An arid land differentiation point laying underground infiltration water sampling method based on slope grading

Abstract

The application discloses a kind of dry land differentiation based on slope grading and places underground percolation water sampling method of point, belong to cultivated soil heavy metal migration research field, including sampling area determination, sampling point determination and sample collection step.The application utilizes GIS to divide unit when determining sampling area, and the initial sampling area quantity is distributed according to the proportion distribution of each unit, and the sampling weight of sensitive area is increased, so that the representative and precision of sampling area are improved by eliminating the omission of sampling area caused by ignoring topographic heterogeneity in traditional method;The application breaks through the limitation of traditional single grid or cross point, and implements the differential sampling point layout strategy, so that the coefficient of variation of underground percolation water heavy metal concentration captured in the medium slope area is more accurate, the significant difference of heavy metal concentration at different slope positions (upper, middle and lower) of slope surface is reflected, and the spatial heterogeneity under slope surface scale is effectively captured.

Description

Technical Field

[0001] This invention belongs to the field of research technology on heavy metal migration in arable land soil, specifically involving a method for sampling groundwater infiltration in dry land based on slope classification. Background Technology

[0002] In carrying out the investigation of the causes of heavy metal pollution in arable land soil, it is necessary to determine the input and output fluxes of heavy metals in arable land soil in order to assess changes in soil environmental quality. Among these, the collection of groundwater infiltration from arable land soil and the analysis of heavy metal content are important components.

[0003] Currently, there are no clear technical guidelines or standards for the placement of groundwater infiltration monitoring points in arable land. The technical guidelines for investigating the causes of heavy metal pollution in arable land only propose placing infiltration monitoring points based on factors such as soil type, parent material type, and topographic features, with a general rule of three points per survey and monitoring area. However, in practice, the survey and monitoring areas are typically large, resulting in only one monitoring point being placed on each actual plot, which is not representative.

[0004] Nearly 70% of Yunnan's arable land is sloping, with an average slope of about 15°. For sloping farmland, irrigation is virtually nonexistent, relying solely on rainfall. During rainfall, the duration of water retention varies depending on the slope, and soil type also affects the amount of groundwater collected, leading to significant differences. Therefore, the selection of groundwater infiltration points for investigation is limited and lacks representativeness. Furthermore, the investigation requires collecting groundwater samples during irrigation, wet, dry, and normal water periods, involving multiple soil excavations, requiring substantial manpower, and potentially interfering with the sample collection.

[0005] Therefore, there is an urgent need to find a differentiated sampling method for groundwater infiltration in dry land with sloping terrain classification. Summary of the Invention

[0006] To address the challenges posed by the fact that most mountainous farmlands are sloping, have diverse soil types, uneven rainfall distribution, and reduced rainwater infiltration with decreasing slope during rainfall, and to resolve the technical problem of low sampling accuracy in existing technologies, this invention aims to provide a differentiated groundwater sampling method for dryland based on slope grading.

[0007] The objective of this invention is achieved by including the following steps: S1. Sampling area determination: S101. Data Acquisition: Collect data on sloping dryland farmland, including: digital elevation model data, soil type distribution map, land use status map, and spatial distribution map of polluted farmland.

[0008] S102. Slope Classification: Based on the acquired digital elevation model data, a slope raster layer is generated using a geographic information system (such as ArcGIS, QGIS, etc.). The dry farmland is divided into three levels according to the slope: gentle slope, medium slope, and steep slope, and a slope classification vector map is generated.

[0009] S103. Generate composite units: In the GIS platform, the generated slope classification vector map is spatially overlaid with the spatial distribution map of polluted farmland (safe use type and strictly controlled type). Through intersection operation, the polluted farmland is divided and grouped into several composite units of slope level and pollution category; each composite unit represents a set of farmland with the same slope characteristics and the same pollution category.

[0010] S104. Preliminary determination of sampling areas: Calculate the area of ​​each composite unit and its proportion to the total area of ​​polluted farmland; based on the preset total number of sampling areas, make preliminary allocations according to the area proportion of each composite unit, and calculate the initial theoretical sampling number of each unit; then make corrections to ensure that each pollution category (safe utilization category, strictly controlled category) has at least one sampling area under different slope levels; since the risk of soil and water migration is higher in medium slope areas, for medium slope areas, the sampling weight is increased for plots located in the middle and lower part of the slope, near ditches or residential areas; S105. Determine the final sampling area: Cover the target composite unit with a regular grid, randomly select a grid as the starting point, calculate the sampling interval according to the theoretical sampling number of the unit, and systematically select grids; within the finally selected grids, select farmland plots with an area greater than 2 mu, clear boundaries, contiguous cultivation, and on-site operation conditions, and finally determine them as the sampling area, and record their center coordinates and boundary range. S2. Sampling point determination: Sampling area on gentle slope: A core sampling point is set up at the geometric center of the area, and then a boundary control sampling point is set up near the boundary in at least two directions from the core sampling point. This sampling point layout method focuses on the internal homogeneity while strengthening the control of potential inputs and outputs at the boundary. Sampling area on medium slope: Establish a main longitudinal profile along the direction of maximum slope. Establish core sampling points longitudinally at the upper, middle, and lower slope positions of the main longitudinal profile. Then, establish transverse sampling zones along contour lines centered on each core sampling point. Place at least 3 sampling points on each transverse sampling zone to capture transverse variation. Place 3 points at equal intervals on each transverse sampling zone. Simultaneously, add 3 auxiliary monitoring points to the longitudinal profile of the slope. Steep slope sampling area: First, follow the same sampling method as the medium slope sampling area to set up core sampling points, transverse sampling points, and auxiliary monitoring points. Then, through on-site surveys or topographic analysis, identify all natural channels, fissure zones, or concentrated outflow points that collect water from the steep slope area. Set up boundary sampling points at the junction of each confluence path that is about to leave the steep slope area and enter the stable area. On the boundary line between the steep slope farmland and the safe area below, set up early warning sampling points at intervals as early warning points for whether pollutants have crossed the boundary and spread. S3. Collection of leachate samples: S301. Remove vegetation debris and other waste from the surface of the sampling point to expose the natural soil surface; S302. Excavate a pit with a cross-sectional dimension larger than the initial pit of the infiltration water collector at the marked point; S303. The excavated soil is piled up in an orderly manner next to the pit according to the natural occurrence layers, and the depth, color, texture and moisture of each layer are recorded. S304. Set the burial depth of the leachate collector according to Table 1 and collect leachate; Table 1 Burial Depth Table .

[0011] Preferably, the slope of the gentle slope is ≤6°, the slope of the medium slope is >6° and ≤25°, and the slope of the steep slope is >25°.

[0012] Preferably, in step S2: For the sampling area on a gentle slope: starting from the core sampling point, extend towards the boundary in two perpendicular directions, and set up two boundary control sampling points near the boundary of the plot; a total of 5 sampling points are set up in each gentle slope sampling area; For medium-slope sampling areas: there are 3 sampling points in each transverse sampling zone. On each transverse sampling zone, 3 points are arranged at equal intervals, located at the center of the transverse sampling zone, the left side of the transverse sampling zone, and the right side of the transverse sampling zone, respectively; there are a total of 15 sampling points in each medium-slope sampling area. For steep slope sampling areas: the number of boundary sampling points at each intersection is 1, and the number of warning sampling points in each steep slope sampling area is 3 to 5.

[0013] Preferably, the infiltration collector at each sampling point collects both lateral and vertical infiltration water from the soil, and the lateral and vertical infiltration water are stored independently.

[0014] Preferably, the leachate collector includes a first storage tank, a second storage tank, and a pump. The first storage tank is square, and the second storage tank is cylindrical. The bottoms of the first and second storage tanks are connected by a pipe, and the bottom of the first storage tank is 10cm to 20cm higher than the bottom of the second storage tank. The first storage tank has an inlet, and from the inside out, a perforated partition, a filter membrane layer, a river sand layer, and a filter cotton layer are arranged sequentially, with the filter cotton layer covering the inlet. The second storage tank has an insertion port at the top, with a guide sleeve on the port. The pump is inserted into the second storage tank from top to bottom through the guide sleeve. The pump head is equipped with a one-way valve. Both the first and second storage tanks are buried in the soil, with the upper part of the guide sleeve and the upper part of the pump above the soil.

[0015] Preferably, the inlet of the first liquid storage tank is located on the top or side of the first liquid storage tank.

[0016] The first storage tank is a square box made of corrosion-resistant, non-absorbent inert material (such as high-density polyethylene, HDPE). Its internal volume is set according to sampling requirements (e.g., length × width × height = 30cm × 30cm × 40cm). The first storage tank has a water inlet on the top or side. The top water inlet is used to collect vertically flowing leachate, and the side water inlet is used to collect laterally flowing leachate.

[0017] The perforated partition is made of perforated rigid PVC board with a thickness of 3~5mm, a hole diameter of 3~5mm, a hole spacing of 10~15mm, and an opening rate of about 30%~40%.

[0018] The filter membrane layer uses polyethersulfone (PES) or polyvinylidene fluoride (PVDF) microporous filter membrane with a pore size of 0.45μm, which can effectively intercept suspended particles, colloids and microorganisms, while avoiding the adsorption of dissolved chemical components (such as nitrogen, phosphorus and heavy metals); 2 to 3 filter membrane layers can be set to increase the effective filtration area.

[0019] The river sand layer is made of natural quartz sand with a particle size of 0.5~1.0mm, which is acid washed and dried to remove background pollutants. The thickness of the river sand layer is 10cm~15cm, and the filling density is moderate. Its function is to simulate the filtration process of natural soil media and prevent filter cotton debris from clogging the microporous filter membrane.

[0020] The filter layer is made of polyester fiber nonwoven fabric with a thickness of 2-3cm (specification 200g / m). 2 ~300g / m 2 With a porosity of >90%, this layer can intercept coarse particles, root debris, and fallen matter, extending the service life of the lower filter media and making it easy to replace.

[0021] The second storage tank is a cylindrical tank made of the same material as the first storage tank. Its volume is typically 1 to 2 times that of the first storage tank (e.g., 20cm in diameter and 50cm in height). The connecting pipe between the bottom of the first and second storage tanks is usually made of polytetrafluoroethylene (PTFE). Utilizing the natural elevation difference, the leachate collected in the first storage tank automatically flows into the second storage tank for storage.

[0022] The guide sleeve is made of polytetrafluoroethylene or rubber and has a sealing ring to guide the vertical insertion of the pump and prevent external impurities from entering.

[0023] The extractor is a manual or electric piston-type extractor, with a one-way valve to ensure that the water sample does not flow back during extraction. The upper port of the guide sleeve is 10-15cm above the ground.

[0024] Compared with the prior art, the present invention has the following technical effects: 1. Compared with traditional sampling methods, this invention uses GIS to divide the project area into units by overlaying the elevation, polluted farmland patches, and slope when determining the sampling area. The initial number of sampling areas is allocated according to the proportional distribution of each unit, and the sampling weight is increased for sensitive areas. This eliminates the omission of sampling areas caused by ignoring the heterogeneity of the landform in traditional methods, and improves the representativeness and accuracy of the sampling area. 2. This invention breaks through the limitations of traditional single grid or cross-shaped sampling point layout, and implements a differentiated sampling point layout strategy. The coefficient of variation of heavy metal concentration in groundwater captured in medium slope areas is more accurate, reflecting the significant differences in heavy metal concentration at different slope positions (upper, middle and lower), and effectively capturing the spatial heterogeneity at the slope scale. 3. The infiltration water sampler of this invention adopts a filtration and grading design to simulate the migration process of soil water in natural media. It can remove interfering particles without changing the original concentration of dissolved components in the water sample. Simultaneously, it collects infiltration water from both lateral and vertical flows of soil, storing the two types of water samples independently to avoid mixing of water from different sources. The obtained samples can more completely reflect the actual transport of pollutants in the slope soil. Using the infiltration water sampler, only one installation is required, and subsequent operations only require surface pumping, saving manpower and avoiding damage to the soil structure and interference with the infiltrated water quality caused by repeated excavation. Attached Figure Description

[0025] Figure 1 A schematic diagram of sampling points in a gentle slope sampling area; Figure 2 A schematic diagram of sampling points in a medium-slope sampling area; Figure 3 This is a schematic diagram of sampling points in the steep slope sampling area; Figure 4 This is a schematic diagram of the percolation water collector of the present invention with the water inlet located at the top; Figure 5 This is a schematic diagram of the percolation water collector of the present invention with the inlet located on the side. In the diagram: 1-First liquid storage tank, 2-Second liquid storage tank, 3-Liquid extractor, 4-Perforated partition, 5-Filter membrane layer, 6-River sand layer, 7-Filter cotton layer, 8-Guide sleeve, 9-Liquid extraction head, 10-One-way valve, 11-Soil layer. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention. Example 1

[0027] A typical mountainous area in a county of Yunnan Province, with a study area of ​​approximately 5 km², an average slope of 15°, and a maximum slope of 28°. Groundwater infiltration sampling points were established within this area for monitoring heavy metal migration fluxes during four different hydrological periods over a subsequent year. The specific implementation process is as follows: This embodiment uses a differentiated groundwater infiltration sampling method based on slope grading for dryland areas, including the following steps: S1. Sampling area determination: S101. Data Acquisition: Collect data on sloping dryland farmland, including: 10-meter resolution digital elevation model data, 1:50,000 soil type distribution map, land use status map (clearly distinguishing farmland types), and spatial distribution maps of farmland classified as safe for use or strictly controlled by the ecological environment or agricultural and rural departments; the survey found that the main land use type in the area is dryland sloping farmland, planted with corn, and the soil type is red soil. The area is classified as a safe-use area for heavy metals (mainly Cd) in farmland soil.

[0028] S102. Slope Classification: Based on the acquired digital elevation model data, a slope raster layer is generated using a geographic information system. Dryland farmland is divided into three levels according to slope: slope ≤ 6° is gentle slope, slope > 6° and ≤ 25° is medium slope, and slope > 25° is steep slope. A slope classification vector map is generated.

[0029] S103. Generate composite units: Spatially overlay the generated slope classification vector map with the safe utilization type farmland patches. Through intersection operations, the polluted farmland is divided and grouped into several composite units of slope level and pollution category. Each composite unit represents a set of farmland with the same slope characteristics and the same pollution category.

[0030] S104. Preliminary determination of sampling area: 0.2 km² of safe utilization area on a gentle slope. 2 The safe utilization area of ​​the medium slope is 3.5 km². 2 The safe utilization area of ​​the steep slope is 1.3 km².2 ; then calculate the area of each composite unit and its proportion in the total area of the entire contaminated cultivated land; according to the preset total number of sampling regions being 10, perform preliminary allocation based on the area proportion of each composite unit, with 0.4 sampling regions for gentle slopes, 7 sampling regions for moderate slopes, and 2.6 sampling regions for steep slopes; then perform correction to ensure that each pollution category obtains at least 1 sampling region under different slope grades, and increase the sampling weight of moderate slopes, that is, 1 sampling region for gentle slopes, 7 sampling regions for moderate slopes, and 2 sampling regions for steep slopes; S105. Determining the final sampling regions: Cover the target composite unit with 500 m × 500 m regular grids in GIS, randomly select one grid as the starting point, calculate the sampling interval according to the theoretical sampling number of the unit, adopt systematic random sampling combined with field reconnaissance; within the finally selected grids, screen out cultivated land plots with an area greater than 2 mu, clear boundaries, contiguous cultivation and on-site operation conditions, finally determine them as sampling regions, and record their central coordinates and boundary ranges; S2. Determination of sampling points: For the selected sampling regions of different slopes, a differentiated point arrangement method is adopted, which is specifically as follows: Sampling regions of gentle slopes (central radiation and boundary control method): Arrange 1 core sampling point at the geometric center of the region, then extend from the core sampling point along two perpendicular directions to the boundary respectively, and arrange 2 boundary control sampling points each near the plot boundary (about 3 meters away from the boundary); there are 5 sampling points in total in each gentle slope sampling region, and the sampling points of a certain gentle slope sampling region are shown in the attached Figure 1 figure; Sampling regions of moderate slopes ("Feng"-shaped grid point arrangement method): Arrange a main longitudinal section along the maximum slope direction of the slope, divide three slope positions of upslope, midslope and downslope, and set 1 longitudinal core sampling point at each position; take the three core points as the center, arrange horizontal sampling strips along the contour line respectively, with a single horizontal strip length of 20~30 m, corresponding to the typical width of cultivated strips of terraces. Arrange 3 sampling points at equal intervals on each horizontal sampling strip, which are respectively located at the center of the sampling strip, the left side of the sampling strip, and the right side of the sampling strip, to characterize the spatial variation of transverse soil pollution of terraces at the same altitude; at the same time, add 3 auxiliary monitoring points on the longitudinal section of the slope, with a total of 15 sampling points in the complete region, forming the "Feng"-shaped grid point arrangement method. The sampling points of a certain moderate slope sampling region are shown in the attached Figure 2 figure; Steep Slope Sampling Area (Boundary and Early Warning Layout Method): Following the same layout method as for medium slope sampling areas, core sampling points, transverse sampling zone sampling points, and auxiliary monitoring points are established in the steep slope sampling area. Then, through on-site surveys or topographic analysis, all natural channels, fissure zones, or concentrated outflow points that collect water from the steep slope area are identified. Boundary sampling points are established at the boundary where each confluence path leaves the steep slope area and enters a stable area (such as flat land, buffer zones, or ditches), with one boundary sampling point at each boundary. Early warning sampling points are spaced out along the boundary line between the steep slope farmland and the safe area below (such as woodland, roads, or residential areas) as early warning points for whether pollutants are spreading across the boundary. The number of early warning sampling points in each steep slope sampling area is 3 to 5. See the attached list for sampling points in a specific steep slope sampling area. Figure 3 As shown.

[0031] S3. Collection of leachate samples: S301. Remove vegetation debris and other waste from the surface of the sampling point to expose the natural soil surface; S302. Using a stainless steel shovel or a special soil drill, dig a pit vertically downwards at the sampling point with a cross-sectional dimension larger than the initial pit of the infiltration water collector.

[0032] S303. The excavated soil is piled in an orderly manner on the clean bedding material next to the pit according to the natural occurrence layers (such as the topsoil, plow pan, subsoil, etc.), and the depth, color, texture and moisture of each layer are recorded. S304. Set the burial depth of the infiltration collector according to the table below and collect infiltration water. The infiltration collector at each sampling point collects soil lateral flow infiltration water and soil vertical flow infiltration water. The lateral flow infiltration water and vertical flow infiltration water are stored independently. Burial Depth Table

[0033] During the high-water season, normal-water season, and low-water season, the above sample collection operation is repeated. Each time a sample is taken, the liquid in the second storage tank 2 must be completely extracted. During the entire one-year monitoring cycle, there is no need to excavate the soil again. Example 2

[0034] As attached Figures 4-5As shown, this embodiment of the differentiated sampling method for groundwater infiltration in dry land based on slope grading is based on Embodiment 1. The difference between Embodiment 1 and Embodiment 1 is that the infiltration collector includes a first storage tank 1, a second storage tank 2, and a pump 3. The first storage tank 1 is a square tank (internal dimensions: 30cm × 30cm × 40cm), and the second storage tank 2 is a cylindrical tank (internal dimensions: diameter 25cm, height 50cm). The bottoms of the first storage tank 1 and the second storage tank 2 are connected by a pipe, and the horizontal position of the bottom of the first storage tank 1 is 20cm higher than the horizontal position of the bottom of the second storage tank 2. The first storage tank 1 has an inlet, and the inlet is provided with perforated partitions from the inside to the outside. The system consists of a plate 4 (a perforated rigid PVC plate with a pore size of 5mm, a pore spacing of 15mm, and a thickness of 5mm), a filter membrane layer 5 (PVDF with a pore size of 0.45μm), a river sand layer 6 (acid-washed quartz sand with a particle size of 0.5~1.0mm), and a filter cotton layer 7 (3cm thick polyester fiber non-woven fabric). The filter cotton layer 7 covers the inlet of the first liquid storage tank 1. The second liquid storage tank 2 has an insertion port at the top, and a guide sleeve 8 is provided on the insertion port. The liquid extractor 3 is inserted into the second liquid storage tank 2 from top to bottom through the guide sleeve 8. The liquid extraction head 9 of the liquid extractor 3 is equipped with a one-way valve 10. The first liquid storage tank 1 and the second liquid storage tank 2 are both buried in the soil layer 11, and the upper part of the guide sleeve 8 and the upper part of the liquid extractor 3 are located above the soil layer 11. Two types of infiltration collectors are set up at each sampling point: one type has the inlet of the first storage tank 1 located at the top of the first storage tank 1 to collect vertical infiltration water from the soil, and the other type has the inlet located on the side of the first storage tank 1 to collect lateral infiltration water from the soil. After the device is installed, under natural rainfall conditions, rainwater infiltrates, is filtered, and enters the first storage tank 1, then flows by gravity to the second storage tank 2 for storage. Forty-eight hours after an effective rainfall event (>15mm), the first sampling is conducted. The pump 3 is operated; once it is full, it is removed, and the piston is pressed down to discharge the water sample into a sampling bottle. After sampling, the sampling time, water sample volume, and on-site weather conditions are recorded.

Claims

1. A method for differentiated sampling of groundwater infiltration in dry land based on slope grading, characterized in that... Includes the following steps: S1. Sampling area determination: S101. Data Acquisition: Collect data on sloping dryland farmland, including: digital elevation model data, soil type distribution map, land use status map, and spatial distribution map of polluted farmland. S102. Slope Classification: Based on the acquired digital elevation model data, a slope raster layer is generated using a geographic information system; dry farmland is divided into three levels according to slope: gentle slope, medium slope, and steep slope, and a slope classification vector map is generated. S103. Generate composite units: Perform spatial overlay analysis between the generated slope classification vector map and the spatial distribution map of polluted farmland. Through intersection operation, divide and group the polluted farmland into several composite units with slope grades and pollution categories. Each composite unit represents a set of farmland with the same slope characteristics and the same pollution category. S104. Preliminary determination of sampling areas: Calculate the area of ​​each composite unit and its proportion to the total area of ​​the polluted farmland; based on the preset total number of sampling areas, make preliminary allocations according to the area proportion of each composite unit, and calculate the initial theoretical sampling number of each unit; then make corrections to ensure that at least one sampling area is obtained for each pollution category under different slope levels; for medium slope areas, increase the sampling weight for plots located in the middle and lower part of the slope, near ditches or residential areas; S105. Determine the final sampling area: Cover the target composite unit with a regular grid, randomly select a grid as the starting point, calculate the sampling interval according to the theoretical sampling number of the unit, and systematically select grids; within the finally selected grids, select farmland plots with an area greater than 2 mu, clear boundaries, contiguous cultivation, and on-site operation conditions, and finally determine them as the sampling area, and record their center coordinates and boundary range. S2. Sampling point determination: Sampling area on gentle slopes: A core sampling point is set up at the geometric center of the area, and then a boundary control sampling point is set up near the boundary in at least two directions from the core sampling point. Sampling area on medium slope: Establish a main longitudinal profile along the direction of maximum slope. Set up core sampling points longitudinally at the upper, middle and lower slope positions of the main longitudinal profile. Then set up transverse sampling zones along the contour lines with each core sampling point as the center. Set up at least 3 sampling points on each transverse sampling zone to capture transverse variation. At the same time, add 3 auxiliary monitoring points on the longitudinal profile of the slope. Steep slope sampling area: First, follow the same sampling method as the medium slope sampling area to set up core sampling points, transverse sampling points, and auxiliary monitoring points. Then, through on-site surveys or topographic analysis, identify all natural channels, fissure zones, or concentrated outflow points that collect water from the steep slope area. Set up boundary sampling points at the junction of each confluence path that is about to leave the steep slope area and enter the stable area. On the boundary line between the steep slope farmland and the safe area below, set up early warning sampling points at intervals as early warning points for whether pollutants have crossed the boundary and spread. S3. Collection of leachate samples: S301. Remove vegetation debris and other waste from the surface of the sampling point to expose the natural soil surface; S302. Excavate a pit with a cross-sectional dimension larger than the initial pit of the infiltration water collector at the marked point; S303. The excavated soil is piled up in an orderly manner next to the pit according to the natural occurrence layers, and the depth, color, texture and moisture of each layer are recorded. S304. Set the burial depth of the leachate collector according to Table 1 and collect leachate; Table 1 Burial Depth Table 。 2. The method for differentiated sampling of groundwater infiltration in dry land based on slope grading as described in claim 1, characterized in that... The slope of the gentle slope is ≤6°, the slope of the medium slope is >6° and ≤25°, and the slope of the steep slope is >25°.

3. The method for differentiated sampling of groundwater infiltration in dry land based on slope grading as described in claim 1, characterized in that... In step S2: For the sampling area on a gentle slope: starting from the core sampling point, extend towards the boundary in two perpendicular directions, and set up two boundary control sampling points near the boundary of the plot; a total of 5 sampling points are set up in each gentle slope sampling area; For medium-slope sampling areas: there are 3 sampling points in each transverse sampling zone. On each transverse sampling zone, 3 points are arranged at equal intervals, located at the center of the transverse sampling zone, the left side of the transverse sampling zone, and the right side of the transverse sampling zone, respectively; there are a total of 15 sampling points in each medium-slope sampling area. For steep slope sampling areas: the number of boundary sampling points at each intersection is 1, and the number of warning sampling points in each steep slope sampling area is 3 to 5.

4. The method for differentiated sampling of groundwater infiltration in dry land based on slope grading as described in claim 1, characterized in that... The infiltration collector at each sampling point collects soil lateral infiltration and soil vertical infiltration, and the lateral and vertical infiltration are stored independently.

5. The method for differentially distributed groundwater sampling in dry land based on slope grading as described in claim 1 or 4, characterized in that... The leachate collector includes a first storage tank (1), a second storage tank (2), and a pump (3). The first storage tank (1) is a square tank, and the second storage tank (2) is a cylindrical tank. The bottom of the first storage tank (1) and the bottom of the second storage tank (2) are connected by a pipe, and the bottom of the first storage tank (1) is at a higher horizontal position than the bottom of the second storage tank (2). The first storage tank (1) has an inlet, and from the inside out, a perforated partition (4), a filter membrane layer (5), and a river sand layer are arranged sequentially. (6) and filter cotton layer (7), and filter cotton layer (7) covers the water inlet of the first liquid storage tank (1). The second liquid storage tank (2) has an insertion port at the top, and a guide sleeve (8) is provided on the insertion port. The pump (3) is inserted into the second liquid storage tank (2) from top to bottom through the guide sleeve (8). The pump head (9) of the pump (3) is provided with a one-way valve (10). The first liquid storage tank (1) and the second liquid storage tank (2) are both buried in the soil layer (11), and the upper part of the guide sleeve (8) and the upper part of the pump (3) are located above the soil layer (11).

6. The method for differentiated sampling of groundwater infiltration in dry land based on slope grading as described in claim 5, characterized in that... The inlet of the first liquid storage tank (1) is located on the top or side of the first liquid storage tank (1).

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