A method and system for tracing the source of heavy metal pollution in watershed non-point sources

Abstract

A method and system for tracing the source of non-point source heavy metal pollution in a watershed, the method first determines the spatial distribution of soil heavy metal content under various land use types in the watershed, the sediment enrichment ratio and water solubility factor of soil heavy metals, and simulates the spatial and temporal distribution of rainfall runoff and soil erosion sand production, and then calculates the loss of land surface heavy metal pollution, and then combines the migration of heavy metal pollution in the river channel to calculate the loss of non-point source heavy metal pollution in the outflowing river section under various land use types, so as to obtain the contribution ratio of each land use type to the non-point source heavy metal pollution in the watershed, and finally determines the main source of the loss of heavy metal pollution in the watershed according to the contribution ratio. The present invention comprehensively considers the impact of land loss and river migration process on non-point source heavy metal pollution in the watershed, and can realize the accurate calculation of the loss load of non-point source heavy metal pollution at the watershed scale and the rapid and precise identification of pollution sources.

Description

Technical Field

[0001] The present invention belongs to the technical field of watershed non-point source pollution prevention and control, and specifically relates to a method and system for tracing the source of watershed non-point source heavy metal pollution. Background Art

[0002] Heavy metals are highly toxic and non-biodegradable. They easily accumulate in crops and aquatic organisms and enter the human body through the food chain, thus seriously endangering human health. In recent years, under the influence of human and natural activities such as the exploitation and utilization of mineral resources, the widespread use of pesticides and fertilizers, a large amount of heavy metals have accumulated in the soil and entered the surrounding rivers through rainfall runoff and soil erosion, causing serious water pollution in the basin. Timely understanding the spatiotemporal distribution of heavy metal pollution loss in the basin and identifying the main sources of heavy metal pollution in the basin will help to effectively and accurately prevent and control heavy metal pollution in the basin and reduce its potential adverse effects on the ecological environment and human health.

[0003] At present, the methods for analyzing the sources of heavy metal pollution loss from non-point sources in watersheds at home and abroad mainly include the pollution source emission inventory method, the empirical model method and the mechanism model method. The pollution source emission inventory method is to establish a pollution source inventory database by systematically counting the emission amount and emission factors of pollution sources, so as to qualitatively identify the source of heavy metals and quantitatively analyze the source of heavy metals. The empirical model method is to estimate the loss load of heavy metal pollution in the watershed by establishing the empirical relationship between environmental factors such as land use and heavy metal pollution, and determine the empirical coefficient, so as to analyze the source of heavy metal pollution. The mechanism model method is to simulate the migration process of heavy metals by comprehensively considering the generation, migration, transformation and aggregation of heavy metals in the environment, calculate the loss load of heavy metal pollution under different land use conditions, and then identify the main sources of pollution and their proportions. Although existing methods can realize the source identification of sudden heavy metal pollution events and long-term heavy metal accumulation pollution, the pollution source emission inventory method requires a systematic and comprehensive investigation of the entire watershed, which requires a large consumption of manpower and financial resources; the pollution source tracing results of the empirical model are less accurate; the construction and operation of the mechanism model require a large amount of fine data support. Therefore, the current methods are unable to achieve efficient analysis of the sources of non-point source heavy metal pollution loss in the watershed, which limits the precise prevention and control of heavy metal pollution loss in the watershed. Summary of the invention

[0004] The purpose of the present invention is to provide a method and system for tracing the source of heavy metal pollution in a watershed non-point source, which can accurately and efficiently determine the main sources of pollution, in response to the above-mentioned problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention proposes a method for tracing the source of non-point source heavy metal pollution in a watershed, comprising:

[0007] S1. Determine the spatial distribution of soil heavy metal content, sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types in the basin; simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield under various land use types in the basin;

[0008] S2. Calculate the loss of heavy metal pollution on the land surface of various land use types based on the results obtained in S1;

[0009] S3. Based on the amount of heavy metal pollution loss from the land surface of various land use types and the amount of heavy metal pollution migration from the land surface to the river channel, calculate the amount of non-point source heavy metal pollution loss in the outflow river section under various land use types, so as to obtain the contribution ratio of various land use types to non-point source heavy metal pollution in the basin;

[0010] S4. Determine the main sources of heavy metal pollution loss in the basin based on the contribution of various land use types to non-point source heavy metal pollution in the basin.

[0011] In S2, the loss of heavy metal pollution on the land surface of various land use types is calculated according to the following formula:

[0012] M land,i =(Load sed,i +Load surf,i )×Area i

[0013] Load sed,i =Q sed,i ×C soil,i ×α i

[0014] Load surf,i =Q surf,i ×C soil,i ×β i

[0015] In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type, C soil,i is the heavy metal content in the original soil of the i-th land use type, α i , β iare the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type respectively;

[0016] In S3, the non-point source heavy metal pollution loss of the outflow river section under various land use types is calculated according to the following formula:

[0017] M out,i =M land,i -M mig,i

[0018] In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,i is the loss of heavy metal pollution on land surface of the i-th land use type, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type;

[0019] The contribution of various land use types to non-point source heavy metal pollution in the watershed is calculated according to the following formula:

[0020]

[0021]

[0022] In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

[0023] In S3, the amount of heavy metal pollution transferred from the land surface to the river channel under various land use types is calculated according to the following formula:

[0024] M mig,i =M sed,i -M res,i -M dif,i +M bur,i

[0025] M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d

[0026] M res,i =M bed,i ×V res ×T r / T sed

[0027] M dif,i =(M bed,i ×MF bed -M che,i ×MF wat )×V dif ×T r / R d

[0028] M bur,i =M bed,i ×V bur ×T r / T sed

[0029] MF wat =1 / (1+K str ×C sed )

[0030] MF bed =1 / (1+K bed ×P bed )

[0031] In the above formula, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M dif,i M is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, MF wat is the mass fraction of dissolved heavy metals in river water, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the river depth, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer, MF bed is the mass fraction of dissolved heavy metals in river sediment, V dif is the diffusion rate of heavy metals, V bur is the burial rate of heavy metals, Kstr is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediments, C sed is the sediment concentration, P bed It is the bulk density of sediment.

[0032] In S1, the spatial distribution of soil heavy metal content under various land use types is obtained by collecting original surface soil under various land use types in the watershed using a grid point distribution method and measuring the heavy metal content;

[0033] The sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types were calculated according to the following formula:

[0034]

[0035] In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type, respectively. sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type.

[0036] In S1, the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin were simulated using the SWAT model.

[0037] In the second aspect, the present invention proposes a watershed non-point source heavy metal pollution tracing system, comprising:

[0038] The measurement module is used to measure the spatial distribution of soil heavy metal content, sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types in the basin;

[0039] The simulation module is used to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin;

[0040] The land surface loss calculation module is used to calculate the land surface heavy metal pollution loss of various land use types based on the output results of the measurement module and the simulation module;

[0041] The river migration calculation module is used to calculate the migration amount of heavy metal pollution from the land surface to the river under various land use types;

[0042] The contribution ratio calculation module is used to calculate the non-point source heavy metal pollution loss of the outflowing river section under various land use types based on the output results of the land loss calculation module and the river migration calculation module, so as to obtain the contribution ratio of various land use types to the non-point source heavy metal pollution in the basin;

[0043] The main pollution source determination module is used to determine the main sources of heavy metal pollution loss in the basin based on the output results of the contribution ratio calculation module.

[0044] The land surface loss calculation module calculates the land surface heavy metal pollution loss of various land use types according to the following formula:

[0045] M land,i =(Load sed,i +Load surf,i )×Area i

[0046] Load sed,i =Q sed,i ×C soil,i ×α i

[0047] Load surf,i =Q surf,i ×C soil,i ×β i

[0048] In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type, C soil,i is the heavy metal content in the original soil of the i-th land use type, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type respectively;

[0049] The contribution ratio calculation module calculates the non-point source heavy metal pollution loss of the outflow river section under various land use types according to the following formula:

[0050] M out,i =M land,i -M mig,i

[0051] In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,i is the loss of heavy metal pollution on land surface of the i-th land use type, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type;

[0052] The contribution of various land use types to non-point source heavy metal pollution in the watershed is calculated according to the following formula:

[0053]

[0054] In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

[0055] The river migration amount calculation module calculates the heavy metal pollution migration amount of pollution lost from the land surface and migrated to the river under various land use types according to the following formula:

[0056] M mig,i =M sed,i -M res,i -M dif,i +M bur,i

[0057] M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d

[0058] M res,i =M bed,i ×V res ×T r / T sed

[0059] M dif,i =(M bed,i ×MF bed -M che,i ×MF wat )×V dif ×T r / R d

[0060] M bur,i =M bed,i ×V bur ×T r / Tsed

[0061] MF wat =1 / (1+K str ×C sed )

[0062] MF bed =1 / (1+K bed ×P bed )

[0063] In the above formula, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M dif,i M is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, MF wat is the mass fraction of dissolved heavy metals in river water, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the river depth, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer, MF bed is the mass fraction of dissolved heavy metals in river sediment, V dif is the diffusion rate of heavy metals, V bur is the burial rate of heavy metals, K str is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediments, C sed is the sediment concentration, P bed It is the bulk density of sediment.

[0064] The sediment enrichment ratio and water solubility factor calculation module calculates the sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types according to the following formula:

[0065]

[0066] In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type, respectively. sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type.

[0067] The simulation module uses the SWAT model to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] The method for tracing the source of non-point source heavy metal pollution in a watershed of the present invention first determines the spatial distribution of soil heavy metal content, the sediment enrichment ratio and the water solubility factor of soil heavy metals under various land use types in the watershed, and simulates the spatiotemporal distribution of rainfall runoff and soil erosion sediment yield under various land use types in the watershed, and then calculates the total load of land surface heavy metal pollution loss of various land use types, and then calculates the non-point source heavy metal pollution loss of outflowing river sections under various land use types based on the total load of land surface heavy metal pollution loss of various land use types and the heavy metal pollution load migrated from the pollution load lost from the land surface, so as to obtain the contribution ratio of various land use types to the non-point source heavy metal pollution in the watershed, and finally determines the main source of heavy metal pollution loss in the watershed according to the contribution ratio of various land use types to the non-point source heavy metal pollution in the watershed. This method couples empirical models, watershed hydrological models and on-site monitoring methods, fully considering the heavy metal loss load caused by rainfall runoff and soil erosion at different spatial locations on the basin's land surface, as well as the impact of river migration on heavy metal pollution loss, and obtains the heavy metal pollution load entering the basin's water environment and the contribution of pollution sources of each land use type. It can realize the accurate calculation of the basin-scale non-point source heavy metal pollution loss load and the rapid and precise identification of pollution sources, which is helpful to identify the spatiotemporal heterogeneity of non-point source heavy metal pollution loss in the basin, and also helps to accurately prevent and control heavy metal pollution in the basin's water environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 The flowchart of the method of the present invention is shown in FIG.

[0071] Figure 2 This is a schematic diagram of the spatial distribution of heavy metal content in the watershed soil in Example 1.

[0072] Figure 3This is a schematic diagram of the spatial distribution of rainfall runoff and soil erosion sediment yield in the basin in Example 1.

[0073] Figure 4 This is a schematic diagram of the spatial distribution of the non-point source heavy metal pollution loss in the outflow river section in Example 1.

[0074] Figure 5 This is a schematic diagram of the proportion of land use in the watershed and the proportion of non-point source heavy metal loss in the watershed in Example 1.

[0075] Figure 6 The structure diagram of the system of the present invention is shown in FIG. DETAILED DESCRIPTION

[0076] The present invention proposes a method and system for tracing the source of non-point source heavy metal pollution in a watershed. The method obtains the spatial distribution of soil heavy metal pollution in the watershed, the soil heavy metal sediment enrichment ratio and the soil heavy metal water solubility factor based on measured data, combines the soil erosion sediment yield and rainfall runoff output by the watershed hydrological model, calculates the load characteristics of land surface heavy metal pollution loss, and considers the impact of the transformation process between the dissolved phase and the adsorbed phase during river channel migration on the loss of heavy metal pollution, thereby accurately calculating the loss of non-point source heavy metal pollution in the outflow river section, and finally quickly identifying the source of the loss of non-point source heavy metal pollution in the watershed.

[0077] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0078] Embodiment 1:

[0079] This embodiment takes a typical river basin as an example to implement a river basin non-point source heavy metal pollution tracing method described in the present invention. Figure 1 As shown, the specific steps are as follows:

[0080] 1. Grid-like points were set up in the watershed to collect the original soil from the surface of various land use types. After sampling, the samples were bagged and stored on site and brought back to the laboratory as soon as possible. After the samples were naturally air-dried, impurities were removed and ground through a 100-mesh nylon sieve. 3 -HF-HClO 4 The heavy metal contents were determined by inductively coupled plasma emission spectrometry. Figure 2 The spatial distribution of soil heavy metal content under various land use types is shown, where the land use types include agricultural land (dry land, rice fields), forests, grasslands, construction land, etc.

[0081] 2. Select plots of various typical land use types in the basin to carry out natural rainfall runoff monitoring experiments. During natural rainfall, the rainfall runoff volume, sediment yield, and heavy metal content in rainfall runoff and sediment were measured after each rainfall runoff. Using the measured heavy metal content in sediment and rainfall runoff, as well as the heavy metal content in the original soil, the sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types were calculated according to the following formula:

[0082]

[0083] In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type, respectively. sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type, obtained by detection in step 1.

[0084] 3. The SWAT model is used to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield for various land use types in the basin.

[0085] The SWAT model needs to construct a digital elevation model, land use spatial distribution data, soil type data, meteorological data and watershed management data of the study area. The digital elevation model uses a 30m×30m resolution model provided by the geospatial data cloud; the land use spatial distribution data is obtained by interpreting the land use type through remote sensing images of the study area; the soil type data is obtained through soil type distribution maps and field sampling surveys; the meteorological data is obtained through the China Meteorological Data Network or local meteorological stations; the watershed management data is obtained through field surveys to obtain data such as agricultural production activities in the study area.

[0086] After obtaining the data required by the above SWAT model, the data was input into the model, and the model parameters were calibrated and verified using the measured runoff and sediment yield data. The adjusted model was used to simulate the temporal and spatial distribution of basin runoff and soil erosion sediment yield, and the following results were obtained: Figure 3 The temporal and spatial distribution of rainfall runoff and soil erosion sediment yield for various land use types are shown.

[0087] 4. Based on the spatial distribution of heavy metal content in the watershed soil obtained in step 1, the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of various land use types obtained in step 2, and the spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types obtained in step 3, the following formula is used to calculate the loss of heavy metal pollution on the land surface. The results are as follows: Figure 4As shown:

[0088] M land,i =(Load sed,i +Load surf,i )×Area i

[0089] Load sed,i =Q sed,i ×C soil,i ×α i

[0090] Load surf,i =Q surf,i ×C soil,i ×β i

[0091] In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type respectively.

[0092] 5. Calculate the amount of heavy metal pollution that migrates from land to river channels

[0093] The process of heavy metal pollution lost from the land surface and migrating into the river is mainly the process of sedimentation, resuspension, diffusion and burial between the dissolved phase and the adsorbed phase.

[0094] (1) The mass fraction of heavy metals in the dissolved phase in the river water and the dissolved phase in the river sediment is used to calculate the distribution of dissolved phase and adsorbed phase. The mass fraction of heavy metals in the dissolved phase is calculated as follows:

[0095] MF wat =1 / (1+K str ×C sed )

[0096] MF bed =1 / (1+K bed ×P bed )

[0097] In the above formula, MF wat is the mass fraction of dissolved heavy metals in river water, MF bed is the mass fraction of dissolved heavy metals in river sediment, Kstr is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediments, C sed is the sediment concentration, P bed It is the bulk density of sediment.

[0098] (2) Calculation of the amount of heavy metals transferred by sedimentation, resuspension, diffusion and burial, where:

[0099] The calculation formula for the amount of adsorbed heavy metals entering the sediment from the water body through sedimentation is as follows:

[0100] M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d

[0101] In the above formula, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the depth of the river.

[0102] The formula for calculating the amount of heavy metals entering the water body from the sediment through resuspension is as follows:

[0103] M res,i =M bed,i ×V res ×T r / T sed

[0104] In the above formula, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer.

[0105] The calculation formula for the amount of heavy metals transported from water bodies by diffusion is as follows:

[0106] M dif,i =(M bed,i ×MF bed -Mche,i ×MF wat )×V dif ×T r / R d

[0107] In the above formula, M dif,i is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, V dif is the diffusion rate of heavy metals.

[0108] The calculation formula for the amount of heavy metals transferred from surface sediment to deep sediment through burial is as follows:

[0109] M bur,i =M bed,i ×V bur ×T r / T sed

[0110] In the above formula, M bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, V bur is the landfill rate of heavy metals.

[0111] (3) Based on the amount of heavy metals in the four migration processes of sedimentation, resuspension, diffusion and burial, the amount of heavy metal pollution that migrates from the land surface to the river under various land use types is calculated:

[0112] M mig,i =M sed,i -M res,i -M dif,i +M bur,i

[0113] In the above formula, M mig,i is the amount of heavy metal pollution that migrates from land surface to river channels under the i-th land use type.

[0114] 6. Based on the total load of heavy metal pollution loss from the land surface of various land use types and the amount of heavy metal pollution that migrates from the pollution load lost from the land surface to the river channel, the non-point source heavy metal pollution loss of the outflow river section under various land use types is calculated according to the following formula:

[0115] M out,i =M land,i -M mig,i

[0116] In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,iis the loss of heavy metal pollution on land surface of the i-th land use type, M mig,i is the amount of heavy metal pollution that migrates from land surface to river channels under the i-th land use type.

[0117] 7. Calculate the contribution of various land use types to non-point source heavy metal pollution in the watershed according to the following formula. The results are as follows: Figure 5 As shown:

[0118]

[0119] In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

[0120] 8. According to the contribution of various land use types to non-point source heavy metal pollution in the basin, the main sources of heavy metal pollution loss in the basin are determined, and targeted guidance and suggestions are provided for the formulation of basin water environment management policies.

[0121] In this embodiment, the land use type with the largest contribution is agricultural land, thus determining that the main source of non-point source heavy metal pollution loss is agricultural land, especially the non-point source heavy metal pollution loss of dry land accounts for 32%, and the non-point source pollution loss of rice fields accounts for 41%. Therefore, in local watershed management, attention should be paid to the non-point source heavy metal pollution loss of agricultural land.

[0122] Embodiment 2:

[0123] A basin non-point source heavy metal pollution tracing system, such as Figure 6 As shown, it includes a measurement module, a simulation module, a total land surface loss load calculation module, a river migration calculation module, a contribution ratio calculation module, and a main pollution source determination module.

[0124] The determination module is used to determine the spatial distribution of soil heavy metal content under various land use types in the basin, the sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types in the basin, wherein:

[0125] The spatial distribution of soil heavy metal content under various land use types was obtained by collecting the original surface soil under various land use types using the grid point method in the watershed and measuring the heavy metal content;

[0126] The sediment enrichment ratio and water solubility factor calculation module calculates the sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types according to the following formula:

[0127]

[0128] In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio (dimensionless) and soil heavy metal water solubility factor of the i-th land use type, C sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type.

[0129] The simulation module adopts the SWAT model simulation module to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin.

[0130] The land surface loss total load calculation module is used to calculate the land surface heavy metal pollution loss of various land use types according to the following formula based on the output results of the measurement module and the simulation module:

[0131] M land,i =(Load sed,i +Load surf,i )×Area i

[0132] Load sed,i =Q sed,i ×C soil,i ×α i

[0133] Load surf,i =Q surf,i ×C soil,i ×β i

[0134] In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type, C soil,i is the heavy metal content in the original soil of the i-th land use type, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type respectively.

[0135] M land,i is the loss of heavy metal pollution on land surface of the i-th land use type (kg), Load sed,i 、Load surf,i are the land surface heavy metal pollution load (kg / hm2) lost with soil erosion and the land surface heavy metal pollution load (kg / hm2) lost with rainfall runoff of the i-th land use type, Q sed,i , Q surf,i are the soil erosion sediment yield (t / hm2) and rainfall runoff (mm) of the i-th land use type respectively.

[0136] The river migration amount calculation module is used to calculate the heavy metal pollution migration amount of pollution lost from the land surface and migrated to the river under various land use types according to the following formula:

[0137] M mig,i =M sed,i -M res,i -M dif,i +M bur,i

[0138] M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d

[0139] M res,i =M bed,i ×V res ×T r / T sed

[0140] M dif,i =(M bed,i ×MF bed -M che,i ×MF wat )×V dif ×T r / R d

[0141] M bur,i =M bed,i ×V bur ×T r / T sed

[0142] MF wat =1 / (1+K str ×C sed )

[0143] MF bed =1 / (1+K bed ×Pbed )

[0144] In the above formula, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M dif,i M is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, MF wat is the mass fraction of dissolved heavy metals in river water, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the river depth, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer, MF bed is the mass fraction of dissolved heavy metals in river sediment, V dif is the diffusion rate of heavy metals, V bur is the burial rate of heavy metals, K str is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediments, C sed is the sediment concentration, P bed It is the bulk density of sediment.

[0145] The contribution ratio calculation module is used to calculate the non-point source heavy metal pollution loss of the outflow river section under various land use types based on the output results of the land surface loss total load calculation module and the river migration calculation module, so as to obtain the contribution ratio of various land use types to the non-point source heavy metal pollution in the basin, wherein:

[0146] The calculation formula for the loss of non-point source heavy metal pollution in the outflow river section under various land use types is:

[0147] M out,i =M land,i -M mig,i

[0148] In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,i is the loss of heavy metal pollution on land surface of the i-th land use type, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type;

[0149] The calculation formula for the contribution of various land use types to non-point source heavy metal pollution in the watershed is:

[0150]

[0151] In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

[0152] The main pollution source determination module is used to determine the main sources of heavy metal pollution loss in the watershed according to the output results of the contribution ratio calculation module.

Claims

1. A method for tracing the source of non-point source heavy metal pollution in a watershed, characterized in that: The method comprises: S1. Determine the spatial distribution of soil heavy metal content, sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types in the basin; simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield under various land use types in the basin; S2. Calculate the loss of heavy metal pollution on the land surface of various land use types based on the results obtained in S1; S3. Based on the amount of heavy metal pollution loss from the land surface of various land use types and the amount of heavy metal pollution migration from the land surface to the river channel, calculate the amount of non-point source heavy metal pollution loss in the outflow river section under various land use types, so as to obtain the contribution ratio of various land use types to non-point source heavy metal pollution in the basin; S4. Determine the main sources of heavy metal pollution loss in the basin based on the contribution of various land use types to non-point source heavy metal pollution in the basin.

2. A method for tracing the source of heavy metal pollution in a watershed according to claim 1, characterized in that: In S2, the loss of heavy metal pollution on the land surface of various land use types is calculated according to the following formula: M land,i =(Load sed,i +Load surf,i )×Area i Load sed,i =Q sed,i ×C soil,i ×α i Load surf,i =Q surf,i ×C soil,i ×β i In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type, C soil,i is the heavy metal content in the original soil of the i-th land use type, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type respectively; In S3, the non-point source heavy metal pollution loss of the outflow river section under various land use types is calculated according to the following formula: M out,i =M land,i -M mig,i In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,i is the land surface heavy metal pollution loss of the i-th land use type, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type; The contribution of various land use types to non-point source heavy metal pollution in the watershed is calculated according to the following formula: In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

3. A method for tracing the source of heavy metal pollution in a watershed according to claim 1 or 2, characterized in that: In S3, the amount of heavy metal pollution transferred from the land surface to the river channel under various land use types is calculated according to the following formula: M mig,i =M sed,i -M res,i -M dif,i +M bur,i M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d M res,i =M bed,i ×V res ×T r / T sed M dif,i =(M bed,i ×MF bed -M che,i ×MF wat )×V dif ×T r / R d M bur,i =M bed,i ×V bur ×T r / T sed MF wat =1 / (1+K str ×C sed ) MF bed =1 / (1+K bed ×P bed ) In the above formula, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M dif,i M is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, MF wat is the mass fraction of dissolved heavy metals in river water, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the river depth, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer, MF bed is the mass fraction of dissolved heavy metals in river sediment, V dif is the diffusion rate of heavy metals, V bur is the burial rate of heavy metals, K str is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediment, C sed is the sediment concentration, P bed It is the bulk density of sediment.

4. A method for tracing the source of non-point source heavy metal pollution in a watershed according to claim 1 or 2, characterized in that: In S1, the spatial distribution of soil heavy metal content under various land use types is obtained by collecting original surface soil under various land use types in the watershed using a grid point distribution method and measuring the heavy metal content; The sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types were calculated according to the following formula: In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type, respectively. sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type.

5. A method for tracing the source of non-point source heavy metal pollution in a watershed according to claim 1 or 2, characterized in that: In S1, the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin were simulated using the SWAT model.

6. A basin non-point source heavy metal pollution tracing system, characterized in that: The system comprises: The measurement module is used to measure the spatial distribution of soil heavy metal content, sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types in the basin; The simulation module is used to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin; The land surface loss calculation module is used to calculate the land surface heavy metal pollution loss of various land use types based on the output results of the measurement module and the simulation module; The river migration calculation module is used to calculate the migration amount of heavy metal pollution from land surface to river under various land use types; The contribution ratio calculation module is used to calculate the non-point source heavy metal pollution loss of the outflowing river section under various land use types based on the output results of the land loss calculation module and the river migration calculation module, so as to obtain the contribution ratio of various land use types to the non-point source heavy metal pollution in the basin; The main pollution source determination module is used to determine the main sources of heavy metal pollution loss in the basin based on the output results of the contribution ratio calculation module.

7. A basin non-point source heavy metal pollution tracing system according to claim 6, characterized in that: The land surface loss calculation module calculates the land surface heavy metal pollution loss of various land use types according to the following formula: M land,i =(Load sed,i +Load surf,i )×Area i Load sed,i =Q sed,i ×C soil,i ×α i Load surf,i =Q surf,i ×C soil,i ×β i In the above formula, M land,i is the loss of heavy metal pollution on the land surface of the i-th land use type, Load sed,i 、Load surf,i are the land surface heavy metal pollution load lost with soil erosion and the land surface heavy metal pollution load lost with rainfall runoff of the i-th land use type, Area i is the land area of ​​the i-th land use type, Q sed,i , Q surf,i are the soil erosion and sediment yield and rainfall runoff of the i-th land use type, C soil,i is the heavy metal content in the original soil of the i-th land use type, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type respectively; The contribution ratio calculation module calculates the non-point source heavy metal pollution loss of the outflow river section under various land use types according to the following formula: M out,i =M land,i -M mig,i In the above formula, M out,i is the non-point source heavy metal pollution loss in the outflow river section under the i-th land use type, M land,i is the land surface heavy metal pollution loss of the i-th land use type, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type; The contribution of various land use types to non-point source heavy metal pollution in the watershed is calculated according to the following formula: In the above formula, Contri i is the contribution of the i-th land use type to the non-point source heavy metal pollution in the watershed, M out is the total amount of non-point source heavy metal pollution loss at the outlet of the entire basin, and n is the number of land use types.

8. A watershed non-point source heavy metal pollution tracing system according to claim 6 or 7, characterized in that: The river migration amount calculation module calculates the heavy metal pollution migration amount of pollution lost from the land surface and migrated to the river under various land use types according to the following formula: M mig,i =M sed,i -M res,i -M dif,i +M bur,i M sed,i =M che,i ×(1-MF wat )×V sed ×T r / R d M res,i =M bed,i ×V res ×T r / T sed M dif,i =(M bed,i ×MF bed -M che,i ×MF wat )×V dif ×T r / R d M bur,i =M bed,i ×V bur ×T r / T sed MF wat =1 / (1+K str ×C sed ) MF bed =1 / (1+K bed ×P bed ) In the above formula, M mig,i is the amount of heavy metal pollution transferred from land surface to river channel under the i-th land use type, M sed,i is the amount of heavy metals removed from the water body by sedimentation from the pollution lost from the land surface under the i-th land use type, M res,i is the amount of heavy metals that enter the water body from the sediment through resuspension due to pollution loss from the land surface under the i-th land use type, M dif,i M is the amount of heavy metals transported from the water body by diffusion from the pollution lost from the land surface under the i-th land use type, bur,i is the amount of heavy metals transferred from the surface sediment to the deep sediment through burial under the i-th land use type, M che,i is the amount of heavy metals that enter the river from the land surface under the i-th land use type, MF wat is the mass fraction of dissolved heavy metals in river water, V sed is the sedimentation rate of heavy metals, T r is the river flow time, R d is the river depth, M bed,i is the amount of heavy metals that enter the river sediment from the land surface under the i-th land use type, V res is the resuspension rate of heavy metals, T sed is the thickness of the riverbed mud layer, MF bed is the mass fraction of dissolved heavy metals in river sediment, V dif is the diffusion rate of heavy metals, V bur is the burial rate of heavy metals, K str is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river water, K bed is the distribution coefficient of heavy metals in dissolved and adsorbed phases in river sediment, C sed is the sediment concentration, P bed It is the bulk density of sediment.

9. A watershed non-point source heavy metal pollution tracing system according to claim 6 or 7, characterized in that: The sediment enrichment ratio and water solubility factor calculation module calculates the sediment enrichment ratio and water solubility factor of soil heavy metals under various land use types according to the following formula: In the above formula, α i , β i are the soil heavy metal sediment enrichment ratio and soil heavy metal water solubility factor of the i-th land use type, respectively. sed,i , C surf,i are the sediment generated by rainfall runoff of the i-th land use type, the heavy metal content in the runoff, and C soil,i is the heavy metal content in the original soil of the i-th land use type.

10. A watershed non-point source heavy metal pollution tracing system according to claim 6 or 7, characterized in that: The simulation module uses the SWAT model to simulate the temporal and spatial distribution of rainfall runoff and soil erosion sediment yield of various land use types in the basin.

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