Dynamic analysis method for sediment source of small watershed

Abstract

The invention relates to the technical field of environment detection, in particular to a small watershed sediment source dynamic analysis method, which comprises the following steps of: 1, selecting a research object, screening a small watershed as a research area in a loess hilly area, and needing to contain long-series rainfall, runoff and sediment observation data; the method comprises the following steps: determining slopes and small watersheds of cultivated land, forest land, grassland and land-abdicating slopes as research objects; during the application period of the technical scheme, through the sampling mechanism integrating adjustment, transmission and displacement modules, multi-depth soil samples can be synchronously collected, the drilling depth can be accurately controlled to reduce soil disturbance, repeated drilling is not needed, the device can adapt to small-watershed complex terrains, and the problems that existing equipment can only take deepest samples and is low in precision are solved; the method is highly adaptive to nuclide measurement and fingerprint identification methods, sampling efficiency and data accuracy are greatly improved, and reliable support is provided for small watershed sediment source analysis and water and soil conservation measure optimization.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of environmental detection, in particular to a small watershed sediment source dynamic analysis method. BACKGROUND

[0002] The loess hilly region is a high-incidence area of water and soil loss. The loess in the region is deep, the surface is broken, and the gullies are crisscrossed, which is an important source of watershed sediment. For a long time, due to the influence of human activities, the land use types such as slope farmland in the region have been converted to forest land and grassland, and the underlying surface conditions have changed significantly, resulting in changes in the contribution of different land use types to watershed erosion sediment yield. Although the increase in forest area and the popularization of soil and water conservation measures have reduced the annual average sediment yield modulus of the watershed, the soil erosion intensity under partial rainfall in some regions is still high. Due to the short time of existing observation sites and the limited data series, it is difficult to accurately reveal the historical changes of erosion sediment yield intensity of different land use types and to clearly illustrate the specific contribution of each land use type to watershed sediment yield, which hinders the control of water and soil loss.

[0003] Currently, the research on small watershed erosion sediment yield and sediment source in the region mainly relies on traditional methods such as remote sensing image interpretation and comparison observation of different types of runoff plots. These methods have obvious limitations: remote sensing image interpretation can only obtain the static changes of land use types at different times and cannot realize the direct comparison of erosion intensity before and after the conversion of the same land use type; runoff plot observation is limited by spatial scale and cannot reflect the overall erosion process under the complex hydrological connectivity of the small watershed. In addition, the sediment yield monitored at the outlet of the watershed only represents part of the erosion amount and cannot fully explain the soil erosion mechanism of different land use types in the watershed. In terms of soil sampling equipment, a soil sampler with sampling depth adjustment function is disclosed in Chinese Patent No. CN218512064U, which includes a sampler body, a handle, a main rod, a secondary rod, a rotating drum, and a primary soil loosening tooth. The sampling depth is adjusted through the components such as the adapter block, the elastic clamping foot, and the clamping slot, which solves the problem of data deviation caused by insufficient depth of the traditional sampler.

[0004] However, this device can only obtain soil samples at the deepest position of the drilling path and cannot simultaneously collect soil samples at different depths in a single drilling. It also lacks a structure for quickly and independently collecting samples at different depths, making it difficult to meet the needs of precise measurement of indicators such as the distribution of different depth soil layers and particle composition in small watershed research, further restricting the accuracy of erosion rate calculation and sediment source analysis. At the same time, due to the strong spatial differentiation of erosion type and intensity in the loess hilly region, the mutual feedback between environmental change and erosion sediment yield is complex. The limitations of traditional methods and existing sampling equipment make it difficult to accurately carry out quantitative analysis of sediment sources and evaluation of the erosion reduction benefits of soil and water conservation measures.

[0005] While radioisotope tracing technology has been applied in soil erosion research, existing studies often use only one type of isotope, failing to fully utilize the complementarity of different isotopes over different research periods. This makes it difficult to achieve accurate comparisons of erosion rates before and after land use changes. Furthermore, studies on sediment deposited by silt-retaining dams often fail to systematically combine sedimentary cycle division, historical precipitation data, and isotope dating, making it impossible to fully reconstruct the dynamic evolution of sediment yield in small watersheds or reveal the impact of underlying surface changes on sediment sources. Therefore, there is an urgent need for a method that can integrate multiple technologies, adapt to the need for precise sampling, and achieve dynamic analysis of sediment sources in small watersheds, providing a scientific basis for optimizing soil and water conservation measures and comprehensive management of soil erosion. Summary of the Invention

[0006] To improve the convenience of sampling during the application of existing technologies, this application provides a method for dynamic analysis of sediment sources in small watersheds.

[0007] This application provides a method for dynamic analysis of sediment sources in small watersheds, which adopts the following technical solution and includes the following steps:

[0008] Step 1: Selection of research subjects. Within the Loess Hilly Region, small watersheds are selected as the study area, requiring long-term data on rainfall, runoff, and sediment. The slopes and small watersheds of cultivated land, forest land, grassland, and reclaimed farmland are identified as the research subjects.

[0009] Step 2: Conduct field investigations to collect data on topography, precipitation, runoff, sediment, land use, and soil and water conservation records for the study area; investigate the parameters of the Menhulu Dam, land use distribution and historical changes, and vegetation restoration after farmland conversion; use drones to acquire images and combine them with remote sensing to interpret land use changes in the small watershed.

[0010] Step 3: Soil sampling at reference points. Select non-eroded flat land or old terraces as reference points. After setting up the points, use sampling equipment to collect full profile and layered soil samples, and label the sampling information.

[0011] Step 4: Reference point sample processing. After the soil sample is naturally air-dried, it is ground, sieved to remove impurities, sealed and placed before being sent for testing of 137Cs and 210Pbex activities, and the data is recorded.

[0012] Step 5: Determine the background nuclide and sedimentation flux. Organize the nuclide data of the reference point, combine it with geographical and precipitation data to calculate the infiltration coefficient, and determine the background nuclide value and 210Pbex sedimentation flux;

[0013] Step Six: Slope soil sampling. The land is divided into disturbed and undisturbed land. Disturbed land mainly consists of slopes that have been converted from farmland, while undisturbed land includes woodland, grassland, and wasteland. Sampling points are selected on the slope, and sampling equipment is used to take samples at different depths based on soil thickness. Sampling information is then marked.

[0014] Step 7: Slope sample preparation. Prepare slope soil samples according to Step 4, send them for nuclide activity testing, and record the data.

[0015] Step 8: Sampling of sediment at the silt-retaining dam. Select the sampling point at the silt-retaining dam, excavate the sediment profile, identify the sedimentary cycles, and then sample in layers, measure the thickness and label the information.

[0016] Step Nine: Determine the time of sedimentation layers, adjust precipitation data to find the time of major floods, check dam records to confirm key nodes; measure the 137Cs activity of sedimentation layers to determine the time of sedimentation layers such as the year of dam construction and before and after land reclamation;

[0017] Step 10: Source analysis. The dam-controlled area is designated as the source area. Samples are taken to measure fingerprint factors such as soil particle composition, soil nutrients, and radionuclide activity values. The contribution rate is calculated and compared before and after the land conversion, and the changes in sediment sources are analyzed.

[0018] Optionally, the sampling device includes a movable base, a vertical plate is fixedly installed on the top of the movable base, a displacement mechanism is fixedly installed on the front of the vertical plate, and a sampling mechanism is fixedly installed on the moving end of the displacement mechanism.

[0019] The sampling mechanism includes a mounting base, which is fixedly mounted on the moving end of the displacement mechanism. A first motor is fixedly mounted on the top of the mounting base, and a main mounting frame is fixedly mounted on the output end of the first motor. An adjustment module is fixedly mounted on the inner side of the main mounting frame, and a drilling cylinder is fixedly mounted on the bottom of the main mounting frame. A drilling thread head is fixedly mounted on the bottom of the drilling cylinder. Sampling modules are movably mounted on both sides of the inside of the drilling cylinder at equal intervals in a linear arrangement. A transmission module is movably mounted inside the drilling cylinder. The top of the transmission module is connected to the bottom of the adjustment module, and the transmission module and the sampling module are connected by a transmission.

[0020] Optionally, the mobile base includes a base, the upright plate is fixedly installed on the top side of the base, and universal wheel frames are rotatably connected to the four corners of the bottom of the upright plate. Universal wheel bodies are rotatably connected to the bottom of the universal wheel frames. A chassis is fixedly installed on the top of the base. A battery is installed inside the chassis, and a controller is located in the middle of the top of the chassis.

[0021] Optionally, the upright plate is fixedly installed with support frames at both ends on the side away from the displacement mechanism. The bottom of the support frame is fixedly connected to the top of the base. The outer surface corners of the base, support frame and upright plate are all set to be arc-shaped.

[0022] Optionally, a connecting frame is fixedly installed on the upper outer side of the support frame, a handrail frame is fixedly installed on the outer end of the connecting frame, and an anti-slip handrail glove is fixedly installed on the outer side of the handrail frame.

[0023] Optionally, the displacement mechanism includes a vertical rail, which is bolted to the side of the upright plate away from the handrail. A first lead screw is rotatably connected inside the vertical rail. A third motor is fixedly installed on the top of the vertical rail. The output end of the third motor is fixedly connected to the top of the first lead screw via a coupling. A slider is threadedly connected to the outer surface of the first lead screw. The slider is slidably connected inside the vertical rail. The mounting base is fixedly installed on the end of the slider away from the upright plate.

[0024] Optionally, the adjustment module includes a fixed plate, which is fixedly installed inside the upper part of the mounting frame. A second motor is fixedly installed on the top of the fixed plate, and a second lead screw is fixedly installed on the bottom of the fixed plate. The second lead screw is rotatably connected to the bottom of the fixed plate, and the top of the second lead screw is connected to the output end of the second motor through a coupling. A sliding frame is threadedly connected to the outer surface of the second lead screw. A sliding frame is fixedly installed on the bottom of the fixed plate, and the sliding frame is slidably connected to the inner side of the sliding frame. The bottom of the sliding frame is connected to the top of the transmission module.

[0025] Optionally, the sampling module includes a receiving hole and an inner rail frame. The receiving holes are linearly arranged at equal intervals on both sides of the drilling cylinder. The inner rail frames are linearly arranged at equal intervals and fixedly installed on both sides of the inside of the drilling cylinder. The inner rail frames are all located inside the receiving holes. A movable plate is slidably connected inside the inner rail frame. A sampling component is fixedly installed on the outside of the movable plate. The sampling component is slidably connected inside the receiving hole. The inside of the movable plate is connected to the transmission module.

[0026] Optionally, the transmission module includes a side sliding groove and a sliding rod. The side sliding groove is arranged in a ring at equal intervals inside the drill barrel. The sliding rod is slidably connected to the inner side of the side sliding groove. Both sides of the sliding rod are provided with strip-shaped grooves. An inner hinge seat is fixedly installed in a linear arrangement at equal intervals on the inner side of the strip-shaped groove. A linkage frame is hinged to the inner side of the inner hinge seat. Side plates are fixedly installed at both ends of the outer side of the linkage frame. The inner side of the side plate is rotatably connected to the middle of both sides of the movable plate.

[0027] Optionally, the sampling assembly includes a connecting rod, which is fixedly installed on the outer middle of the movable plate. A fixing seat is fixedly installed on the outer end of the connecting rod. A sampling block is fixedly installed on the outer side of the fixing seat. A sampling guide cone is fixedly installed on the outer side of the sampling block. Sampling grooves are evenly spaced and arranged in a ring on the outer surface of the sampling block. The drilling thread head is also generally conical.

[0028] In summary, this application includes the following beneficial technical effects:

[0029] 1. During the application of this technical solution, the sampling mechanism, which integrates the adjustment module, transmission module, and sampling module, enables the simultaneous collection of soil samples at multiple depths within the drilling path according to different sampling scenarios. Layered soil samples can be obtained without repeatedly inserting and removing the drilling tube. In addition, combined with the layered sampling requirements for different land use types such as reference points and slopes, the method can quickly match the sampling needs of 1cm or 2cm layers, greatly reducing the number of field sampling operations. This achieves the effect of efficiently obtaining samples at multiple depths in a single sampling, solving the problem that existing soil sampling equipment can only obtain samples at the deepest position of the drilling path, and data deviation is easily caused by point offset in multiple samplings. Furthermore, the method and sampling mechanism of this technical solution are highly adaptable. When handling sampling of different land use types such as cultivated land, forest land, and converted slope land, there is no need to frequently change equipment parts. The requirements can be met by adjusting the mechanism alone, further reducing the complexity of manual operation and improving the continuity and efficiency of field sampling.

[0030] 2. During the application of this technical solution, the sampling mechanism, equipped with a displacement mechanism, allows for precise control of the drilling depth of the drilling tube and the timing of the sampling component's extension. This enables simultaneous sampling, simultaneous scraping of samples, and rapid collection and preservation, avoiding excessive soil disturbance during sampling and ensuring the original state of the stratified samples. Furthermore, considering the sampling accuracy requirements for different scenarios such as silt-dam sedimentary profiles and source area regions, the solution can stably obtain samples that meet the standards for nuclide measurement and fingerprint identification analysis, thereby improving the quality and accuracy of stratified samples. This solves the problems of low depth control accuracy and susceptibility to sample disturbance in traditional sampling equipment, leading to poor reliability of subsequent analysis data. In addition, the method of this technical solution, through the cooperation of the sampling mechanism with UAV image interpretation and field surveys, can accurately locate sampling points and quickly complete stratified sampling, avoiding the impact of human error on sample representativeness. This provides a high-quality data foundation for subsequent steps such as determining background values ​​of nuclides and calculating source contribution rates, further improving the accuracy of the entire sediment source analysis process.

[0031] 3. During the application of this technical solution, the sampling mechanism, equipped with a mobile base and an independent power supply box, allows for flexible movement within the complex terrain of small watersheds in the Loess Hilly Area. Sampling work can be carried out without relying on an external power source. Furthermore, by incorporating multiple sampling points, reference points, slopes, silt-retaining dams, and other survey requirements, the sampling scene can be quickly switched, thus achieving the effect of adapting the equipment to complex field environments. This solves the problems of traditional sampling equipment being inconvenient to move, relying on fixed power sources, and being difficult to adapt to multiple sampling scenarios in small watersheds. In addition, the method of this technical solution, through the combination of radionuclide measurement and composite fingerprint recognition, fully utilizes the precise stratified samples obtained by the sampling mechanism to reveal the erosion and sediment yield patterns of different land use types. Compared with traditional methods, this approach is more systematic, providing a scientific basis for the optimized configuration of soil and water conservation measures and further enhancing the targeted nature of soil and water conservation in small watersheds. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure in an embodiment of this application;

[0033] Figure 2 This is a schematic diagram of the rear view structure in an embodiment of this application;

[0034] Figure 3 This is a bottom-view structural diagram of an embodiment of this application;

[0035] Figure 4 This is a front view schematic diagram of the sampling mechanism in its extended state in an embodiment of this application;

[0036] Figure 5 This is a side view of the sampling mechanism in its extended state in an embodiment of this application;

[0037] Figure 6 This is a schematic diagram of the sampling module in the extended state of the sampling mechanism in the embodiments of this application;

[0038] Figure 7 This is a schematic diagram of the internal structure of the drill barrel in an embodiment of this application;

[0039] Figure 8 This is a schematic diagram of the sampling module structure in an embodiment of this application;

[0040] Figure 9 This is an embodiment of the present application. Figure 3 A magnified structural diagram at point A;

[0041] Figure 10 This is an embodiment of the present application. Figure 7 A magnified structural diagram at point B;

[0042] Figure 11 This is an embodiment of the present application. Figure 8 A magnified structural diagram at point C.

[0043] Reference numerals: 1. Movable seat; 11. Base; 12. Caster wheel frame; 13. Caster wheel body; 14. Chassis; 15. Connecting frame; 2. Vertical plate; 3. Displacement mechanism; 31. Vertical rail; 32. First lead screw; 33. Third motor; 34. Slider; 4. Handrail frame; 5. Support frame; 6. Sampling mechanism; 61. Mounting seat; 62. First motor; 63. Main mounting frame; 64. Adjustment module; 641. Fixed plate; 642. Second motor; 643. Second lead screw; 644. Sliding plate 645. Frame; 65. Slide; 66. Drilling cylinder; 67. Drilling thread head; 67. Sampling module; 671. Storage hole; 672. Inner rail frame; 673. Movable plate; 674. Sampling assembly; 6741. Connecting rod; 6742. Fixed seat; 6743. Sampling block; 6744. Sampling guide cone; 6745. Sampling groove; 68. Transmission module; 681. Side slide groove; 682. Sliding rod; 683. Strip groove; 684. Inner hinge seat; 685. Linkage frame; 686. Side plate. Detailed Implementation

[0044] The following is in conjunction with the appendix Figures 1-11 This application will be described in further detail.

[0045] This application discloses a method for dynamic analysis of sediment sources in small watersheds. For example... Figures 1-11 As shown, it includes the following steps:

[0046] Step 1: Selection of research subjects. Typical small watersheds in the Loess Plateau of western Henan Province will be selected as the research area. Specifically, the Hugou small watershed in Song County will be selected. It needs to be typical and representative in terms of landform type and sediment yield characteristics. Within this research area, areas with long-term observation data of rainfall, runoff and sediment will be selected. The long-term observation data will cover 20-25 years. Slopes and small watersheds of different land use types will be identified as research subjects. Land use types include cultivated land, forest land, grassland and reclaimed farmland slopes to ensure that the research subjects can reflect the core characteristics of regional soil and water loss.

[0047] Step Two: Field investigation, collecting topographic data, geomorphological survey reports, multi-year precipitation observation data, runoff observation data, sediment observation data, land use type data, soil and water conservation measures data, and relevant historical data for the study area. Topographic data includes DEM (Digital Elevation Model). Data, contour maps, multi-year precipitation observation data including monthly precipitation, daily precipitation, and rainstorm event records; runoff observation data including runoff volume and runoff coefficient; sediment observation data including sediment transport and sediment concentration; land use type data including land use maps from different years; relevant historical data including soil and water conservation project archives; field investigation of the construction time, controlled area, siltation area, records of dam collapse, and operation and scheduling of the Menhulu Dam within the watershed; investigation of the spatial distribution range and historical change trajectory of different land use types, including the time nodes of conversion of cultivated land to forest land; investigation of land use patterns, vegetation restoration types, and restoration degree after the conversion of sloping cultivated land to grassland or forest land; vegetation restoration types including trees, shrubs, and herbs; restoration degree as vegetation cover; high-resolution imagery of the underlying surface of the small watershed was acquired using a DJI Matrice M300RTK drone with an image resolution of 0.08-0.12 meters; the boundaries of different land use patterns and landform types were corrected through field verification, combined with 1990 data. Historical remote sensing images from 2000 to interpret the land use change process in small watersheds provide basic data for subsequent sampling point layout and analysis of erosion and sediment yield genesis.

[0048] Step 3: Soil sampling at reference points. Select reference points within the study area. Reference points should be flat land with slight erosion since the 1960s or old terraces built before the 1960s that have remained undisturbed for a long time. This will reduce the error of the background value and ensure the accuracy of subsequent calculations. There should be 3-5 reference points. For each reference point, a network method should be used to set up sampling points with a grid spacing of 4-6 meters × 4-6 meters. There should be no less than 12 sampling points at each reference point to ensure the representativeness of the samples. Use a soil drill to take soil samples at a depth of 0-30 cm. Collect full profile soil samples and layered soil samples. For full profile soil samples, a complete soil column of 0-30 cm should be taken at once. For layered soil samples, samples should be taken from the ground surface downwards in 1 cm layers. Place the full profile samples and layered samples from each sampling point into a special sample bag and label it with the reference point number, sampling location, sampling depth, and sampling date.

[0049] Step 4: Reference point sample processing. Place the collected reference point soil samples in a well-ventilated and dry room to air dry naturally. Avoid direct sunlight and high-temperature baking during the air drying process. After air drying, grind the soil samples with a grinder and then pass them through a soil sieve with a 1mm aperture to remove grass roots and stones. Weigh 380-420g from the processed soil sample, usually about 400g, and put it into a special sealed sample box. After sealing, place it for 1 month. Send the sealed soil sample to the Key Laboratory of Soil and Water Conservation of Loess Plateau of the Ministry of Water Resources. Use the American ORTEC low background gamma spectrometer GMX-50P4 and its matching analysis software to measure the activity values ​​of 137Cs and 210Pbex in the soil sample. The measurement time for each soil sample is 24-30 hours. Record the measurement data. The data will be used for subsequent calculation of nuclide background values ​​and acquisition of erosion rate model parameters.

[0050] Step 5: Determining Nuclide Background and Sedimentation Flux. Data on the 137Cs and 210Pbex activities of soil samples at different depths at various reference points were compiled. The trends of their activities with depth in the soil profile were analyzed, and compared with relevant research results from the same latitude region and the Loess Plateau region to verify the data's rationality. Geographic latitude data and multi-year average precipitation data for the study area were collected. Geographic latitude data were obtained through GPS positioning, and multi-year average precipitation data were retrieved from local meteorological stations. Combined with the total activities of 137Cs and 210Pbex in the soil samples at the reference points, the infiltration coefficients of these two elements in the soil of the study area were calculated, providing core parameters for the 137Cs erosion rate calculation model and the unsteady-state 210Pbex erosion rate calculation model. The background values ​​of 137Cs and 210Pbex in the study area were determined through statistical analysis of the 137Cs and 210Pbex activities at each reference point. The 210Pbex activity was calculated based on the total activity of 210Pbex and the depositional age of the soil profiles at the reference points. The average annual subsidence flux supports the estimation of short-term erosion rate after farmland is converted to forest.

[0051] Step Six: Slope Soil Sampling. The land use types in the study area are divided into disturbed and undisturbed land. Disturbed land mainly consists of converted farmland slopes, while undisturbed land includes woodland, grassland, and wasteland. Representative slopes are selected for both disturbed and undisturbed land. Sampling points are laid out on each slope using a network method, with a grid spacing of 3-5 meters × 3-5 meters. Each plot has at least 12 sampling points. Soil augers are used for sampling. The sampling depth is determined based on soil thickness: 0-20 cm in areas with normal soil thickness and 0-30 cm in areas with thicker soil. Full-profile soil samples and stratified soil samples are collected. Full-profile soil samples are taken as a single, complete soil column at the corresponding depth. Stratified soil samples are collected in 1 cm increments from the top 0-5 cm layer, as the surface soil disturbance after conversion to farmland is minimal, and erosion and 210Pbex new subsidence mainly occur here. Samples below 5 cm are collected in 2 cm increments. For stratified unit collection, soil samples from each sampling point were placed in a special sample bag and labeled with the land use type, slope number, sampling location, sampling depth and sampling date;

[0052] Step 7: Slope Sample Processing. Following the soil sample processing method described in Step 4, process the collected disturbed and undisturbed slope soil samples. The process includes air drying, grinding, sieving, and impurity removal. Use a 1mm sieve. Weigh 380-420g (approximately 400g) from each processed soil sample, place it in a special sealed sample box, seal it, and store it for one month. Then, send the sealed soil samples to the Key Laboratory of Soil and Water Conservation of the Loess Plateau, Ministry of Water Resources. Use an ORTEC GMX-50P4 low-background gamma spectrometer and accompanying analysis software to measure the activity values ​​of 137Cs and 210Pbex in the soil samples. The measurement time for each soil sample is 24-30 hours. Record the measurement data. This data will be used for subsequent estimation of the multi-year average erosion rate based on the 137Cs decay formula to restore the initial activity value before land conversion and on the calculation of the increased settlement and decay of 210Pbex after land conversion.

[0053] Step 8: Sampling of sediments from the silt-retaining dam. Select sampling locations within the chosen silt-retaining dam within the study area, ensuring the sampling locations are 5-7 meters away from the dam body and the slopes on both sides to avoid interference from the dam body and slopes. Use an excavator to excavate the sedimentary profile of the silt-retaining dam to a depth of 3-5 meters. Based on the characteristics of heavy rainfall and high sand yield in the Loess Plateau and the sorting of sediment deposition, coarse particles are first deposited as sand, followed by silt, and finally clay. Identify sedimentary cycles by observing the alternating distribution of clay, silt, and sand layers in the sedimentary profile. Use a stainless steel shovel for each sedimentary cycle to avoid sample contamination. Sampling is performed at different depths. When the cycle thickness is less than 10 cm, sample from two layers (upper and lower); when the cycle thickness is greater than 10 cm, sample from three layers. Layer sampling is conducted, divided into upper, middle and lower layers. The average thickness of each sedimentary layer is measured using a measuring tape. The location, thickness and sampling details of each sedimentary layer are recorded. The collected sedimentary soil samples are placed in special sample bags and labeled with the silt-retaining dam number, sampling location, sedimentary layer depth and sampling date.

[0054] Step Nine: Defining the Sedimentary Layer Time. Historical precipitation data for the study area was retrieved from local meteorological stations to screen for the occurrence time of major flood events. The criterion for major flood events is daily precipitation greater than 50 mm. Considering the characteristics of heavy rainfall and high sediment yield in the Loess Plateau, such events correspond to obvious sedimentary cycles. The engineering archives of the silt-retaining dam were reviewed to confirm the dam's construction year and key time nodes during its operation. Key time nodes include maintenance and reinforcement times. The collected sedimentary soil samples from the silt-retaining dam were processed using the method in Step Four, and the 137Cs activity value was measured to identify the sedimentary layer corresponding to the peak 137Cs activity value. This layer corresponds to the peak 137Cs settlement year in 1963, providing a key time anchor for the sedimentary dating of the silt-retaining dam. Combining historical precipitation data, dam construction year, and peak 137Cs activity value, the construction year, major flood year, and 137Cs activity value of the silt-retaining dam were defined. Sedimentary layers before and after the peak year of subsidence and before and after the land conversion policy were recorded, with the time points before and after the land conversion policy being based on the year of implementation of the local land conversion policy. This provides a time scale for comparing the erosion and sediment yield rates of different historical periods in the subsequent small watershed.

[0055] Step 10: Lot Analysis. Based on the land use type of the small watershed, the dam-controlled area is divided into 3-4 lot type zones, including converted grassland, cultivated land, forest land, and barren slopes. According to the compiled land use distribution map of the small watershed, sampling points are determined in each plot within each lot type zone using a random number table method. Each plot should have at least 12 sampling points. After removing surface debris with a stainless steel shovel, topsoil samples (0-5cm depth) are collected using sampling equipment. Each sampling point should yield a soil sample weighing 480-520g. All topsoil samples from the same plot are mixed and thoroughly stirred in a clean container for 4-6 minutes. The required weight of soil sample is then collected using the quartering method. The soil sample is flattened into a circle, divided into four parts by drawing a cross, and two diagonal parts are taken. The required soil sample weight is 950-1050g. Finally, 3-4 soil samples are retained from each plot, especially plots larger than 100 square meters. For every additional 50 mu (approximately 3.3 hectares) of land use, one additional soil sample was taken. Fingerprint identification factors were measured on surface soil samples from the source area and on soil samples from each sedimentary layer of the silt-retaining dam. These factors included soil particle composition, soil nutrients, and radionuclide activity values. Soil particle composition included the content of sand, silt, and clay particles; soil nutrients included organic matter, nitrogen, and phosphorus content; and radionuclides included 137Cs and 210Pbex. A composite fingerprint identification method was used to screen effective fingerprint identification factors, eliminating factors with high correlation and weak discriminative ability. A linear mixture model was established to calculate the relative contribution rate of different source areas to the sediment deposition of the silt-retaining dam during secondary floods. Different source areas represent different land use types. Comparisons were made between 20 years before and 20 years after land conversion. This study analyzes the contribution rate data of various sediment source types in different years, examines the changing characteristics of sediment sources in small watersheds, quantitatively assesses the effectiveness of the Grain for Green project based on the analysis results, determines the threshold for vegetation coverage construction in small watersheds, and proposes an optimized configuration model for soil and water conservation measures in small watersheds. This provides technical support for the high-quality development of ecological environmental protection and soil and water conservation in small watersheds in the Loess Hilly Area of ​​western Henan.

[0056] Please refer to Figures 1-11 The sampling device includes a movable base 1, a vertical plate 2 is fixedly installed on the top of the movable base 1, a displacement mechanism 3 is fixedly installed on the front of the vertical plate 2, and a sampling mechanism 6 is fixedly installed on the moving end of the displacement mechanism 3.

[0057] The sampling mechanism 6 includes a mounting base 61, which is fixedly mounted on the moving end of the displacement mechanism 3. A first motor 62 is fixedly mounted on the top of the mounting base 61, and a main mounting frame 63 is fixedly mounted on the output end of the first motor 62. An adjustment module 64 is fixedly mounted on the inner side of the main mounting frame 63. A drilling cylinder 65 is fixedly mounted on the bottom of the main mounting frame 63, and a drilling thread head 66 is fixedly mounted on the bottom of the drilling cylinder 65. Sampling modules 67 are movably mounted on both sides of the drilling cylinder 65 at equal intervals. A transmission module 68 is movably mounted inside the drilling cylinder 65. The top of the transmission module 68 is connected to the bottom of the adjustment module 64, and the transmission module 68 and the sampling module 67 are connected by a transmission. During the application of this device, the cooperation between the moving base 1, the upright plate 2, the displacement mechanism 3, and the sampling mechanism 6 allows the sampling machine to be adjusted first by means of the displacement mechanism 3. The position of the sampling mechanism 6 is determined by the moving end of the displacement mechanism 3, which drives the sampling mechanism 6 to move. When the sampling mechanism 6 is working, the first motor 62 at the top of the mounting base 61 drives the main mounting frame 63 to rotate, and the drilling cylinder 65 at the bottom of the main mounting frame 63 rotates accordingly. The drilling thread head 66 at the bottom of the drilling cylinder 65 can assist the drilling cylinder 65 to drill into the target area more smoothly. At the same time, the adjustment module 64 inside the main mounting frame 63 drives the transmission module 68 inside the drilling cylinder 65 to move. The transmission module 68 then links the sampling modules 67 on both sides inside the drilling cylinder 65 to perform sampling actions. This design makes the position adjustment more flexible and the drilling operation more convenient during the sampling process. The sampling module 67 can accurately cooperate to complete the sampling, effectively improving the convenience and efficiency of sampling. It avoids the problems of difficult position adjustment and laborious drilling in traditional sampling, ensuring that the sampling work can be carried out stably and orderly, and better meeting the sampling needs.

[0058] Please refer to Figures 1-5The displacement mechanism 3 includes a vertical rail 31, which is bolted to the side of the upright plate 2 away from the handrail frame 4. A first lead screw 32 is rotatably connected inside the vertical rail 31. A third motor 33 is fixedly installed on the top of the vertical rail 31. The output end of the third motor 33 is fixedly connected to the top of the first lead screw 32 via a coupling. A slider 34 is threadedly connected to the outer surface of the first lead screw 32. The slider 34 is slidably connected inside the vertical rail 31. A mounting base 61 is fixedly installed on the end of the slider 34 away from the upright plate 2. The adjustment module 64 includes a fixed plate 641, which is fixedly installed on the upper part of the inner side of the mounting frame 63. A second motor 642 is fixedly installed on the top of the fixed plate 641, and a second lead screw 643 is fixedly installed on the bottom of the fixed plate 641. The second lead screw 643 is rotatably connected to the bottom of the fixed plate 641. The top of the second lead screw 643 is connected to the output end of the second motor 642 via a coupling. A sliding frame 644 is threaded onto the outer surface of the second lead screw 643. A sliding frame 645 is fixedly installed on the bottom of the fixed plate 641. The sliding frame 644 is slidably connected to the inner side of the sliding frame 645. The bottom of the sliding frame 644 is connected to the top of the transmission module 68. The sampling module 67 includes a receiving hole 671 and an inner rail frame 672. The receiving holes 671 are linearly arranged at equal intervals on both sides of the drilling cylinder 65. The inner rail frames 672 are linearly arranged at equal intervals and fixedly installed on both sides of the inside of the drilling cylinder 65. The inner rail frames 672 are all located inside the receiving holes 671. The inner rail frames 672 slide inside the receiving holes 671. A movable plate 673 is connected to the drill bit 65. A sampling component 674 is fixedly installed on the outer side of the movable plate 673. The sampling component 674 is slidably connected to the inside of the receiving hole 671. The inner side of the movable plate 673 is connected to the transmission module 68. The transmission module 68 includes a side sliding groove 681 and a sliding rod 682. The side sliding groove 681 is arranged in a ring at equal intervals inside the drill bit 65. The sliding rod 682 is slidably connected to the inner side of the side sliding groove 681. A strip-shaped groove 683 is provided on both sides of the sliding rod 682. An inner hinge seat 684 is fixedly installed on the inner side of the strip-shaped groove 683 in a linear arrangement at equal intervals. A linkage frame 685 is hinged to the inner side of the inner hinge seat 684. A side plate 686 is fixedly installed at both ends of the outer side of the linkage frame 685. The inner side of the side plate 686 is connected to the movable plate 673. The sampling assembly 674 is rotatably connected to the middle of both sides of the plate 673. It includes a connecting rod 6741, which is fixedly installed on the middle of the outer side of the movable plate 673. A fixing seat 6742 is fixedly installed at the outer end of the connecting rod 6741. A sampling block 6743 is fixedly installed on the outer side of the fixing seat 6742. A sampling guide cone 6744 is fixedly installed on the outer side of the sampling block 6743. Sampling grooves 6745 are evenly spaced and arranged in a ring on the outer surface of the sampling block 6743. The drilling thread head 66 is also conical in shape. During application, the device, through the coordinated operation of the displacement mechanism 3, adjustment module 64, sampling module 67, transmission module 68, and sampling assembly 674, allows for precise positioning based on the actual location of the target sampling point.The third motor 33 at the top of the vertical rail 31 of the displacement mechanism 3 is activated. The output end of the third motor 33 drives the first lead screw 32, which is rotated inside the vertical rail 31, to rotate synchronously through a coupling. Since the slider 34, which is threaded on the outer surface of the first lead screw 32, is slidably connected inside the vertical rail 31, the rotation of the first lead screw 32 will cause the slider 34 to slide smoothly along the length of the vertical rail 31. The mounting seat 61, which is fixedly installed on the end of the slider 34 away from the vertical plate 2, will move together with the slider 34, thereby accurately adjusting the relevant structures involved in subsequent sampling to the height and horizontal position corresponding to the target sampling point. This lays the foundation for accurate sampling and avoids inaccurate sampling data due to initial position deviation. Subsequently, when drilling and sampling operations are required, the adjustment mechanism is activated. The second motor 642 at the top of the fixed disk 641 in the module 64 drives the second lead screw 643, which is rotatably connected to the bottom of the fixed disk 641, to rotate via a coupling. The sliding frame 644, which is threaded to the outer surface of the second lead screw 643, will slowly slide along the inner side of the sliding frame 645 fixed at the bottom of the fixed disk 641. The transmission module 68 connected to the bottom of the sliding frame 644 will move synchronously with the movement of the sliding frame 644. During the operation of the transmission module 68, the sliding rod 682 will slide along the inner side of the side sliding grooves 681 arranged in an evenly spaced ring inside the drilling barrel 65. The inner hinge seats 684, which are linearly arranged in an evenly spaced manner in the strip grooves 683 on both sides of the sliding rod 682, will gradually expand or contract with the hinged linkage frame 685. The side plates 686 fixed at both ends of the outer side of the 685 drive the movable plate 673 rotatably connected to it in the sampling module 67 to slide along the inner rail frame 672, which is linearly and evenly arranged on both sides of the inside of the drilling cylinder 65. The sampling component 674 fixed on the outer side of the movable plate 673 will extend or retract from the storage holes 671, which are linearly and evenly arranged on both sides of the drilling cylinder 65, as the movable plate 673 slides, realizing flexible extension and retraction control of the sampling component 674. When the sampling component 674 extends outward, the fixing seat 6742 fixed at the outer end of the connecting rod 6741 in the sampling component 674 will bring the sampling block 6743 into the soil simultaneously. The sampling guide cone 6744 fixed on the outer side of the sampling block 6743 can reduce the soil's impact on the sampling block 6743 when it comes into contact with the soil. The resistance helps the sampling block 6743 smoothly insert into soil layers at different depths. Simultaneously, the sampling grooves 6745, evenly spaced in a ring on the outer surface of the sampling block 6743, can stably accommodate soil samples at corresponding depths, ensuring that samples at each depth are completely retained without spillage. The drilling thread head 66 fixed at the bottom of the drilling cylinder 65, due to its conical shape, effectively breaks through the soil structure as the drilling cylinder 65 moves downwards, reducing the overall resistance of the soil to the drilling cylinder 65 during drilling. This allows the drilling cylinder 65 to penetrate more smoothly to the set sampling depth. This multi-mechanism collaborative design not only allows for more precise pre-sampling position adjustments but also ensures smooth and orderly drilling and sampling actions, avoiding the problems of difficult position adjustment, high resistance, and easily damaged samples in traditional sampling methods.This ensured the stability and integrity of soil sample collection at different depths, effectively improving sampling efficiency and better meeting the need for precise soil sample collection.

[0059] Please refer to Figures 1-5 The movable base 1 includes a base 11, an upright plate 2 fixedly installed on the top side of the base 11, and universal wheel frames 12 rotatably connected to the four corners of the bottom of the upright plate 2. Universal wheel bodies 13 are rotatably connected to the bottom of the universal wheel frames 12. A housing 14 is fixedly installed on the top of the base 11. A battery is installed inside the housing 14, and a controller is located in the middle of the top of the housing 14. Support frames 5 are fixedly installed at both ends of the upright plate 2 on the side away from the displacement mechanism 3. The bottom of the support frame 5 is fixedly connected to the top of the base 11. The outer edges of the base 11, support frame 5, and upright plate 2 are all rounded. A connecting frame 15 is fixedly installed on the upper outer side of the support frame 5, and a handrail frame 4 is fixedly installed on the outer end of the connecting frame 15. An anti-slip handrail glove is fixedly installed on the outer side of the handrail frame 4. During the application of this device, the arrangement of the base 11, caster frame 12, caster body 13, chassis 14, controller, upright plate 2, support frame 5, handrail frame 4, and anti-slip handrail glove allows the operator to grip the handrail first. The push device of frame 4 and the anti-slip handgrip on the outside of the handrail frame 4 increase the friction between the hand and the handrail frame 4, preventing slippage during pushing. The universal wheel frame 12 at the four corners of the base 11, together with the universal wheel body 13, allows the device to turn and move flexibly, making it easy to adjust the device to the required position. The housing 14 on the top of the base 11 is equipped with a battery to provide power to the device, eliminating the need for an external power source. The controller on the top of the housing 14 allows the operator to directly operate and control the operation of the device. The upright plate 2 is connected to the base 11 through the support frames 5 on both sides, which enhances the support stability of the upright plate 2 and prevents the device from shaking during operation. The corners of the base 11, support frames 5 and the outer surface of the upright plate 2 are rounded to prevent the operator from being injured by sharp corners. This design makes the device more flexible to move, safer to operate and more stable when used in the field. It also reduces the need for frequent adjustments to the external power source and reduces safety hazards during operation, better adapting to the needs of field sampling.

[0060] The implementation principle of the method for dynamic analysis of sediment sources in a small watershed according to an embodiment of this application is as follows: When staff need to use this device to carry out sampling work for sediment source analysis in a small watershed, they first push the entire device through the handrail 4. The anti-slip handrail gloves on the outside of the handrail 4 can increase the friction between the hand and the handrail 4, preventing slippage during pushing. At the same time, the universal wheel frame 12 and universal wheel body 13 at the bottom of the moving base 1 cooperate to enable the device to move flexibly in the complex terrain of the small watershed in the loess hilly area with broken surface and crisscrossing gullies. The base 11 of the moving base 1 provides stable support for the entire device. The support frame 5 at the top of the base 11 is connected to the upright plate 2, which can enhance the stability of the upright plate 2. The corners of the outer surface of the upright plate 2 are rounded to prevent staff from being bumped and injured during operation. The casing 14 at the top of the base 11 is equipped with a battery, which can provide independent power supply for the device without relying on an external power source, adapting to field sampling scenarios. The controller of the unit is used to centrally control the actions of each mechanism, thereby ensuring that the equipment can be accurately moved to the target sampling points such as the reference point of the study area, slope, sediment profile of the silt dam, or source type area determined in this technical solution. When the equipment reaches the target sampling point, the displacement mechanism 3 is started by the controller. After the vertical rail 31 of the displacement mechanism 3 is fixed, the third motor 33 at the top of it is started. The output end of the third motor 33 drives the first lead screw 32 inside to rotate. Since the slider 34 is threadedly connected to the first lead screw 32 and slidably connected inside the vertical rail 31, the rotation of the first lead screw 32 makes the slider 34 slide up and down along the vertical rail 31. The mounting seat 61 of the sampling mechanism 6 is fixed at the end of the slider 34 away from the vertical plate 2. Therefore, the movement of the slider 34 will synchronously drive the entire sampling mechanism 6 to move up and down, thereby adjusting the drilling cylinder 65 of the sampling mechanism 6 to a suitable initial height from the ground surface of the sampling point, preparing for subsequent drilling and sampling work.

[0061] After adjusting the initial height of the sampling mechanism 6, the first motor 62 at the top of the sampling mechanism 6 is started by the controller. The output end of the first motor 62 drives the main frame 63 to rotate. The bottom of the main frame 63 is fixedly connected to the drilling cylinder 65. Therefore, the rotation of the main frame 63 will drive the drilling cylinder 65 to rotate synchronously. The bottom of the drilling cylinder 65 is fixedly provided with a drilling thread head 66. The drilling thread head 66 is conical in shape. During the rotation of the drilling cylinder 65, it can reduce the resistance of the soil to the drilling cylinder 65, so that the drilling cylinder 65 can drill into the soil smoothly. At this time, the displacement mechanism 3 is controlled by the controller to slowly lower the drilling cylinder 65 to ensure that the drilling cylinder 65 can drill into the set depth according to the sampling requirements of this technical solution.After the drill barrel 65 drills to the set depth range, the controller starts the second motor 642 of the adjustment module 64. The fixing plate 641 of the adjustment module 64 is fixed inside the upper end of the mounting frame 63, providing stable support for the second motor 642 and the second lead screw 643. The output end of the second motor 642 drives the second lead screw 643 to rotate. Since the sliding frame 644 is threadedly connected to the second lead screw 643 and slidably connected to the inner side of the slide 645 at the bottom of the fixing plate 641, the rotation of the second lead screw 643 allows the sliding frame 644 to move vertically downward along the slide 645. The bottom of the sliding frame 644 is connected to the top of the transmission module 68, so the movement of the sliding frame 644 will... The transmission module 68 moves downward synchronously inside the drilling barrel 65. The sliding rod 682 of the transmission module 68 is slidably connected to the inner side of the side sliding groove 681 inside the drilling barrel 65. The side sliding groove 681 provides vertical sliding guidance for the sliding rod 682 to prevent it from deviating during movement. During the downward movement of the sliding rod 682, the inner hinge seats 684 in the strip-shaped grooves 683 on both sides will drive the linkage frame 685 to unfold. The side plates 686 at both ends of the outer side of the linkage frame 685 are rotatably connected to the middle of the two sides of the movable plate 673 of the sampling module 67. The unfolding of the linkage frame 685 pushes the movable plate 673 to slide along the inner rail frame 672. The inner rail frame 672 is fixed inside the drilling barrel 65 on both sides. Located inside the receiving hole 671, it provides a sliding track for the movable plate 673. A sampling component 674 is fixedly installed on the outer side of the movable plate 673. The sampling component 674 moves synchronously with the movable plate 673, allowing it to extend from the receiving hole 671 on the side wall of the drilling cylinder 65 into the soil outside the drilling cylinder 65. A fixing seat 6742 is provided at the outer end of the connecting rod 6741 of the sampling component 674. A sampling block 6743 is provided on the outer side of the fixing seat 6742. A sampling guide cone 6744 is provided on the outer side of the sampling block 6743 to reduce the resistance of the sampling component 674 extending into the soil. A sampling groove 6745 is opened on the outer surface of the sampling block 6743. When the sampling groove 6743 is opened, a sampling guide cone 6744 is provided on the outer side of the sampling block 6743 to reduce the resistance of the sampling component 674 extending into the soil. When the sampling guide cone 6744 is inserted into the soil, the soil pressure can enter the interior of the sampling groove 6745. After sampling is completed, the second motor 642 can be started to run in reverse, which can drive the linkage frame 685 to pull the sampling block 6743 back. The sampling block 6743 retracts into the storage hole 671. At this time, the sampling groove 6745 retracts to further scrape the soil sample, so that the sample can enter the inner side of the sampling groove 6745 better. After sampling is completed, the sampling block 6743 enters the storage hole 671. The storage hole 671 can cover the sampling groove 6745, thereby better preserving the sampled soil and avoiding soil contamination.

[0062] After sampling is completed, the controller controls the second motor 642 of the adjustment module 64 to reverse, which drives the second lead screw 643 to rotate in the opposite direction, causing the sliding frame 644 to move vertically upward along the sliding frame 645. The sliding frame 644 pulls the sliding rod 682 of the transmission module 68 to move upward along the side slide groove 681. The upward movement of the sliding rod 682 causes the linkage frame 685 to retract. The linkage frame 685 pulls the movable plate 673 along the inner rail frame 672 into the drilling cylinder 65 via the side plate 686. The movable plate 673 drives the sampling component 674 to retract synchronously into the receiving hole 671, preventing soil samples from spilling during the lifting process of the sampling component 674. The controller starts the third motor 33 of the displacement mechanism 3 to reverse, and the third motor 33 drives the first lead screw 32 to rotate in the opposite direction, so that the slider 34 drives the sampling mechanism 6 to rise as a whole, and the drilling cylinder 65 is separated from the soil. After the drilling cylinder 65 moves up and is separated from the soil, the second motor 642 is started again to drive the sampling block 6743 to move outward and extend out of the storage hole 671 to expose the sampling slot 6745, so that the sample can be quickly taken out. It can be seen that the design of the multiple sampling modules 67 synchronously extending and retracting in this device can sample soil at different depths during a single drilling, and the whole device can accommodate soil at the corresponding depth, thereby realizing the synchronous collection of soil at different depths in the drilling cylinder 65.

[0063] Workers open sampling component 674 and extract soil samples from different depths from sampling slot 6745 of sampling block 6743. Following the requirements of this technical solution, these samples are placed in dedicated sample bags and labeled with relevant information. The extracted soil samples are then processed according to the following procedures: air-drying in a ventilated drying room, grinding with a grinder, removing impurities through a soil sieve, weighing, placing in a dedicated sealed sample box, and sending to the laboratory for measurement and recording of nuclide activity values ​​using a low-background gamma spectrometer. Further work will then be conducted, including determining the nuclide input background value, defining the time of sediment deposition in silt-retaining dams, measuring fingerprint identification factors, and calculating the source contribution rate. This technical solution, through the coordinated use of the above structures, solves many problems of existing sampling equipment. First, this device enables simultaneous collection of soil samples from different depths without multiple drilling operations, improving sampling efficiency. It also ensures that samples from different depths come from the same sampling point, reducing spatial deviation and solving the problem that existing equipment can only obtain soil samples from the deepest location. Second, the precise control of each mechanism ensures… This method ensures accurate sampling depth, avoids poor sample representativeness, and solves the analytical errors caused by inaccurate depth control in traditional sampling methods. Furthermore, the flexible mobility and independent power supply design of the equipment adapt to the complex field environment of small watersheds, solving the problems of inconvenient movement and reliance on external power supply of traditional equipment. In addition, the samples obtained by simultaneous sampling can meet the complementary needs of different nuclides in radioisotope tracing research, providing high-quality samples for subsequent nuclide measurement and data analysis, thereby improving the accuracy of erosion rate calculation and sediment source analysis in small watersheds, and providing a scientific basis for the optimal configuration of soil and water conservation measures.

[0064] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for dynamic analysis of sediment sources in a small watershed, characterized in that, Includes the following steps: Step 1: Selection of research subjects. In the Loess Hilly Area, small watersheds are selected as research areas. These areas should include long-term series of rainfall, runoff, and sediment observation data. The slopes and small watersheds of cultivated land, forest land, grassland, and reclaimed farmland are identified as research subjects. Step 2: Conduct field investigations to collect data on topography, precipitation, runoff, sediment, land use, and soil and water conservation records for the study area; investigate the parameters of the Menhulu Dam, land use distribution and historical changes, and vegetation restoration after farmland conversion; use drones to acquire images and combine them with remote sensing to interpret land use changes in the small watershed. Step 3: Soil sampling at reference points. Select non-eroded flat land or old terraces as reference points. After setting up the points, use sampling equipment to collect full profile and layered soil samples, and label the sampling information. Step 4: Reference point sample processing. After the soil sample is naturally air-dried, it is ground, sieved to remove impurities, sealed and placed before being sent for testing of 137Cs and 210Pbex activities, and the data is recorded. Step 5: Determine the background nuclide and sedimentation flux. Organize the nuclide data of the reference point, combine it with geographical and precipitation data to calculate the infiltration coefficient, and determine the background nuclide value and 210Pbex sedimentation flux; Step Six: Slope soil sampling. The land is divided into disturbed and undisturbed land. Disturbed land mainly consists of slopes that have been converted from farmland, while undisturbed land includes woodland, grassland, and wasteland. Sampling points are selected on the slope, and sampling equipment is used to take samples at different depths based on soil thickness. Sampling information is then marked. Step 7: Slope sample preparation. Prepare slope soil samples according to Step 4, send them for nuclide activity testing, and record the data. Step 8: Sampling of sediment at the silt-retaining dam. Select the sampling point at the silt-retaining dam, excavate the sediment profile, identify the sedimentary cycles, and then sample in layers, measure the thickness and label the information. Step Nine: Determine the time of sedimentation layers, adjust precipitation data to find the time of major floods, check dam records to confirm key nodes; measure the 137Cs activity of sedimentation layers to determine the time of sedimentation layers such as the year of dam construction and before and after land reclamation; Step 10: Source analysis. The dam-controlled area is designated as the source area. Samples are taken to measure fingerprint factors such as soil particle composition, soil nutrients, and radionuclide activity values. The contribution rate is calculated and compared before and after the land conversion, and the changes in sediment sources are analyzed.

2. The method for dynamic analysis of sediment sources in a small watershed according to claim 1, characterized in that: The sampling device includes a movable base (1), a vertical plate (2) is fixedly installed on the top of the movable base (1), a displacement mechanism (3) is fixedly installed on the front of the vertical plate (2), and a sampling mechanism (6) is fixedly installed on the moving end of the displacement mechanism (3). The sampling mechanism (6) includes a mounting base (61), which is fixedly mounted on the moving end of the displacement mechanism (3). A first motor (62) is fixedly mounted on the top of the mounting base (61), and a mounting main frame (63) is fixedly mounted on the output end of the first motor (62). An adjustment module (64) is fixedly mounted on the inner side of the mounting main frame (63). A drilling cylinder (65) is fixedly mounted on the bottom of the mounting main frame (63), and a drilling thread head (66) is fixedly mounted on the bottom of the drilling cylinder (65). Sampling modules (67) are movably mounted on both sides of the inside of the drilling cylinder (65) in a linear arrangement with equal spacing. A transmission module (68) is movably mounted inside the drilling cylinder (65). The top of the transmission module (68) is connected to the bottom of the adjustment module (64), and the transmission module (68) and the sampling module (67) are connected by transmission.

3. The method for dynamic analysis of sediment sources in a small watershed according to claim 2, characterized in that: The movable base (1) includes a base (11), the upright plate (2) is fixedly installed on the top side of the base (11), and the bottom four corners of the upright plate (2) are rotatably connected to universal wheel frames (12). The bottom of the universal wheel frames (12) is rotatably connected to universal wheel bodies (13). The top of the base (11) is fixedly installed with a chassis (14). The inside of the chassis (14) is equipped with a storage battery, and the top center of the chassis (14) is equipped with a controller.

4. The method for dynamic analysis of sediment sources in a small watershed according to claim 3, characterized in that: The upright plate (2) is fixedly installed with a support frame (5) on both ends of the side away from the displacement mechanism (3). The bottom of the support frame (5) is fixedly connected to the top of the base (11). The outer surface corners of the base (11), the support frame (5) and the upright plate (2) are all set as arcs.

5. The method for dynamic analysis of sediment sources in a small watershed according to claim 4, characterized in that: A connecting frame (15) is fixedly installed on the upper outer side of the support frame (5), and a handrail frame (4) is fixedly installed on the outer side of the connecting frame (15). An anti-slip handrail glove is fixedly installed on the outer side of the handrail frame (4).

6. The method for dynamic analysis of sediment sources in a small watershed according to claim 5, characterized in that: The displacement mechanism (3) includes a vertical rail (31), which is bolted to the side of the vertical plate (2) away from the handrail (4). A first lead screw (32) is rotatably connected inside the vertical rail (31). A third motor (33) is fixedly installed on the top of the vertical rail (31). The output end of the third motor (33) is fixedly connected to the top of the first lead screw (32) through a coupling. A slider (34) is threadedly connected to the outer surface of the first lead screw (32). The slider (34) is slidably connected inside the vertical rail (31). The mounting seat (61) is fixedly installed on the end of the slider (34) away from the vertical plate (2).

7. The method for dynamic analysis of sediment sources in a small watershed according to claim 6, characterized in that: The adjustment module (64) includes a fixed plate (641), which is fixedly installed on the upper part of the mounting frame (63). A second motor (642) is fixedly installed on the top of the fixed plate (641), and a second lead screw (643) is fixedly installed on the bottom of the fixed plate (641). The second lead screw (643) is rotatably connected to the bottom of the fixed plate (641). The top of the second lead screw (643) is connected to the output end of the second motor (642) through a coupling. A sliding frame (644) is threadedly connected to the outer surface of the second lead screw (643). A sliding frame (645) is fixedly installed on the bottom of the fixed plate (641). The sliding frame (644) is slidably connected to the inner side of the sliding frame (645). The bottom of the sliding frame (644) is connected to the top of the transmission module (68).

8. The method for dynamic analysis of sediment sources in a small watershed according to claim 7, characterized in that: The sampling module (67) includes a receiving hole (671) and an inner rail frame (672). The receiving holes (671) are linearly arranged at equal intervals on both sides of the drilling cylinder (65). The inner rail frames (672) are linearly arranged at equal intervals and fixedly installed on both sides of the inside of the drilling cylinder (65). The inner rail frames (672) are all located inside the receiving holes (671). A movable plate (673) is slidably connected inside the inner rail frame (672). A sampling component (674) is fixedly installed on the outside of the movable plate (673). The sampling component (674) is slidably connected inside the receiving hole (671). The inside of the movable plate (673) is connected to the transmission module (68).

9. The method for dynamic analysis of sediment sources in a small watershed according to claim 8, characterized in that: The transmission module (68) includes a side slide groove (681) and a sliding rod (682). The side slide groove (681) is arranged in a ring at equal intervals inside the drill barrel (65). The sliding rod (682) is slidably connected to the inner side of the side slide groove (681). A strip groove (683) is provided on both sides of the sliding rod (682). An inner hinge seat (684) is fixedly installed on the inner side of the strip groove (683) in a linear arrangement at equal intervals. A linkage frame (685) is hinged to the inner side of the inner hinge seat (684). A side plate (686) is fixedly installed at both ends of the outer side of the linkage frame (685). The inner side of the side plate (686) is rotatably connected to the middle of both sides of the movable plate (673).

10. The method for dynamic analysis of sediment sources in a small watershed according to claim 9, characterized in that: The sampling assembly (674) includes a connecting rod (6741), which is fixedly installed on the outer middle of the movable plate (673). A fixing seat (6742) is fixedly installed on the outer end of the connecting rod (6741). A sampling block (6743) is fixedly installed on the outer side of the fixing seat (6742). A sampling guide cone (6744) is fixedly installed on the outer side of the sampling block (6743). Sampling grooves (6745) are evenly spaced and arranged in a ring on the outer surface of the sampling block (6743). The drilling thread head (66) is also cone-shaped.

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