, analyze the dynamic balance of heavy metals in arable land soil, and assess the pollution risk based on the net flux and soil background values.

[0011] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the atmospheric dry and wet deposition input flux in step S2 is as follows: ; In the formula, The flux of a certain heavy metal element i into the topsoil via dry and wet deposition is expressed in kg / a. The total mass of dry and wet sedimentation at the sampling point is expressed in g / a. The sampling area is in m2. The area represents the study region, expressed in m². The content of element i in both dry and wet sedimentation is expressed in mg / kg. is the soil settlement correction factor for element i in wet and dry settlement.

[0012] As a method for calculating the input and output flux of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the input flux of fly ash in step S2 is as follows: ; In the formula, The flux of heavy metal element i into the topsoil via fly ash is expressed in kg / a. This represents the total amount of coal burned, expressed in tons per year (t / a). The ratio of fly ash produced by coal combustion, dimensionless; The percentage of fly ash remaining in the topsoil is dimensionless. The content of element i in fly ash is expressed in mg / kg.

[0013] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the comprehensive input flux of agricultural production in step S2 is as follows: ; In the formula, The flux of heavy metal element i into the topsoil via agricultural production, in kg / a; ; The total amount of input for a certain type of agriculture, expressed in tons per year (t / a). The content of element i in a certain agricultural input, in mg / kg.

[0014] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the surface runoff output flux in step S3 is as follows: ; In the formula, Let i be the output flux of element i via surface runoff, in kg / a; The total annual runoff in the study area is expressed in m³. 3 / a; The concentration of element i in surface runoff is expressed in mg / L.

[0015] As a method for calculating the input and output flux of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the output flux of agricultural products sold abroad in step S3 is as follows: ; In the formula, For elements Export flux of agricultural products (kg / a); ; For a certain agricultural product in the research area Annual output, in t / a; For agricultural products in the research area Consumption at the place of origin, in t / a; (This is for the study area to sell agricultural products to external markets) The quantity, in units of t / a; For a certain agricultural product medium elements The average content, in mg / kg.

[0016] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the soil erosion output flux in step S3 is as follows: SE i =S 总 ×E×W i，土壤； In the formula, SE i E represents the output flux of heavy metal element i via soil erosion, in kg / a; E represents the annual soil erosion modulus of the study area, in t / (hm²). 2 •a); W i，土壤 The background concentration of element i in the topsoil is expressed in mg / kg.

[0017] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the formula for calculating the mercury exchange output flux at the soil / atmosphere interface in step S3 is as follows: ; ; In the formula, The density of Hg release flux in surface soil is expressed in ng / m² / h. This represents the light intensity value, measured in W / m². This represents the concentration of Hg in the topsoil, expressed in mg / kg. The value represents the Hg flux from the topsoil of the study area to the atmosphere, expressed in kg / a. The area represents the study region.

[0018] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the method for determining the migration and transformation correction coefficient in step S4 is as follows: k m,i =k pH,i ×k OM,i ×kc lay,i ; In the formula, k m,i k is the comprehensive migration and transformation correction coefficient for heavy metal element i; pH,i The pH correction factor is determined based on the relationship between soil pH and the solubility of element i; k OM,i The organic matter correction factor is determined based on the relationship between soil organic matter content and the complexing ability of element i; kc lay,i This is the clay content correction factor, determined based on the relationship between soil clay content and the adsorption capacity of element i.

[0019] As a method for calculating the input and output fluxes of heavy metals in arable land soil according to the present invention, preferably, the calculation formula for the input-output balance analysis in step S5 is as follows: ; ; ; In the formula, The total amount of input for element i through all input paths, in units of t / a; The total output of element i through all output paths, in t / a; When the value is greater than 0, element i represents net input. When < 0, element i represents net output, in units of t / a. When calculating the output flux of Hg, it should also include... .

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention pioneered the quantitative accounting of agricultural product exports (annual output minus local consumption) as the core output item, accurately distinguishing between the internal circulation of heavy metals within the production area and the output from outside the region. It is particularly suitable for major production areas of specialty agricultural products with high export rates, such as tea, fruits, vegetables, and Chinese medicinal herbs, as well as major grain production areas. The calculation results can truly reflect the actual balance of heavy metals in the regional arable land soil.

[0021] This invention, by comprehensively considering two important agricultural internal input pathways—the return of livestock and poultry manure to the field and the return of straw to the field—as well as soil erosion output pathways, makes up for the deficiencies of existing technologies and fully covers the main input and output processes of heavy metals in arable land soil.

[0022] This invention introduces a dynamic correction coefficient for soil physicochemical properties, taking into account the influence of pH, organic matter content, and clay content on heavy metal migration and transformation, thus reflecting the spatial heterogeneity of fluxes under different soil types. For mercury, a multiple linear regression equation fitted based on measured data from the study area is used, while also considering the influence of various meteorological factors, significantly improving the calculation accuracy of volatile heavy metal output fluxes.

[0023] This invention distinguishes between the consumption of agricultural products at their place of origin and their export, only including heavy metals carried away by exported agricultural products in the output flux, thus avoiding an overestimation of the output flux. Furthermore, it introduces corresponding correction coefficients to address the characteristics of different input and output pathways, making the calculation results more consistent with the actual conditions of the study area.

[0024] This invention, through the calculated flux results and balance analysis, can accurately identify the main input and output pathways of heavy metals in arable soil, assess pollution risks, and provide a scientific basis for formulating targeted pollution prevention and control measures. It is of great significance for ensuring the quality and safety of agricultural products and the health of the ecological environment. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 A schematic diagram illustrating the steps of the method for calculating the input and output fluxes of heavy metals in arable land soil. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1 The present invention provides the following technical solution: a method for calculating the input and output fluxes of heavy metals in arable land soil, the following embodiments are provided. Basic data collection and preprocessing for the S1 study area: Data collected from statistical yearbooks: The total cultivated land area of ​​the study area is 1000 hm². 2 The main soil type is red soil; meteorological data: average annual rainfall of 1500 mm, average annual sunlight intensity of 200 W / m². 2 The average annual temperature is 20℃, and the average annual relative humidity is 80%. Agricultural production data: annual irrigation water volume is 5 million cubic meters. 3 Annual fertilizer application: 2000 t; annual pesticide application: 50 t; annual livestock and poultry manure return to the field: 3000 t; annual straw return to the field: 4000 t; annual plastic film usage: 50 t; annual rice yield: 8000 t (of which 2000 t is consumed at the production site and 6000 t is sold outside the area); coal combustion: 10000 t; fly ash generation rate: 20%; residue rate: 80%; annual surface runoff: 3 million m³. 3 Annual soil erosion modulus 500 t / (hm) 2 •a); Experimental analysis of measured data: Soil physicochemical properties: average pH value 5.5, organic matter content 20 g / kg, clay content 30%; Heavy metal content in various media (taking cadmium (Cd) as an example): Cd content in dry and wet deposition: 0.5 mg / kg; Cd content in fly ash: 1.0 mg / kg; Cd concentration in irrigation water: 0.001 mg / L; Cd content in fertilizer: 0.2 mg / kg; Cd content in pesticides: 0.1 mg / kg; Cd content in livestock and poultry manure: 0.3 mg / kg; Cd content in straw: 0.4 mg / kg; Cd content in plastic film: 0.6 mg / kg; Cd content in edible parts of rice: 0.1 mg / kg; Cd concentration in surface runoff: 0.0005 mg / L; Background Cd content in topsoil: 0.2 mg / kg.

[0028] S2 Multi-Source Heavy Metal Input Flux Calculation: The atmospheric dry and wet deposition, fly ash, and agricultural production input fluxes were calculated separately. Taking cadmium (Cd) as an example, the Cd content in dry and wet deposition is 0.5 mg / kg, and the annual deposition amount is 100 g / hm². 2 The soil settlement correction factor is 0.8, therefore the atmospheric dry and wet settlement input flux is: D cd =(100×10 -3 kg / hm 2 ×1000hm 2 () × 0.5 mg / kg × 0.8 = 0.4 kg / a; The Cd content in fly ash is 1.0 mg / kg, and the bioavailability correction factor is 0.6. Therefore, the fly ash input flux is: C cd =10000t / a×0.2×0.8×1.0mg / kg×0.6=0.96kg / a; In the comprehensive input fluxes for agricultural production, the Cd concentration in irrigation water is 0.001 mg / L, the Cd content in fertilizer is 0.2 mg / kg, the Cd content in pesticides is 0.1 mg / kg, the Cd content in livestock and poultry manure is 0.3 mg / kg, and the Cd content in straw is 0.4 mg / kg. The soil transformation correction coefficients for each pathway are 0.9, 0.7, 0.8, 0.6, and 0.5, respectively. Therefore, the comprehensive input fluxes for agricultural production are: A cd =(500x10 3 m 3 ×0.001mg / L×0.9)+(2000t×0.2mg / kg×0.7)+(50t×0.1mg / kg; The total input flux of Cd is: F in Cd =0.4 + 0.96 + 2.074 = 3.434 kg / a; S3 Calculation of Heavy Metal Output Flux via Multiple Pathways: The output fluxes from surface runoff, agricultural product exports, and soil erosion were calculated separately. Based on experimentally measured Cd concentrations of 0.0005 mg / L in surface runoff and a sediment-bound state correction factor of 0.9, the surface runoff output flux is: RO cd =300x10 3 m 3 x0.0005mg / L x0.9 = 0.135kg / a; According to experimental measurements, the Cd content in the edible portion of rice is 0.1 mg / kg, with an enrichment factor correction value of 1.1. Therefore, the export flux of agricultural products is: AP ca =(8000-2000)tx0.1mg / kgx1.1=0.66kg / a; The background Cd concentration in the soil is 0.2 mg / kg, and the erosion enrichment coefficient is 1.5. Therefore, the soil erosion output flux is: SE cd =1000hm2x500t / (hm2.a)x0.2mg / kgx1.5=150kg / a; The total output flux of Cd is: F cd out =0.135 + 0.66 + 150 = 150.795 kg / a; Dynamic correction of S4 soil physicochemical properties: Based on soil pH of 5.5, organic matter content of 20 g / kg, and clay content of 30%, the comprehensive migration and transformation correction factor for Cd was determined to be 0.8. The corrected total input flux is: F cd,修正 out =150.795 x 0.8 = 120.636 kg / a; S5 Input-Output Balance Analysis and Risk Assessment: The net flux of Cd is: △F cd =2.747 - 120.636 = -117.889 kg / a; The negative net flux indicates that Cd is a net exporter in the farmland soil of the study area. Combined with soil background values, the Cd pollution risk in the farmland soil of this region is assessed as safe.

[0029] The method for calculating the input and output fluxes of heavy metals in arable land soil according to this invention follows a logical process of "data acquisition - flux calculation - dynamic correction - balance analysis - risk assessment". Its core principle is to accurately calculate the net flux of heavy metals by quantifying all major input and output processes of heavy metals in the arable land ecosystem, combined with the influence of soil physicochemical properties on the migration and transformation of heavy metals, thereby assessing the risk of soil pollution. The specific process principle is as follows: Data Acquisition and Preprocessing Stage: This stage forms the foundation of the entire computational method. It involves systematically collecting soil, meteorological, agricultural, industrial, and hydrological data from the study area to provide comprehensive and accurate basic data for subsequent flux calculations. The preprocessing process ensures data standardization and consistency, eliminating the impact of outliers and missing values ​​on the calculation results.

[0030] Multi-source input flux calculation stage: This stage comprehensively quantifies the sources of heavy metals entering arable soil, including atmospheric dry and wet deposition, industrial fly ash, and comprehensive agricultural inputs. Notably, the comprehensive agricultural inputs stage integrates five pathways for the first time: irrigation water, fertilizers, pesticides, livestock manure return to the field, and straw return to the field, covering all major heavy metal input sources in agricultural production processes. The calculation formulas for each input flux incorporate corresponding correction coefficients to reflect the actual proportions and bioavailability of heavy metals entering the soil from different sources.

[0031] Multi-pathway output flux calculation stage: This stage comprehensively quantifies the pathways of heavy metal output from arable land soil, including surface runoff, agricultural product exports, soil erosion, and mercury exchange at the soil-atmosphere interface. The inclusion of soil erosion as an output pathway addresses the limitations of existing technologies in sloping arable land areas; agricultural product export output only considers the export portion, avoiding overestimation of output flux; and mercury exchange output employs a localized multiple linear regression equation, improving the accuracy of volatile heavy metal calculations.

[0032] Dynamic Correction Stage: This stage is one of the core innovations of this invention. By introducing dynamic correction coefficients for soil physicochemical properties, the effects of pH, organic matter content, and clay content on heavy metal migration and transformation are considered. Under different soil types, the solubility, adsorption capacity, and bioavailability of heavy metals vary significantly. The dynamic correction mechanism can reflect this spatial heterogeneity, making the calculation results more consistent with reality.

[0033] Balance Analysis and Risk Assessment Phase: This phase calculates the corrected total input flux and total output flux to obtain the net flux of heavy metals, and analyzes the dynamic balance of heavy metals in arable land soil. Based on the net flux and soil background values, the single-factor pollution index method is used to assess pollution risk and identify the main input and output pathways, providing a scientific basis for developing targeted pollution prevention and control measures.

[0034] Through the above process, this invention achieves comprehensive and accurate calculation of the input and output fluxes of heavy metals in arable land soil, solving the problems of incomplete consideration of input and output pathways, lack of dynamic correction mechanism, and low calculation accuracy of volatile heavy metals in existing technologies, and providing strong technical support for the prevention and control of heavy metal pollution in arable land soil.

[0035] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the input and output fluxes of heavy metals in arable land soil, characterized in that, Includes the following steps: S1. Basic data collection and preprocessing in the study area: Collect soil physicochemical properties data, meteorological data, agricultural production chain data, industrial emission data and hydrological data of cultivated land in the study area, and perform standardized preprocessing. S2. Calculation of multi-source heavy metal input flux: Calculate the atmospheric dry and wet deposition input flux, fly ash input flux, and comprehensive agricultural production input flux, respectively. The comprehensive agricultural production input flux includes irrigation water input flux, fertilizer input flux, pesticide input flux, livestock and poultry manure return to the field input flux, and straw return to the field input flux. S3. Calculation of heavy metal output flux through multiple pathways: Calculate the output flux of surface runoff, output flux of agricultural products sold abroad, and output flux of soil erosion. For mercury, calculate the output flux of mercury exchange at the soil-atmosphere interface. S4. Dynamic Correction of Soil Physicochemical Properties: Based on soil pH, organic matter content, and clay content, determine the migration and transformation correction coefficients for each heavy metal element. Based on experimentally measured soil pH, organic matter content, and clay content, determine the input availability correction coefficients for each heavy metal element. Only all input fluxes obtained in step S2 are corrected. The correction coefficients only reflect the effective proportion of heavy metals entering the soil that can participate in the soil ecosystem cycle and do not affect the output fluxes that have left the soil. S5. Input-output balance analysis and risk assessment: Calculate the corrected total input and output of heavy metals to obtain the net flux, analyze the dynamic balance of heavy metals in arable land soil, and assess the pollution risk based on the net flux and soil background values.

2. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 1, characterized in that: The formula for calculating the atmospheric dry and wet deposition input flux in S2 is as follows: ； In the formula, The flux of a certain heavy metal element i into the topsoil via dry and wet deposition is expressed in kg / a. The total mass of dry and wet sedimentation at the sampling point is expressed in g / a. The sampling area is in m2. The area of ​​the study region is expressed in m². The content of element i in both dry and wet sedimentation is expressed in mg / kg. is the soil settlement correction factor for element i in wet and dry settlement.

3. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 1, characterized in that: The formula for calculating the fly ash input flux in S2 is as follows: ； In the formula, The flux of heavy metal element i into the topsoil via fly ash is expressed in kg / a. This represents the total amount of coal burned, expressed in tons per year (t / a). The ratio of fly ash produced by coal combustion, dimensionless; The percentage of fly ash remaining in the topsoil is dimensionless. The content of element i in fly ash is expressed in mg / kg.

4. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 1, characterized in that: The formula for calculating the comprehensive input flux of agricultural production in S2 is as follows: ； In the formula, The flux of heavy metal element i into the topsoil via agricultural production, in kg / a; ; The total amount of input for a certain type of agriculture, expressed in tons per year (t / a). The content of element i in a certain agricultural input, in mg / kg.

5. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 1, characterized in that: The formula for calculating the surface runoff output flux in S3 is as follows: ； In the formula, Let i be the output flux of element i via surface runoff, in kg / a; The total annual runoff in the study area is expressed in m³. 3 / a; The concentration of element i in surface runoff is expressed in mg / L.

6. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 5, characterized in that: The formula for calculating the export throughput of agricultural products in S3 is as follows: ； In the formula, For elements Export flux of agricultural products (kg / a); ; For a certain agricultural product in the research area Annual output, in t / a; For agricultural products in the research area Consumption at the place of origin, in t / a; (This is for the study area to sell agricultural products to external markets) The quantity, in units of t / a; For a certain agricultural product medium elements The average content, in mg / kg.

7. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 3, characterized in that: The formula for calculating the soil erosion output flux in S3 is as follows: SE i =S 总 ×E×W i，土壤； In the formula, SE i E represents the output flux of heavy metal element i via soil erosion, in kg / a; E represents the annual soil erosion modulus of the study area, in t / (hm²). 2 •a); W i，土壤 The background concentration of element i in the topsoil is expressed in mg / kg.

8. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 3, characterized in that: The formula for calculating the mercury exchange flux at the soil / atmosphere interface in S3 is as follows: ； ; In the formula, The density of Hg release flux in surface soil is expressed in ng / m² / h. This represents the light intensity value, measured in W / m². This represents the concentration of Hg in the topsoil, expressed in mg / kg. The value represents the Hg flux from the topsoil of the study area to the atmosphere, expressed in kg / a. The area represents the study region.

9. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 3, characterized in that: The method for determining the migration and transformation correction coefficient in S4 is as follows: k m,i =k pH,i ×k OM,i ×kc lay,i ; In the formula, k m,i k is the comprehensive migration and transformation correction coefficient for heavy metal element i; pH,i The pH correction factor is determined based on the relationship between soil pH and the solubility of element i; k OM,i The organic matter correction factor is determined based on the relationship between soil organic matter content and the complexing ability of element i; kc lay,i This is the clay content correction factor, determined based on the relationship between soil clay content and the adsorption capacity of element i.

10. The method for calculating the input and output fluxes of heavy metals in arable land soil according to claim 3, characterized in that: The calculation formula for the input-output balance analysis in S5 is as follows: ; ; ; In the formula, The total input of element i through all input paths, in units of t / a; The total output of element i through all output paths, in t / a; When the value is greater than 0, element i represents net input. When <0, element i represents net output, in units of t / a. When calculating the output flux of Hg, it should also include... .

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