A five-zone three-stage double-cycle surface source pollution prevention and control system

Abstract

The present application relates to the technical field of agricultural non-point source pollution prevention and control and slope farmland soil and water conservation, and particularly relates to a five-zone three-stage double-cycle slope farmland non-point source pollution prevention and control system, which comprises, from top to bottom along the slope, an abrupt slope source head control zone, a middle slope soil flow nutrient interception zone, a regulation and storage moisture stabilization zone, a gentle slope ecological interception double purification ditch zone and an ecological pool recycling zone, forming a five-zone prevention and control system; wherein the abrupt slope source head control zone constitutes a source head control barrier, the middle slope soil flow nutrient interception zone and the gentle slope ecological interception double purification ditch zone constitute a process interception and purification barrier, and the regulation and storage moisture stabilization zone and the ecological pool recycling zone constitute a terminal stabilization maintenance and recycling barrier. In the system operation, the purified tail water is recycled for irrigation, water replenishment or soil moisture conservation to form a water cycle, and agricultural waste is used as an adsorption, carbon source or moisture retention material and is renewed to form a material cycle. The present application can realize hierarchical interception of runoff and soil flow, nitrogen and phosphorus reduction, denitrification and purification, and resource recycling.

Description

Technical Field

[0001] This invention relates to the fields of agricultural non-point source pollution control, soil and water conservation in sloping farmland, and ecological purification of farmland runoff. Specifically, it relates to a five-zone, three-level, dual-circulation non-point source pollution control system, which is applicable to sloping farmland in rocky mountainous areas. The system is an engineering system that uses slope zoning for source control, diversion and adsorption purification of inter-soil flow, regulation and moisture retention, dual purification and denitrification in ditches, and wastewater reuse. Background Technology

[0002] Sloping farmland is an important area for agricultural production in hilly regions. However, due to its large slope undulations, concentrated rainfall, close connection between gullies and slopes, and frequent disturbance from cultivation, it is prone to surface runoff, shallow interflow, and sediment migration after rainfall, resulting in the loss of nutrients such as nitrogen and phosphorus, which in turn leads to agricultural non-point source pollution. Especially in the Danjiangkou Reservoir area and similar small watersheds in rocky mountainous areas, sloping farmland is characterized by rapid runoff generation on the upper steep slope, active lateral seepage in the middle, and concentrated runoff at the lower slope, with significant differences in slope position in the processes of soil erosion and nutrient migration.

[0003] Current technologies for controlling surface source pollution on sloping farmland often employ single measures such as terracing, earthen embankments, vegetation hedges, sedimentation ponds, or ecological ponds. Some solutions also include setting up ecological interception ditches or plant purification units at the toe of the slope or in low-lying channels to treat runoff. While these measures can reduce surface flow velocity, intercept sediment, or absorb some nitrogen and phosphorus to some extent, they still have the following shortcomings: First, existing measures are usually not zoned according to the different soil and water loss mechanisms of different slope sections. Steep slopes are mainly characterized by strong runoff erosion and scouring at the toe; medium slopes are mainly characterized by a combination of shallow runoff and interflow; and gentle slopes and toe sections are mainly characterized by upstream runoff and channel transport. If similar measures are used uniformly, it often results in insufficient erosion reduction on steep slopes, uncontrolled interflow on medium slopes, and excessive purification load on gentle slope channels. Second, while traditional slope-to-terrace conversion can shorten slope length, steep slopes are prone to concentrated overflows at the outer edges after repeated erosion by heavy rainfall, leading to erosion at the toe, local instability, and even collapse. This fails to fundamentally solve the long-term erosion stability problem of steep slopes. Third, ordinary earthen embankments, stone embankments, or general ditch interception structures mainly target surface runoff and have limited control over dissolved nitrogen and phosphorus in shallow interflows on mid-slopes. Especially when interflows migrate laterally along the lower part of the topsoil, they easily bypass surface interception measures and continue to flow downstream. Fourth, existing ditch-type purification measures mostly focus on diversion or plant absorption, lacking a composite structure that simultaneously considers deceleration and sedimentation, plant absorption, microbial attachment, and denitrification. They also lack moisture-retaining and regulating structures to maintain a stable microbial living environment under intermittent flow conditions, resulting in a decrease in the system's denitrification capacity during prolonged droughts or intermittent water flow. Fifth, purified effluent is often directly discharged, with insufficient connection to farmland reuse and agricultural waste resource utilization, making it difficult to form a closed-loop treatment system that combines water and material cycles.

[0004] The above analysis shows that existing technologies cannot adapt to the characteristics of soil and water loss in different slope sections of sloping farmland, and they do not take into account the systematic combination of steep slope stabilization and erosion reduction, mid-slope soil flow control, gully dual purification and denitrification, habitat maintenance during the dry season, and tailwater reuse. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a five-belt, three-level, dual-circulation non-point source pollution control system. This system overcomes the shortcomings of existing technologies, such as insufficient adaptability to soil erosion characteristics on different slope sections of sloping farmland, inadequate control of interflow, susceptibility of steep slopes to repeated erosion and instability of traditional terraced fields, lack of a stable microbial environment for denitrification in ditches, and insufficient connection for tailwater reuse. By setting up different engineering units on different slope sections, it achieves continuous control, adsorption and purification, microbial denitrification, and tailwater reuse of slope runoff, interflow, sediment, nitrogen, and phosphorus.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A five-belt, three-level, dual-circulation system for the prevention and control of surface pollution in sloping farmland includes, from top to bottom, a steep slope source control zone, a medium slope soil nutrient interception zone, a water storage and moisture retention zone, a gentle slope ecological interception and purification ditch zone, and an ecological pond reuse zone. The steep slope source control zone is deployed on slope sections with an angle of 16° to 25°, and it features reverse slope steps along contour lines. This zone is located on steep slope sections where surface runoff energy is highest, erosion is strongest, and the embankment is most prone to instability. Unlike traditional slope-to-terrace conversions or stone / earth embankments, which easily lead to concentrated overflow at the outer edge and erosion at the embankment toe, this invention uses reverse slope steps to preferentially disperse and retain incoming water towards the inner side of the steps, reducing outflow erosion at the outer edge and erosion at the embankment toe, and lowering the risk of collapse after continuous erosion on steep slope sections.

[0007] The medium-slope soil nutrient interception zone is laid out on slopes with a slope of 6° to 15°. It is provided with embedded adsorption ridges at intervals along the contour lines. The embedded adsorption ridges are provided with through core grooves along the length of the ridges. The core grooves are provided with adsorption material layers so that the shallow soil in the zone can enter the through core grooves and pass through the adsorption material layers under the action of the flow-guiding and seepage-blocking layer. The regulating and moisturizing steady-state zone is equipped with a regulating and moisturizing tank. The regulating and moisturizing tank is lined with a capillary water replenishment layer and a water storage matrix layer from bottom to top, which is used to slowly release water to the downstream plant-microbe denitrification and purification zone during periods of no continuous water supply or interruption of flow. Specifically, the capillary water replenishment layer is located between the water storage matrix layer and the downstream plant-microbe denitrification and purification zone, and is in contact with and connected to the water storage matrix layer. The regulating and moisturizing steady-state zone is used to slowly release water to the downstream plant-microbe denitrification and purification zone during periods of no continuous water inflow or interruption of flow, in order to maintain a moist environment in the plant rhizosphere and microbial attachment layer; the plant-microbe denitrification and purification zone forms an alternating aerobic-anoxic-anaerobic microenvironment through the plant rhizosphere, filler pores and carbon source matrix, so that denitrifying microorganisms can convert nitrate nitrogen into nitrogen gas; the capillary water replenishment layer is preferably made of agricultural waste through crushing, pressing, weaving or composite processing to form a fiber layer, fiber felt or porous water-conducting layer, the agricultural waste including one or more of straw, corn cob, rice husk, coconut coir, sugarcane bagasse and hemp stalk.

[0008] The gentle slope ecological interception dual purification ditch zone is laid in the slope section area or the slope toe confluence area with a slope of no more than 6°, including the ecological interception ditch connected to the downstream of the regulation and moisture retention steady state zone. The ecological interception ditch is arranged in sequence along the water flow direction as a permeable deceleration purification zone and a plant-microorganism denitrification purification zone. The ecological pond reuse zone includes a sedimentation buffer zone, a plant purification zone, and a clear water storage zone connected in sequence. The clear water storage zone is connected to the reuse water intake device. The ecological pond reuse zone is preferably formed by transforming existing low-lying pits, abandoned ponds, or farmland edges.

[0009] The five zones in this invention are, in order: a steep slope source control zone, a mid-slope soil nutrient interception zone, a regulation and moisture retention stabilization zone, a gentle slope ecological interception dual-purification ditch zone, and an ecological pond reuse zone. The steep slope source control zone constitutes the source control unit, primarily responsible for source flow reduction, slope stabilization, and erosion reduction. The mid-slope soil nutrient interception zone and the gentle slope ecological interception dual-purification ditch zone constitute the process interception and purification unit, primarily responsible for process interception, adsorption purification, and ditch denitrification. The regulation and moisture retention stabilization zone and the ecological pond reuse zone constitute the system stability maintenance and end-of-pipe reuse unit, primarily responsible for maintaining a humid environment, deep purification, and tailwater reuse. The system in this invention can form an operation mode that combines water circulation and material circulation: the first is water circulation, that is, the tailwater after purification in each zone enters the ecological pond reuse zone and is used for farmland irrigation, economic forest water replenishment or dry season moisture retention; the second is material circulation, that is, agricultural waste such as straw, corn cobs, pruning residues and other agricultural waste enters the system as biochar, carbon source matrix or moisture-retaining matrix, and after renewal, it returns to the farmland in the form of compost or resource utilization.

[0010] In another preferred embodiment, the width of the reverse slope step is 1.5m to 2.5m, the step surface forms a reverse slope angle of 5° to 10° on the inner side of the slope, and a low embankment or vegetation stabilization strip is provided at the outer edge of the reverse slope step.

[0011] In another preferred embodiment, the height of the embedded adsorption ridge is 0.40m to 0.80m, and the top width is 0.30m to 0.60m; The embedded adsorption embankment is provided with a through core groove along the length of the embankment. The width of the core groove is 0.25m to 0.35m and the depth is 0.35m to 0.45m. The water-facing side of the core groove is provided with a flow-guiding and seepage-blocking layer made of compacted clay with a thickness of 0.10m to 0.20m. The medium-slope soil nutrient interception zone is equipped with no less than two embedded adsorption ridges, with a slope spacing of 15m to 25m between adjacent embedded adsorption ridges; when the slope is 6° to 10°, the slope spacing is 20m to 25m; when the slope is 10° to 15°, the slope spacing is 15m to 20m.

[0012] In another preferred embodiment, the adsorbent material layer is composed of a gravel guiding layer, a zeolite adsorption layer, a biochar adsorption layer, and a soil cover layer from bottom to top. The shallow soil in the mid-slope soil nutrient interception zone can be collected along the water-facing side under the blocking effect of the guiding and seepage-blocking layer and forced into the through-type core trench, passing through the gravel guiding layer, zeolite adsorption layer and biochar adsorption layer in sequence, thereby achieving the interception and adsorption of dissolved nitrogen and phosphorus. The gravel diversion layer has a thickness of 0.08m to 0.15m, the zeolite adsorption layer has a thickness of 0.08m to 0.15m, the biochar adsorption layer has a thickness of 0.08m to 0.12m, and the soil cover layer has a thickness of 0.05m to 0.10m.

[0013] In another preferred embodiment, the water-retaining substrate layer is composed of one or more of the following: crushed stone, gravel, biochar, coconut coir, and straw fiber blanket.

[0014] In another preferred embodiment, subsurface flow dams are set at intervals of 4m to 8m along the water flow direction of the ecological interception ditch within the permeable deceleration and purification zone; the subsurface flow dams are filled with a filter material layer with permeable and adsorption functions, the filter material layer being composed of a fine sand layer and a sandy planting soil layer located above the fine sand layer, in order to slow down the water flow speed in the ditch and enhance the nitrogen and phosphorus removal effect.

[0015] The filter media layer is filled with crushed agricultural waste carbon source in the upper part of the fine sand layer or at the junction of the fine sand layer and the sandy planting soil layer; the agricultural waste carbon source is one or more of straw, corn cob, and rice husk, in order to further enhance the denitrification process.

[0016] In another preferred embodiment, emergent and submerged plants are arranged within the plant-microbial denitrification and purification zone, which is filled with a carbon source matrix. The carbon source matrix includes any one or more components selected from corn cobs, straw segments, sawdust, and biochar particles. The plant rhizosphere, the pores of the filler, and the carbon source matrix together form an alternating aerobic-anoxic-anaerobic microenvironment, providing a stable habitat for attached microorganisms. The carbon source matrix provides a continuous carbon source for denitrifying microorganisms, enabling nitrate nitrogen in the water to be converted into nitrogen gas and discharged under anoxic conditions through denitrification, thereby reducing the nitrogen pollution load.

[0017] In another preferred embodiment, the ecological interception ditch is continuously laid out along the gentle slope area, the toe of the slope confluence area, and the downstream connecting section, forming a hydraulic connection with the upstream outflow ends and the downstream inflow ends of each zone. The ecological interception ditch adopts a trapezoidal cross-section, with a bottom width of 0.6m to 1.0m, a depth of 0.5m to 0.8m, and a side slope ratio of 1:1 to 1.5. A permeable stabilizing layer is laid at the bottom of the ditch. Along the water flow direction, a permeable deceleration and purification zone and a plant-microorganism denitrification and purification zone are sequentially set within the ecological interception ditch.

[0018] In another preferred embodiment, the ecological pond reuse zone is formed by transforming low-lying pits, abandoned ponds, or farmland edges.

[0019] In another preferred embodiment, at least one of the regulating and moisturizing steady-state zone, the ecological interception ditch, and the ecological pond reuse zone is provided with a safety overflow outlet and a drainage channel.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention sets up different functional zones according to slope gradient, and conducts zoned treatment to address the different characteristics of soil and water loss, such as strong erosion on steep slopes, active interflow on medium slopes, and concentrated gully transport on gentle slopes. This improves the matching between engineering measures and slope erosion mechanisms.

[0021] By setting up reverse slope steps on steep slope sections, water from the slope surface is dispersed and retained on the inner side of the steps, reducing the risk of overflow at the outer edge and scouring at the foot of the slope. Compared with traditional slope-to-terrace conversion, this method is more conducive to improving the erosion resistance and long-term operational stability of steep slope sections.

[0022] By setting up embedded adsorption ridges on the middle slope, and controlling the flow path of the soil interflow together with the flow-guiding and seepage-blocking layer and the through core groove, the shallow soil interflow is guided into the adsorption material layer, thereby enhancing the interception capacity of dissolved nitrogen and phosphorus.

[0023] By setting up intermittent subsurface dams, fine sand layer-sand planting soil layer filter media structure and agricultural waste carbon source in the ecological interception ditch, hydraulic deceleration, particulate matter sedimentation and denitrification enhancement can be achieved simultaneously.

[0024] By setting up a plant-microbe denitrification and purification zone and a water-regulating and moisture-retaining steady-state zone, a relatively stable microbial habitat can be maintained during both water-bearing and dry periods, reducing microbial mortality and maintaining the denitrification function.

[0025] By setting up an ecological pond reuse zone, the purified wastewater can be further purified and reused, which helps to form a water recycling method for wastewater reuse. At the same time, agricultural waste can be used as a carbon source or substrate to enter the system and return to the farmland after renewal, realizing the resource utilization of agricultural waste. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention, which is deployed in sections along the slope.

[0027] Figure 2 This is a schematic cross-sectional view of the reverse slope step of the present invention.

[0028] Figure 3 This is a schematic cross-sectional view of the embedded adsorption ridge of the present invention.

[0029] Figure 4 This is a schematic diagram of the structure of the moisture-regulating and hydrating steady-state zone of the present invention.

[0030] Figure 5 This is a schematic diagram of the connection structure between the gentle slope ecological interception double purification ditch and the ecological pond reuse zone of the present invention.

[0031] Figure 6 This is a picture of bare ground at a 25° angle.

[0032] Figure 7 Images of a corn experimental plot.

[0033] Figure 8 These are pictures of the soil extraction process.

[0034] Figure 9 Images of the experimental filtration process. Detailed Implementation

[0035] The technical solutions of this invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] The present invention will be further illustrated below with reference to the field experimental platform, experimental plan, and monitoring data from the Soil and Water Conservation Monitoring Station in Yunxi County, Shiyan City, Hubei Province. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0037] This invention was developed using the soil and water conservation monitoring station in Yunxi County, Shiyan City, Hubei Province. This monitoring station is equipped with runoff plots under natural rainfall conditions, enabling continuous monitoring of slope runoff, sediment production, and nitrogen and phosphorus loss processes under different slope gradients and farmland use types. Based on existing experimental schemes and monitoring data on suspended solids, phosphorus, ammonium nitrogen, and nitrate nitrogen, the slope zoning, functional zone layout, and engineering control logic of this invention are explained. The five-zone, three-level, dual-circulation sloping farmland surface source pollution control system in this invention is as follows: Figure 1 As shown.

[0038] Experimental setup The field experiment at the monitoring station set up 15 typical treatment plots, covering typical slope utilization types such as sloping farmland, slope-to-terrace conversion, bare land, and economic forests.

[0039] Specifically, the experimental results included: sloping farmland plots with maize at slopes of 5°, 15°, and 25°; terraced plots with slopes of 5°, 15°, and 25°, with maize as the crop; bare land control plots with slopes of 5°, 15°, and 25°; and sloping farmland plots with economic forests at slopes of 8°, 15°, and 25°, with walnut trees as the crop. Maize sowing and walnut tree transplanting were conducted with consistent row and plant spacing to eliminate uncontrolled influences of vegetation cover differences on the experimental results. Walnut trees represented high-value economic forests and were planted on the terraced slopes; maize represented a food crop and was planted on other sloping farmland slopes. The planting methods for maize and walnut trees are existing technologies and will not be described in detail here.

[0040] The experimental schemes included fertilization backgrounds of 30% organic fertilizer + 70% chemical fertilizer and 100% chemical fertilizer. These fertilization regimes were used to create different nutrient output backgrounds and obtain monitoring data, but are not considered essential technical features of the engineering system of this invention.

[0041] The stone terrace treatment in the test scheme is used as a reference for existing measures in this embodiment to compare the stability differences of different engineering measures on steep slopes under rainfall erosion conditions, and does not constitute a technical component of the present invention.

[0042] Monitoring indicators and data sources Under natural rainfall conditions, runoff collection and sampling devices were installed at the outlets of each runoff plot to collect slope outflows under different rainfall events, and to measure runoff volume, sediment load, suspended solids concentration, soluble phosphorus, adsorbed phosphorus, ammonium nitrogen, and nitrate nitrogen. The monitoring period covered the period of concentrated rainfall from July to September. Monitoring results showed that there were significant differences in the concentrations of suspended solids, phosphorus, ammonium nitrogen, and nitrate nitrogen among different slopes and different sloping farmland use types, and these concentrations exhibited strong fluctuations across multiple rainfall events, indicating that the output of surface-source pollution from sloping farmland has significant differences in slope, land use type, and process. Therefore, this invention adopts slope zoning and configures differentiated engineering units, supported by an experimental platform and monitoring data.

[0043] Slope zoning based on experimental design and data Based on the typical slope treatments of 5°, 8°, 15°, and 25° set in the monitoring station's experimental plan, and the corresponding suspended solids and nitrogen and phosphorus monitoring data, the control of ground source pollution on sloping farmland can be divided into the following three functional slope sections: The steep slope section (steep slope source control zone) ranges from 16° to 25°, corresponding to the 25° treatment in the experimental scheme, and is considered a slope section with a high risk of surface runoff erosion. Existing monitoring data shows that high suspended solids concentrations were observed in 25° bare land, 25° slopes, and 25° slope-to-terrace treatments during multiple rainfall events. Specifically, the suspended solids concentration in the 25° bare land treatment reached 1.55 × 10⁻⁶ during two rainfall events on July 22nd and August 9th. 4 mg / L~2.85×10 5 mg / L and 1.50×10 4 mg / L~3.68×10 6 mg / L; the suspended solids concentration on the 25° slope reached 1.02 × 10 mg / L during the rainfall on July 22. 4 mg / L~1.76×10 4 mg / L; the suspended solids concentration in the 25° slope-to-terrace treatment area reached 4.60 × 10 mg / L during the rainfall events on July 22 and August 22. 3 mg / L~6.18×10 4 The concentration of mg / L indicates that this slope section is more prone to strong erosion and a higher risk of sediment output. Therefore, this invention designates the steep slope section as a key area for source control and employs reverse slope steps for control.

[0044] The mid-slope section (the mid-slope soil nutrient interception zone) ranges from 6° to 15°, corresponding to the 8° and 15° treatments in the experimental design. Monitoring data showed that nitrogen and phosphorus output occurred in this section during multiple rainfall events, indicating that in addition to surface runoff, nutrient migration control needs to be considered. Specifically, in the 8° treatment samples, ammonium nitrogen concentrations ranged from 0.72 mg / L to 1.62 mg / L, nitrate nitrogen concentrations ranged from 8.14 mg / L to 17.19 mg / L, and phosphorus concentrations ranged from 0.13 mg / L to 3.14 mg / L; in the 15° treatment samples, ammonium nitrogen concentrations ranged from 0.02 mg / L to 1.34 mg / L, nitrate nitrogen concentrations reached as high as 22.33 mg / L, and phosphorus concentrations reached as high as 3.67 mg / L. Based on the hydrological mechanism of slope, the middle slope section is a key section where shallow surface runoff and shallow interflow coexist. Therefore, this invention sets up embedded adsorption embankments in this slope section to control the path of interflow and intercept dissolved nutrients.

[0045] The gentle slope and the runoff section at the foot of the slope (gentle slope ecological interception double purification ditch zone) are no more than 6°. This slope section corresponds to the 5° treatment and gentle slope runoff area in the test scheme. It mainly undertakes the functions of upstream water collection, ditch transport and downstream connection. It is suitable for setting up water storage and moisture retention facilities, ecological interception ditches, permeable deceleration and purification structures, plant-microorganism denitrification structures and subsequent ecological pond reuse facilities.

[0046] The above-mentioned slope zoning is an engineering zoning scheme determined by combining typical slope treatment and monitoring data in the test plan, which can provide a basis for the layout of engineering units of different slope sections in this invention.

[0047] Based on the above analysis results, a specific experiment was conducted, and the specific process is as follows.

[0048] A continuous slope with a steep upper section, a transitional middle section, and a gentle lower section was selected as the implementation target at the Soil and Water Conservation Monitoring Station in Yunxi County, Shiyan City, Hubei Province. A five-zone graded interception and denitrification reuse system was constructed according to the technical solution of this invention. Related experimental images are shown below. Figures 6-9 As shown, the specific settings are as follows: 1. Steep slope source control zone Upward slope steps are laid out along contour lines on the upper steep slope section, such as... Figure 2 As shown, the preferred width of the reverse slope step is 2.0 mm, with the step surface forming an 8° reverse slope angle on the inner side of the slope. A low embankment or vegetation stabilization strip is set at the outer edge. In this embodiment, specifically, a soil embankment with a height of 30 cm is built at the outer edge. The reverse slope step is used to preferentially disperse and retain water from the slope surface towards the inner side of the step surface, reducing the outflow erosion at the outer edge from the source, and reducing the risk of erosion at the toe of the slope and instability of steep slope sections.

[0049] 2. Nutrient interception zone in mid-slope soil Two embedded adsorption embankments are set at 20m intervals along the contour lines on the middle slope section. Figure 3 As shown, each embedded adsorption embankment is equipped with a through-type core trench, which is 0.30m wide and 0.40m deep. A flow-guiding and seepage-blocking layer is provided on the water-facing side of the core trench, which is a compacted clay with a thickness of 0.10m. From bottom to top, the core trench is equipped with a gravel flow-guiding layer, a zeolite adsorption layer, a biochar adsorption layer, and a soil cover protection layer. The gravel flow-guiding layer has a thickness of 0.10m, the zeolite adsorption layer has a thickness of 0.10m, the biochar adsorption layer has a thickness of 0.10m, and the soil cover protection layer has a thickness of 0.10m.

[0050] When the interflow in the shallow soil of the middle slope migrates laterally along the lower part of the cultivated layer, the flow-guiding and seepage-blocking layer can block and guide it, causing it to collect along the water-facing side of the adsorption ridge and enter the through core channel. Then, it passes through the gravel flow-guiding layer, zeolite adsorption layer and biochar adsorption layer in sequence, thereby achieving the interception and adsorption of dissolved nitrogen and phosphorus.

[0051] 3. Moisture-regulating and stabilizing zone A moisture retention and stability zone is set up downstream of the midstream nutrient interception zone in the mid-slope soil, such as... Figure 4 As shown, the zone includes a moisture-regulating and water-storing tank, a water-storing substrate layer, and a capillary water replenishment layer. The moisture-regulating and water-storing steady-state zone is used to retain incoming water during periods of water availability and to slowly release water to the downstream plant-microbe denitrification and purification zone under conditions of water shortage or no continuous water supply, thereby maintaining a moist environment in the plant rhizosphere and microbial attachment layer and reducing the risk of microbial activity decline.

[0052] The dimensions of the humidification and conditioning tank are 4.0m long, 0.80m wide, and 0.50m deep.

[0053] The water storage substrate layer is composed of a mixture of crushed stone, gravel, biochar and coconut coir in equal mass ratios, and the thickness of the water storage substrate layer is 0.30m.

[0054] The capillary water replenishment layer is composed of straw fiber felt and coconut coir fiber felt mixed in equal mass ratios, and the thickness of the capillary water replenishment layer is 0.03m.

[0055] 4. Gentle slope ecological interception dual purification ditch zone Ecological interception and dual-purification ditch belts are laid out on gentle slopes and at the confluence sections of slope toes, such as... Figure 5 As shown, the gentle slope ecological interception dual-purification ditch zone includes an ecological interception ditch connected to the downstream of the regulation and moisture retention steady-state zone. The ecological interception ditch serves as the main channel of the system, continuously connecting the outflow from each upstream zone with the inflow from each downstream zone. In this embodiment, the ecological interception ditch adopts a trapezoidal cross-section, with a bottom width of 0.60m, a depth of 0.70m, and a slope ratio of 1:1. A permeable stabilizing layer is laid at the bottom of the ditch. In this embodiment, the permeable stabilizing layer is composed of 0.15m thick gravel with a particle size of 40mm.

[0056] Along the water flow direction, a permeable deceleration and purification zone and a plant-microorganism denitrification and purification zone are sequentially set up within the ecological interception ditch. The permeable deceleration and purification zone consists of three subsurface flow dams spaced 4 meters apart along the water flow direction of the ecological interception ditch. Each subsurface flow dam contains a filter media layer with both permeability and adsorption functions. The filter media layer consists of a 0.15-meter-thick layer of fine sand and a 0.20-meter-thick layer of sandy planting soil above the fine sand layer, used to reduce flow velocity, increase residence time, and promote the sedimentation of particulate pollutants.

[0057] Emergent and submerged plants are placed in the plant-microbial denitrification and purification zone, which is filled with a carbon source matrix. In this embodiment, emergent and submerged plants are densely planted, with a coverage controlled at 70%. The plants planted in this embodiment are water celery and Vallisneria natans, with a planting density of 18 plants / m². 2The carbon source matrix is ​​a mixture of corn cobs, straw segments, and biochar granules of equal mass. Crushed agricultural waste carbon source is filled in the upper part of the fine sand layer or at the boundary between the fine sand layer and the sandy planting soil layer in the subsurface flow dam to continuously provide carbon source for denitrifying microorganisms. In this embodiment, crushed corn cobs are used as the crushed agricultural waste carbon source.

[0058] The plant rhizosphere, the pores of the filler, and the carbon source matrix together form an alternating aerobic-anoxic-anaerobic microenvironment, which allows nitrate nitrogen to be converted into nitrogen gas through denitrification, thereby reducing the nitrogen pollution load.

[0059] 5. Ecological pond reuse zone An ecological pond reuse zone is set up downstream of the ecological interception and double purification ditch zone on a gentle slope. This zone includes a sedimentation buffer zone, a plant purification zone, and a clear water storage zone, all connected in sequence. The purified effluent, after storage, can be reused for irrigation of sloping farmland, water replenishment for economic forests, or moisture conservation during the dry season. Specifically, in this embodiment, the ecological pond reuse zone is transformed from an existing low-lying pond at the foot of the slope. A safety overflow outlet and drainage channel are provided at the outlet side of the clear water storage zone.

[0060] The above-mentioned scheme was used to monitor its operational effectiveness. The results showed that the system of this invention can continuously reduce sediment and nitrogen and phosphorus pollutants in surface runoff and shallow interflow on sloping farmland. Specifically, the sediment or suspended solids reduction rate can reach 60%–80%, the nitrogen pollutant reduction rate can reach 35%–55%, and the phosphorus pollutant reduction rate can reach 30%–50%. The purified effluent, after being stored in an ecological pond, can be reused for irrigation of sloping farmland, water replenishment for economic forests, or moisture conservation during the dry season, improving water resource utilization efficiency by 20%–40%. Simultaneously, the system helps maintain a relatively stable microbial habitat and operational status during both water-bearing and dry periods. Thus, it balances non-point source pollution control, resource recycling, and system stability.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A five-belt, three-level, dual-circulation system for the prevention and control of surface-source pollution in sloping farmland, characterized in that, The slope of the farmland includes, from top to bottom, a steep slope source control zone, a medium slope soil nutrient interception zone, a water storage and moisture retention zone, a gentle slope ecological interception double purification ditch zone, and an ecological pond reuse zone. The steep slope source control zone is set up on slopes with a slope of 16° to 25°, and it has reverse slope steps along the contour lines. The medium-slope soil nutrient interception zone is laid on a slope section with a slope of 6° to 15°. It is provided with embedded adsorption ridges at intervals along the contour lines. The embedded adsorption ridges are provided with a through core groove along the length of the ridge, and the core groove is provided with an adsorption material layer. The regulating and moisturizing steady-state zone is provided with a regulating and moisturizing tank, and the regulating and moisturizing tank is provided with a capillary water replenishment layer and a water storage matrix layer from bottom to top; The gentle slope ecological interception dual purification ditch zone is laid in a gentle slope area or slope toe confluence area with a slope of no more than 6°, including an ecological interception ditch connected to the downstream of the regulation and moisture retention steady state zone. The ecological interception ditch is arranged in sequence along the water flow direction as a water-permeable deceleration purification zone and a plant-microorganism denitrification purification zone. The ecological pond reuse zone is sequentially equipped with a sedimentation buffer zone, a plant purification zone, and a clear water storage zone.

2. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The reverse slope step has a step width of 1.5m to 2.5m, and the step surface forms a reverse slope angle of 5° to 10° on the inner side of the slope. The outer edge of the reverse slope step is provided with a low embankment or vegetation stabilization strip.

3. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The height of the embedded adsorption embankment is 0.40m to 0.80m, and the top width is 0.30m to 0.60m. The embedded adsorption embankment is provided with a through core groove along the length of the embankment. The width of the core groove is 0.25m to 0.35m and the depth is 0.35m to 0.45m. The water-facing side of the core groove is provided with a flow-guiding and seepage-blocking layer made of compacted clay with a thickness of 0.10m to 0.20m. The medium-slope soil nutrient interception zone is equipped with no less than two embedded adsorption ridges, with a slope spacing of 15m to 25m between adjacent embedded adsorption ridges; when the slope is 6° to 10°, the slope spacing is 20m to 25m; when the slope is 10° to 15°, the slope spacing is 15m to 20m.

4. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The adsorption material layer consists of a gravel flow guiding layer, a zeolite adsorption layer, a biochar adsorption layer, and a soil covering layer from bottom to top. The gravel diversion layer has a thickness of 0.08m to 0.15m, the zeolite adsorption layer has a thickness of 0.08m to 0.15m, the biochar adsorption layer has a thickness of 0.08m to 0.12m, and the soil cover layer has a thickness of 0.05m to 0.10m.

5. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The water storage substrate layer is composed of one or more of the following: crushed stone, gravel, biochar, coconut coir, and straw fiber blanket.

6. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, Within the permeable deceleration and purification zone, subsurface flow dams are installed at intervals of 4m to 8m along the water flow direction of the ecological interception ditch; the subsurface flow dams are filled with a filter material layer, which consists of a fine sand layer and a sandy planting soil layer located above the fine sand layer. The upper part of the fine sand layer, or the boundary between the fine sand layer and the sandy planting soil layer, is filled with a carbon source of crushed agricultural waste; the carbon source of agricultural waste is one or more of straw, corn cob, and rice husk.

7. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The plant-microbial denitrification and purification zone is equipped with emergent and submerged plants and filled with a carbon source matrix, which is composed of one or more of the following: corn cobs, straw segments, sawdust, and biochar particles.

8. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The ecological interception ditch is continuously laid along the gentle slope area, the toe of the slope confluence area and the downstream connecting section; the ecological interception ditch adopts a trapezoidal cross section, with a bottom width of 0.6 to 1.0 m, a ditch depth of 0.5 to 0.8 m, a side slope ratio of 1:1 to 1.5, and a permeable stable bottom layer laid at the bottom of the ditch.

9. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, The ecological pond reuse zone is formed by transforming low-lying pits, abandoned ponds, or farmland edges.

10. The five-belt, three-level, dual-circulation sloping farmland surface pollution control system according to claim 1, characterized in that, At least one of the following: the water storage and moisture retention steady-state zone, the ecological interception ditch, and the ecological pond reuse zone is equipped with a safety overflow outlet and a drainage channel.

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