A heavy metal traceability investigation and influence evaluation method and system based on coupling mechanism of pollutant multi-path migration process

Abstract

This invention provides a method and system for heavy metal source tracing and impact assessment based on the coupling mechanism of multi-pathway migration processes of pollutants. The system includes: data collection and monitoring surveys, pollutant source tracing analysis, heavy metal occurrence and release risk analysis, migration and transformation model construction and parameter experiments, simulation and impact assessment. It adopts a closed-loop technical route of "field investigation-monitoring-source tracing-simulation-assessment," constructing a multi-module migration and transformation model coupling hydrodynamics, sediment transport, convection-diffusion transport, and sediment-water interface exchange, and calibrating key parameters through indoor experiments. This invention can achieve accurate identification of heavy metal pollution sources and refined simulation of migration processes, supporting forward risk extrapolation and reverse control threshold calculation, providing systematic technical support for watershed water environment governance and protection.

Description

Technical Field

[0001] This invention relates to the field of environmental science research, specifically a method and system for tracing the source and assessing the impact of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants. Background Technology

[0002] With the acceleration of industrialization, urbanization, and agricultural intensification, heavy metals enter the environment in large quantities through natural and human activities, accumulating in soil and entering water bodies through rainfall runoff, posing a threat to the ecological environment and human health. The migration and transformation of heavy metals is a complex process involving multiple physical, chemical, and biological mechanisms. In water bodies, heavy metals mainly exist in dissolved, suspended, and sedimentary states, migrating through convection and diffusion, and undergoing speciation through chemical reactions such as adsorption, desorption, redox reactions, and complexation precipitation, as well as biological processes such as microbial metabolism and bioaccumulation. River sediments, as important reservoirs of heavy metals, undergo secondary migration through resuspension, diffusion, and sedimentation due to changes in environmental conditions. The adsorption and desorption of heavy metals by sediment is a crucial link in this process, not only affecting the distribution of heavy metals in water bodies but also significantly impacting their ecological risks.

[0003] Currently, most heavy metal pollution models only consider the macroscopic migration and diffusion process of heavy metals with water flow, without taking into account the influence of factors such as sediment movement and sediment release. They do not truly reflect the actual migration process of heavy metals in water bodies. There is an urgent need to further strengthen the mechanism research of each link in the heavy metal transport and transformation process by coupling field monitoring, indoor experiments and model simulation technologies. In this way, a dedicated model for river heavy metal migration and transformation that comprehensively considers various pollution sources and couples multi-path migration processes can be developed to provide technical support for heavy metal source tracing and impact assessment.

[0004] To address this, this invention proposes a method and system for heavy metal source tracing and impact assessment based on the coupling mechanism of multi-pathway migration processes of pollutants. It adopts a technical route of "field investigation - on-site sampling and monitoring - source tracing analysis - simulation and prediction - impact assessment" to conduct research on heavy metal source tracing and impact assessment methods, providing technical support for water environment governance and protection. This invention has a clear concept, strong operability, and high practicality. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies in simulating the migration and diffusion processes of heavy metals with water flow. It proposes a method and system for heavy metal source tracing and impact assessment based on the coupling mechanism of multi-pathway migration processes of pollutants. This invention can strengthen the mechanistic expression of each stage in the heavy metal migration and transformation process, further enriching the methodological system of heavy metal source tracing and impact analysis, and providing important support for watershed water environment governance and protection.

[0006] A method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration of pollutants includes the following steps:

[0007] S1: Data collection and monitoring survey: Collect basic data of the target watershed, set up monitoring sections and stations, and obtain multiple rounds of hydrological, water quality and sediment monitoring data. The basic data includes the distribution of pollution sources, hydrological characteristics and current land use.

[0008] S2: Pollutant source analysis: Based on the monitoring data obtained in step S1, analyze the changes in heavy metal concentration in the water along the process, calculate the heavy metal flux at key sections, and combine the pollution source distribution in the basic data to comprehensively determine the composition of heavy metal pollution sources.

[0009] S3: Speciation and Release Risk Analysis: Detect the content of different occurrence speciations of heavy metals in water bodies and sediments, analyze their spatiotemporal distribution characteristics, and analyze the spatiotemporal distribution characteristics based on the monitoring data in step S1. Use the geoaccumulation index method to assess the heavy metal pollution level and release risk of sediments.

[0010] S4: Model Construction and Parameter Experiment: Based on the hydrological and water quality data in step S1 and the morphological analysis results in step S3, a migration and transformation model is constructed that couples the hydrodynamic module, sediment transport module, heavy metal convection-diffusion transport module, and sediment-water interface exchange module; the key parameters of dissolved-particulate partition coefficient and adsorption-desorption coefficient are determined through indoor experiments, and the model is calibrated to obtain the calibrated migration and transformation model;

[0011] S5: Simulation and Impact Assessment: Using the migration and transformation model calibrated in step S4, forward simulations are conducted under different operating conditions to analyze the concentration variation patterns and peak times of heavy metal migration and assess the risks to downstream water quality. Simultaneously, with the target section's water quality compliance as a constraint, the concentration control thresholds for each major section along the route are calculated in reverse, and corresponding pollution control optimization suggestions are proposed.

[0012] Furthermore, in step S4, the constructed migration and transformation model simulates water flow by coupling a hydrodynamic module, simulates sediment movement as a carrier of heavy metals by coupling a sediment transport module, simulates the transport of dissolved and particulate heavy metals by coupling a heavy metal convection-diffusion transport module, and simulates the exchange process of heavy metals between water and sediment by coupling a sediment-water interface exchange module.

[0013] Furthermore, in the sediment-water interface exchange module, the diffusion flux of dissolved heavy metals from sediment to water body... Calculated using the following formula:

[0014] ;

[0015] In the formula, It is the flux of dissolved heavy metals diffusing from sediments into water bodies, measured in μg / m² / s; It represents the concentration of heavy metals in the pore water of sediments, expressed in μg / m³. It is the concentration of dissolved heavy metals in water, expressed in μg / m³. It is the diffusion coefficient of dissolved heavy metals in sediments, with units of m² / s;

[0016] Sedimentation flux of particulate heavy metals Calculated using the following formula:

[0017] ;

[0018] Resuspension flux of particulate heavy metals Calculated using the following formula:

[0019] ;

[0020] In the formula, It is the sedimentation flux of particulate heavy metals, with units of μg / m² / s; It is the sediment settling velocity, measured in m / s; It represents the concentration of particulate heavy metals in water, expressed in μg / m³. It is the resuspension flux of particulate heavy metals, expressed in μg / m² / s; It is the sediment resuspension rate, measured in kg / m² / s; It is the concentration of heavy metals per unit mass of sediment, expressed in μg / kg.

[0021] Furthermore, the forward simulation in step S5 specifically includes setting different hydrodynamic conditions, different pollution input concentrations, and different pollution control measures to simulate the entire migration and diffusion process of heavy metals in the watershed, outputting the concentration time process at each cross section along the river, and analyzing the concentration peak and the duration of exceeding the standard to assess the risk.

[0022] Furthermore, the forward simulation in step S5 specifically includes setting different hydrodynamic conditions, different pollution input concentrations, and different pollution control measures to simulate the entire migration and diffusion process of heavy metals in the watershed, outputting the concentration time process at each cross section along the river, and analyzing the concentration peak and the duration of exceeding the standard to assess the risk.

[0023] A heavy metal source tracing and impact assessment system based on the coupling mechanism of multi-pathway migration processes of pollutants includes:

[0024] The data acquisition and monitoring unit is used to collect basic data of the target watershed, set up monitoring sections and stations, and acquire multiple rounds of hydrological, water quality and sediment monitoring data. The basic data includes the distribution of pollution sources, hydrological characteristics and current land use.

[0025] The source analysis unit is used to analyze the changes in heavy metal concentration in water along the course of the river based on the acquired monitoring data, calculate the heavy metal flux at key sections, and comprehensively determine the composition of heavy metal pollution sources by combining the pollution source distribution in the basic data.

[0026] The morphological analysis and risk assessment unit detects the content of different occurrence forms of heavy metals in water bodies and sediments, analyzes their spatiotemporal distribution characteristics, and analyzes the spatiotemporal distribution characteristics based on the monitoring data in step S1. The geoaccumulation index method is used to assess the heavy metal pollution level and release risk of sediments.

[0027] The migration and transformation model construction and experimental unit is used to construct a migration and transformation model based on hydrological and water quality data from monitoring data and the morphological analysis results from the morphological analysis and risk assessment unit, which couples a hydrodynamic module, a sediment transport module, a heavy metal convection-diffusion transport module, and a sediment-water interface exchange module. The model is calibrated by measuring key parameters such as the dissolved-particulate partition coefficient and the adsorption-desorption coefficient through indoor experiments to obtain the calibrated migration and transformation model.

[0028] The simulation and comprehensive evaluation unit is used to perform forward simulations under different operating conditions using a calibrated migration and transformation model, analyze the concentration change patterns and peak times of heavy metal migration, and assess the risks to downstream water quality. At the same time, with the target section water quality compliance as a constraint, it reverse-engineers the concentration control thresholds for each major section along the route and proposes corresponding pollution control optimization suggestions.

[0029] Furthermore, the core mechanism of the migration and transformation model constructed in the experimental unit includes: considering the distribution relationship between dissolved and particulate heavy metals, driving the migration process through a hydrodynamic module, describing the carrier movement of heavy metals through a sediment transport module, simulating its transport in water through a heavy metal convection-diffusion transport module, and characterizing the exchange process of heavy metals between sediments and water through a sediment-water interface exchange module.

[0030] Furthermore, the core mechanism of the migration and transformation model constructed in the experimental unit includes: considering the distribution relationship between dissolved and particulate heavy metals, driving the migration process through a hydrodynamic module, describing the carrier movement of heavy metals through a sediment transport module, simulating its transport in water through a heavy metal convection-diffusion transport module, and characterizing the exchange process of heavy metals between sediments and water through a sediment-water interface exchange module.

[0031] Furthermore, when the simulation and comprehensive evaluation unit conducts forward simulation, the set operating conditions include: different hydrodynamic conditions represented by flood processes of different frequencies, different pollution concentrations based on actual measurements or assumptions, and operating conditions of existing or failed pollution treatment measures.

[0032] The present invention has the following beneficial effects:

[0033] 1. Overcoming the shortcomings of existing models: In view of the inadequacy of existing heavy metal pollution models that only consider macroscopic migration and diffusion, this invention couples multiple modules such as hydrodynamics, sediment transport, and sediment-water interface exchange to realistically reflect the processes of heavy metal form transformation and secondary migration, thereby improving the accuracy of simulation.

[0034] 2. Construct a closed-loop technology system: Adopt a closed-loop route of "on-site visits - monitoring - source tracing - simulation - assessment", integrate data collection, source tracing analysis, risk assessment, model simulation and other links to provide systematic support for the source tracing and impact assessment of heavy metal pollution.

[0035] 3. Achieve refined management and control: By measuring key parameters (such as distribution coefficient and adsorption-desorption coefficient) through indoor experiments and combining simulations under different operating conditions, it is possible to both positively assess water quality risks and reversely calculate concentration control thresholds, providing quantitative basis for measures such as optimizing dosing points.

[0036] 4. Enhance practical value: Enrich the system of methods for tracing and assessing heavy metals, which can be directly applied to scenarios such as watershed water environment management and pollution prevention and control planning, and is of great significance to ensuring ecological and environmental security. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the special model for antimony metal migration and transformation of the present invention.

[0038] Figure 2 This is a flowchart of a method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration of pollutants, according to an embodiment of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0040] Example: Taking antimony pollution as an example, this invention demonstrates a method for heavy metal source tracing and impact assessment based on the coupling mechanism of multi-pathway migration processes of pollutants, such as... Figure 2 As shown, the method includes the following steps:

[0041] (1) Collect data on antimony mine tailings ponds and hydrological and water quality data within the survey area.

[0042] Information was collected on the location, type, scale, and mining history of antimony tailings ponds, mining areas under construction / pending / suspended operations, and abandoned mining areas within the watershed. Data on the distribution of forest land, farmland, mining areas, and human production and living areas within the watershed was also collected, including information on the area, geographical location, spatial distribution pattern, and current land use of each region. Hydrological and water quality monitoring was conducted at cross-sections under different water inflow conditions. Monitoring results were collected during the survey period. The monitored water quality indicators included nine items: water temperature, pH value, dissolved oxygen, conductivity, dissolved antimony, total antimony, iron, manganese, and sulfate. Hydrological indicators included water level, flow rate, flow velocity distribution, average suspended sediment content and particle size distribution at the cross-section, and large cross-section data. The layout of hydrological and water quality monitoring cross-sections followed these principles:

[0043] Objective-oriented principle: With the core objectives of accurately grasping the antimony pollution status of the basin and precisely assessing the effectiveness of pollution prevention and control measures, we will scientifically plan the layout of monitoring sections to ensure that the monitoring data can provide effective support for antimony pollution source tracing, migration and transformation law research, and water quality risk management.

[0044] Systematic principle: Taking into account the distribution of the water system, the inflow of tributaries, the location of pollution sources and hydrological characteristics, background sections are set up, and monitoring sections are set up at key locations such as the upstream of the inflow of each tributary and the upstream of the dosing point to achieve coverage of key areas of the watershed and to reflect the distribution characteristics of antimony pollution in different areas relatively completely.

[0045] The principle of highlighting key points is to set up cross-sections upstream of key nodes in the migration and transformation of pollutants, such as dosing points and integrated treatment stations, and downstream after the reaction is complete, to focus on monitoring changes in water quality before and after dosing treatment and to accurately control the antimony pollution treatment effect; at the same time, attention should be paid to the impact of tributary inflows on the pollution of the main stream, and cross-sections should be set up upstream of the tributary inflows to understand the pollution status of the tributary water.

[0046] The principle of combining time and space: In terms of space, monitoring sections are rationally laid out to ensure effective monitoring of different locations in the basin; in terms of time, the number of measurements is scientifically and rationally arranged in combination with different hydrological periods such as high water season, normal water season, and low water season, as well as special circumstances such as sudden pollution events, to ensure the representativeness of water quality and hydrological data and reflect the changing pattern of antimony pollution over time.

[0047] (2) Antimony pollution source tracing analysis

[0048] The monitoring results of various cross-sections were comprehensively analyzed, with a focus on the variation of antimony concentration in the water along the river. Based on synchronous monitoring data of water quality and quantity, the antimony flux at relevant cross-sections was calculated. The composition of antimony pollution sources was analyzed by integrating the survey results of water bodies, sediments, soils, and mining areas within the basin.

[0049] (3) Detection of antimony metal occurrence modes and spatiotemporal distribution analysis

[0050] 1) Antimony metal speciation detection

[0051] Antimony metal speciation detection in water: Antimony metal speciation in water is generally divided into dissolved and particulate forms, and the total amount is the sum of the two. Dissolved antimony is determined by filtering the collected water sample through a filter membrane and then measuring it according to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ 700-2014). The content of particulate antimony is calculated using the differential method (total amount minus dissolved amount). The total antimony content is determined by sample pretreatment according to the standard "Digestion Method for Total Metals in Water by Microwave Digestion" (HJ 678-2013), and then analyzed using the instrument according to the relevant technical requirements of "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ 700-2014).

[0052] Antimony metal speciation in sediments: Heavy metal speciation in sediments can generally be classified into five types: exchangeable, carbonate-bound, iron-manganese oxide-bound, organic matter and sulfide-bound, and residual. Based on the results of the first sediment monitoring study, samples from representative sites were selected for analysis of different antimony speciations. The Tessier method was used to extract different antimony speciations stepwise, and the extraction conditions are shown in Table 1. After extraction, the samples were filtered and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) for the determination of 65 elements in water (HJ 700-2014). Principal component analysis was then used to analyze the main antimony speciations in the sediments.

[0053] Table 1. Steps of the Tessier sequential extraction method

[0054]

[0055] 2) Analysis of the occurrence modes of antimony metal

[0056] Based on monitoring data of antimony in water and sediments, the distribution patterns of dissolved and particulate (suspended) antimony in water along the course of the river were analyzed, and the main occurrence forms of antimony in sediments at representative points along the course of the river were analyzed.

[0057] 3) Spatiotemporal distribution analysis of antimony metal

[0058] The mean and measured values ​​of antimony metal in the surveyed river section were calculated, along with the standard deviation and coefficient of variation (Cv), to analyze the spatial variability of heavy metals in sediments. Cv ≤ 0.2 indicates low variability, 0.2 < Cv ≤ 0.5 indicates moderate variability, 0.5 < Cv ≤ 1.0 indicates high variability, and Cv > 1.0 indicates extremely high variability. The spatiotemporal distribution characteristics of antimony in water bodies, sediments, and watershed surface soil were analyzed, and a spatiotemporal distribution map of antimony metal in the watershed was drawn.

[0059] (4) Sediment pollution level assessment and antimony release risk analysis

[0060] The geoaccumulation index method was used to conduct a risk assessment of heavy metals in sediments, analyze their pollution and hazard levels, and evaluate their ecological risks. The formula for the geoaccumulation index is:

[0061]

[0062] In the formula, C n The concentration of element n in the sample; BE n The concentration represents the geochemical background concentration; k is a constant, and considering that diagenesis may cause variations in the background value, k is generally set to 1.5. The geoaccumulation index is divided into 6 levels (Table 2), with levels 0 to 6 representing pollution levels from none to extremely high. Different levels represent different degrees of heavy metal pollution.

[0063] Table 2. Geological Accumulation Index Pollution Assessment Standards

[0064]

[0065] (5) Research and experiment on antimony metal migration and transformation model

[0066] 1) Model Building

[0067] Based on in-situ monitoring data of antimony metal in the watershed, a dedicated model for antimony metal migration and transformation was further developed, building upon the river hydrodynamic-water quality model. The model primarily considers the migration and transformation processes of antimony metal, including convection, diffusion, sedimentation, resuspension, and adsorption / desorption, to simulate its migration, diffusion, and transformation behavior in water bodies and sediments. This enables refined simulation and prediction of antimony metal migration and transformation under different hydrological and environmental conditions in the watershed, providing a scientific quantitative tool for antimony metal pollution prevention and risk assessment. The model includes a hydrodynamic module, a sediment transport module, an antimony metal convection-diffusion transport module, and a sediment-water interface exchange module. The hydrodynamic and sediment transport modules provide the basic framework of the model. Building upon the first two modules, the antimony metal convection-diffusion transport module and the sediment-water interface exchange module consider the convection and diffusion processes of antimony metal as well as its exchange with sediments, simulating the migration and transformation processes of antimony metal in water bodies.

[0068] Heavy metals are highly difficult to biodegrade and mainly manifest as migration and transformation in water bodies. For example, heavy metal compounds existing in dissolved states in rivers can react and transform into suspended solids. Under certain conditions, these suspended solids can settle and enter the sediment. Heavy metals in the sediment can then be resuspended, becoming suspended solids again. Heavy metals in both suspended solids and sediment can then transform into water-soluble forms, undergoing repeated transformations and migrating with the water body. The main factors influencing the migration and transformation of heavy metal pollution are: ① convection and diffusion; ② adsorption of dissolved metals by suspended solids and adsorption of dissolved heavy metals by sediment; ③ desorption of heavy metal concentrations in sediment; ④ sedimentation and resuspension of suspended solids; ⑤ source-sink effects. (See model principle for details.) Figure 1 Model building involves the following steps:

[0069] ① Computational grid generation. The computational boundary of the two-dimensional model simulation range is delineated on the remote sensing image, the computational region is divided, and a body-fitted computational grid is generated.

[0070] ②Topographic processing and interpolation. For the studied river section, the effective representation capability of DEM data on underwater topography under exposed river conditions is fully utilized. A 5m resolution DEM image acquired during the dry season is selected as an auxiliary base map. Based on the actual measured cross-section topographic monitoring data to be deployed, after eliminating elevation deviation through cross-correction, the basic topography is generated by Kriging interpolation method in combination with the river direction.

[0071] ③ Boundary condition setting. The inflow boundary is the process of water flow and antimony metal concentration in the upstream of the basin and tributaries (sub-ditches), and is set according to the working conditions of each condition; the outflow hydrological boundary is set according to the basin outlet, and the outflow water quality boundary adopts the free outflow condition, that is, no additional constraints are imposed on the antimony metal concentration, and its concentration is dynamically determined by internal calculation of the model.

[0072] ④ Initial conditions settings. The initial water level value is set according to the measured data for each zone. The initial water quality value can be determined by zone based on the distribution values ​​of various pollutant indicators in the simulated area, or a uniform value can be taken for the calculation area.

[0073] ⑤ Model Calibration and Validation. The model parameters were calibrated by combining hydrological data along the watershed, on-site monitoring results of antimony pollutants, and indoor experimental results. Key model parameters included roughness, horizontal momentum diffusion coefficient, heavy metal adsorption / desorption coefficient, sediment release coefficient, and dissolved / particulate distribution coefficient. The hydrodynamic parameters (roughness, horizontal momentum diffusion coefficient, etc.) were calibrated primarily based on daily measured flow data from key hydrological stations, with the relative error between the simulated flow and measured values ​​controlled within 10% after calibration. Antimony-related parameters (metal adsorption / desorption coefficient, sediment release coefficient, dissolved / particulate distribution coefficient, etc.) were set with reference to the results of planned indoor experiments and calibrated using on-site monitoring data under different inflow scenarios. The relative error between the simulated and measured antimony concentration results was controlled within 30%.

[0074] The principles of heavy metal speciation and model modules are as follows:

[0075] 1) Distribution of heavy metal speciation

[0076] Heavy metals in water exist in two forms: dissolved and particulate (adsorbed onto sediment, etc.). These different forms undergo different physical, chemical, and biological changes. For example, dissolved heavy metals are more likely to participate in redox reactions, while sedimentation occurs only in the particulate form. The amounts of these two forms can be described by the "partition coefficient":

[0077]

[0078]

[0079]

[0080] In the formula, This represents the total concentration of heavy metals. This refers to the concentration of dissolved heavy metals. This represents the concentration of particulate heavy metals, expressed in μg / m³. and The coefficients between the dissolved state and the particulate state and the total concentration, respectively, can be expressed as:

[0081] , ,

[0082] In the formula, is the distribution coefficient, in m³ / g; m is the suspended particulate concentration, in g / m³.

[0083] 2) Hydrodynamic module

[0084] Hydrodynamic processes are the primary driving force behind heavy metal migration. The hydrodynamics module calculates hydrodynamic parameters in the water body, including flow velocity, flow rate, and water level, by solving two-dimensional shallow water equations, simulating the migration path and diffusion rate of heavy metals with the water flow. The two-dimensional shallow water equations are a set of partial differential equations used to describe the flow of water. Their basic form is:

[0085]

[0086] in: , , ,

[0087]

[0088] In the formula, h is the water depth, in meters (m); u and These are the velocity components of the water flow in the x and y directions, respectively, in m / s; g is the acceleration due to gravity, taken as 9.81 m / s². 2 ; This is the density of water, measured in kg / m³. , = These are the bed floor slope terms in the x and y directions, respectively. The elevation is the base elevation, in meters (m). , Let be the friction gradients in the x and y directions, respectively, and n be the Manning roughness coefficient. The equation does not consider the effects of Coriolis force and wind force.

[0089] 3) Sediment transport module

[0090] Heavy metals such as antimony often adhere to the surface of sediment particles; therefore, sediment movement significantly influences the migration of heavy metals. The sediment transport module uses sediment transport equations to describe the settling, resuspension, and transport processes of sediment particles in water bodies. Its basic form is:

[0091]

[0092] In the formula, This is the sediment concentration, expressed in g / m³. and v are the velocity components of the water flow in the x and y directions, respectively, with units of m / s; , This is the sediment diffusion coefficient, expressed in square meters per second (m² / s). It is a source-sink term, which is a comprehensive term including processes such as sediment deposition and resuspension, and the unit is g / m³ / s.

[0093] 4) Heavy metal convection-diffusion transport module

[0094] According to the theory of pollutant transport and mass transfer, the convection and diffusion characteristics of both forms of heavy metals in water bodies are the same; that is, the convective velocity of particulate and dissolved heavy metals is equal to the velocity of water particles at their respective spatial points, and turbulent diffusion and dispersion satisfy Fick's diffusion law. The difference lies in that particulate heavy metals migrate between the aqueous phase and sediments due to sediment settling and bed erosion. The convection-diffusion transport equations for dissolved and particulate heavy metals can be expressed as follows:

[0095]

[0096]

[0097] In the formula, The concentration in the dissolved state. The concentration is expressed as μg / m³, and u and v are the velocity components of the water flow in the x and y directions, respectively, in m / s. and These are the diffusion coefficients in the x and y directions, respectively, in m. 2 / s. The unit is μg / m³ / s, which represents the amount of particulate heavy metals released from sediments into water bodies per unit time under high hydrodynamic conditions (such as floods, increased turbulence, etc.).

[0098] 5) Sediment-water interface exchange module

[0099] The sediment-water interface exchange module simulates the heavy metal exchange process between sediments and water, describing the sedimentation of particulate heavy metals from overlying water into sediments and the release of heavy metals from sediments. This process is closely related to the resuspension and sedimentation of sediments.

[0100] The diffusion flux of dissolved heavy metals can be expressed as:

[0101]

[0102] In the formula, It is the flux of dissolved heavy metals diffusing from sediments into water bodies, measured in μg / m² / s; It represents the concentration of heavy metals in the pore water of sediments, expressed in μg / m³. It is the concentration of dissolved heavy metals in water, expressed in μg / m³. It is the diffusion coefficient of dissolved heavy metals in sediments, with units of m² / s.

[0103] Particulate heavy metal exchange can be expressed as sedimentation flux and resuspension flux, where:

[0104] Settlement flux:

[0105] Resuspension flux:

[0106] In the formula: It is the sedimentation flux of particulate heavy metals, with units of μg / m² / s; It is the sediment settling velocity, measured in m / s; It represents the concentration of particulate heavy metals in water, expressed in μg / m³. It is the resuspension flux of particulate heavy metals, expressed in μg / m² / s; It is the sediment resuspension rate, measured in kg / m² / s; It is the concentration of heavy metals per unit mass of sediment, expressed in μg / kg.

[0107] 2) Indoor simulation experiment

[0108] ① Determination of the partition coefficient between dissolved and particulate states

[0109] Based on the heavy metal concentrations and distances from the dosing point of each sediment and water sample collected in the first sampling, five representative sediment samples with different heavy metal concentrations and capable of reflecting the effects of flocculants were selected for simulation experiments. Through single-factor experiments, three hydraulic disturbance conditions and three heavy metal concentration conditions were set up to investigate the effects of different hydraulic conditions and initial concentrations on the dissolved-particulate partition coefficient (Kd) of heavy metals.

[0110] ② Determination of sediment-heavy metal adsorption-desorption coefficient

[0111] Using five representative sediments identical to those used in the partition coefficient simulation experiment, the effects of equilibrium point concentration, adsorption rate, sediment type, and heavy metal occurrence form on heavy metal adsorption and desorption were clarified, and sediment-heavy metal adsorption-desorption experiments were conducted.

[0112] ③ Heavy metal release test of sediments

[0113] The risk of heavy metal release was studied using a flume experiment. Based on the heavy metal occurrence patterns in water and sediment at various sampling points during different water periods, a key cross section was selected for simulation experiments. The sediment-water interface at the key cross section was the main research object to simulate the heavy metal release characteristics under three different hydraulic conditions and assess its release risk.

[0114] (6) Simulation and Impact Assessment

[0115] Based on the developed and constructed special model for antimony metal migration and transformation, different antimony pollution accident scenarios are set up to carry out positive risk condition simulation and reverse disposal suggestion calculation.

[0116] The migration and diffusion processes of heavy metals such as antimony under representative, adverse, and extreme operating conditions are simulated through forward modeling. This includes different hydrodynamic conditions, different pollution conditions, existing dosing conditions, and adverse risk conditions such as dosing point failure. The study analyzes the changes in antimony concentration at major cross-sections along the watershed, the time of peak antimony concentration, and the time it takes for antimony concentration to drop below the standard value, thereby assessing water quality risks.

[0117] In reverse engineering, considering various adverse risk conditions, and based on the requirements of surface water environmental quality standards, the control concentration limit is set at 5.0 μg / L, which is the standard limit for antimony concentration in surface water sources as stipulated in the "Surface Water Environmental Quality Standard" (GB 3838—2002). The control threshold for antimony concentration at each major section along the river is calculated, and suggestions for optimizing antimony pollution control measures at the dosing points are proposed.

[0118] This invention also provides a system for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration of pollutants, comprising:

[0119] The data acquisition and monitoring unit is used to collect basic data of the target watershed, set up monitoring sections and stations, and acquire multiple rounds of hydrological, water quality and sediment monitoring data. The basic data includes the distribution of pollution sources, hydrological characteristics and current land use.

[0120] The source analysis unit is used to analyze the changes in heavy metal concentration in water along the course of the river based on the acquired monitoring data, calculate the heavy metal flux at key sections, and comprehensively determine the composition of heavy metal pollution sources by combining the pollution source distribution in the basic data.

[0121] The morphological analysis and risk assessment unit detects the content of different occurrence forms of heavy metals in water bodies and sediments, analyzes their spatiotemporal distribution characteristics, and uses the geoaccumulation index method to assess the heavy metal pollution level and release risk of sediments based on the analysis of spatiotemporal distribution characteristics.

[0122] The migration and transformation model construction and experimental unit is used to construct a migration and transformation model based on hydrological and water quality data from monitoring data and the morphological analysis results from the morphological analysis and risk assessment unit, which couples a hydrodynamic module, a sediment transport module, a heavy metal convection-diffusion transport module, and a sediment-water interface exchange module. The model is calibrated by measuring key parameters such as the dissolved-particulate partition coefficient and the adsorption-desorption coefficient through indoor experiments to obtain the calibrated migration and transformation model.

[0123] The simulation and comprehensive evaluation unit is used to perform forward simulations under different operating conditions using a calibrated migration and transformation model, analyze the concentration change patterns and peak times of heavy metal migration, and assess the risks to downstream water quality. At the same time, with the target section water quality compliance as a constraint, it reverse-engineers the concentration control thresholds for each major section along the route and proposes corresponding pollution control optimization suggestions.

[0124] This invention has the following features and effects:

[0125] 1. More complete model mechanism: By coupling multiple modules such as hydrodynamics, sediment transport, and sediment-water interface exchange, it truly reflects the key processes such as the transformation of heavy metals, adsorption-desorption, and secondary release, making up for the shortcomings of existing models that only consider macroscopic migration.

[0126] 2. Closed-loop technology system: Integrating the entire process of "on-site investigation - monitoring - source tracing - simulation - assessment" to achieve systematic support from pollution identification to control recommendations, thereby improving the operability and practicality of the methods.

[0127] 3. Scientific parameter calibration: Key parameters such as partition coefficient and adsorption-desorption coefficient are measured through indoor experiments, and the model is calibrated in combination with field data to improve the accuracy and reliability of the simulation.

[0128] 4. Integrated assessment and control: It can both positively simulate the migration patterns and risks of heavy metals under different working conditions, and reversely deduce the concentration control thresholds of each section, providing quantitative basis for governance measures such as source control and process interception.

[0129] 5. Clear application orientation: The method can be directly applied to the source tracing, risk assessment and governance planning of heavy metal pollution in watersheds, and has important practical value for water environment protection and ecological security.

[0130] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants, characterized in that, Includes the following steps: S1: Data collection and monitoring survey: Collect basic data of the target watershed, set up monitoring sections and stations, and obtain multiple rounds of hydrological, water quality and sediment monitoring data. The basic data includes the distribution of pollution sources, hydrological characteristics and current land use. S2: Pollutant source analysis: Based on the monitoring data obtained in step S1, analyze the changes in heavy metal concentration in the water along the process, calculate the heavy metal flux at key sections, and combine the pollution source distribution in the basic data to comprehensively determine the composition of heavy metal pollution sources. S3: Speciation and Release Risk Analysis: Detect the content of different occurrence speciations of heavy metals in water bodies and sediments, analyze their spatiotemporal distribution characteristics, and analyze the spatiotemporal distribution characteristics based on the monitoring data in step S1. Use the geoaccumulation index method to assess the heavy metal pollution level and release risk of sediments. S4: Model Construction and Parameter Experiment: Based on the hydrological and water quality data in step S1 and the morphological analysis results in step S3, a migration and transformation model is constructed that couples the hydrodynamic module, sediment transport module, heavy metal convection-diffusion transport module, and sediment-water interface exchange module; the key parameters of dissolved-particulate partition coefficient and adsorption-desorption coefficient are determined through indoor experiments, and the model is calibrated to obtain the calibrated migration and transformation model; S5: Simulation and Impact Assessment: Using the migration and transformation model calibrated in step S4, forward simulations are conducted under different operating conditions to analyze the concentration variation patterns and peak times of heavy metal migration and assess the risks to downstream water quality. Simultaneously, with the target section's water quality compliance as a constraint, the concentration control thresholds for each major section along the route are calculated in reverse, and corresponding pollution control optimization suggestions are proposed.

2. The method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants as described in claim 1, characterized in that: In step S4, the constructed migration and transformation model simulates water flow by coupling a hydrodynamic module, simulates sediment movement as a carrier of heavy metals by coupling a sediment transport module, simulates the transport of dissolved and particulate heavy metals by coupling a heavy metal convection-diffusion transport module, and simulates the exchange process of heavy metals between water and sediment by coupling a sediment-water interface exchange module.

3. The method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants as described in claim 2, characterized in that: In the sediment-water interface exchange module, the diffusion flux of dissolved heavy metals from sediment to water body Calculated using the following formula: ； In the formula, It is the flux of dissolved heavy metals diffusing from sediments into water bodies, measured in μg / m² / s; It represents the concentration of heavy metals in the pore water of sediments, expressed in μg / m³. It is the concentration of dissolved heavy metals in water, expressed in μg / m³. It is the diffusion coefficient of dissolved heavy metals in sediments, with units of m² / s; Sedimentation flux of particulate heavy metals Calculated using the following formula: ； Resuspension flux of particulate heavy metals Calculated using the following formula: ； In the formula, It is the sedimentation flux of particulate heavy metals, with units of μg / m² / s; It is the sediment settling velocity, measured in m / s; It represents the concentration of particulate heavy metals in water, expressed in μg / m³. It is the resuspension flux of particulate heavy metals, expressed in μg / m² / s; It is the sediment resuspension rate, measured in kg / m² / s; It is the concentration of heavy metals per unit mass of sediment, expressed in μg / kg.

4. The method for heavy metal source tracing and impact assessment based on the coupling mechanism of multi-pathway migration of pollutants as described in claim 1, characterized in that: The forward simulation in step S5 specifically includes setting different hydrodynamic conditions, different pollution input concentrations, and different pollution control measures to simulate the entire migration and diffusion process of heavy metals in the watershed, outputting the concentration time process of each section along the river, and analyzing the concentration peak and the duration of exceeding the standard to assess the risk.

5. The method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants as described in claim 1, characterized in that: The reverse inference in step S5 specifically uses the constraint that the heavy metal concentration of the protected target section does not exceed the limit of the "Surface Water Environmental Quality Standard" to calculate the concentration threshold that each upstream control section needs to reach, providing a quantitative basis for optimizing treatment measures such as source control and process interception.

6. The method for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants as described in claim 1, characterized in that: The indoor experiments in step S4 include at least the following: determining the variation law of the dissolved-particulate partition coefficient by simulating different hydraulic disturbances and initial concentration conditions; determining the adsorption characteristic parameters of heavy metals in sediments by adsorption-desorption experiments; and simulating the release characteristics and risks of heavy metals in sediments under different hydrodynamic conditions by water tank experiments.

7. A system for source tracing and impact assessment of heavy metals based on the coupling mechanism of multi-pathway migration processes of pollutants, characterized in that, include: The data acquisition and monitoring unit is used to collect basic data of the target watershed, set up monitoring sections and stations, and acquire multiple rounds of hydrological, water quality and sediment monitoring data. The basic data includes the distribution of pollution sources, hydrological characteristics and current land use. The source analysis unit is used to analyze the changes in heavy metal concentration in water along the course of the river based on the acquired monitoring data, calculate the heavy metal flux at key sections, and comprehensively determine the composition of heavy metal pollution sources by combining the pollution source distribution in the basic data. The morphological analysis and risk assessment unit detects the content of different occurrence forms of heavy metals in water bodies and sediments, analyzes their spatiotemporal distribution characteristics, and analyzes the spatiotemporal distribution characteristics based on the monitoring data in step S1. The geoaccumulation index method is used to assess the heavy metal pollution level and release risk of sediments. The migration and transformation model construction and experimental unit is used to construct a migration and transformation model based on hydrological and water quality data from monitoring data and the morphological analysis results from the morphological analysis and risk assessment unit, which couples a hydrodynamic module, a sediment transport module, a heavy metal convection-diffusion transport module, and a sediment-water interface exchange module. The model is calibrated by measuring key parameters such as the dissolved-particulate partition coefficient and the adsorption-desorption coefficient through indoor experiments to obtain the calibrated migration and transformation model. The simulation and comprehensive evaluation unit is used to perform forward simulations under different operating conditions using a calibrated migration and transformation model, analyze the concentration change patterns and peak times of heavy metal migration, and assess the risks to downstream water quality. At the same time, with the target section water quality compliance as a constraint, it reverse-engineers the concentration control thresholds for each major section along the route and proposes corresponding pollution control optimization suggestions.

8. The system according to claim 7, characterized in that, The core mechanism of the migration and transformation model constructed in the experimental unit includes: considering the distribution relationship between dissolved and particulate heavy metals, driving the migration process through a hydrodynamic module, describing the carrier movement of heavy metals through a sediment transport module, simulating its transport in water through a heavy metal convection-diffusion transport module, and characterizing the exchange process of heavy metals between sediments and water through a sediment-water interface exchange module.

9. The system according to claim 7, characterized in that, The hydrodynamic module calculates the flow velocity, flow rate, and water level parameters of the water body by solving a set of two-dimensional shallow water equations; the sediment transport module describes the sedimentation, resuspension, and transport processes of sediment through sediment transport equations; the heavy metal convection-diffusion transport module establishes convection-diffusion equations for dissolved and particulate heavy metals respectively; and the sediment-water interface exchange module calculates the diffusion flux of dissolved heavy metals and the sedimentation and resuspension flux of particulate heavy metals through formulas.

10. The system according to claim 7, characterized in that, When the simulation and comprehensive evaluation unit conducts forward simulations, the set operating conditions include: different hydrodynamic conditions represented by flood processes of different frequencies, different pollution concentrations based on actual measurements or assumptions, and operating conditions of existing or failed pollution treatment measures.

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