Method for planting mangrove forest in sandy soil by using microtopography transformation and water control technology

Abstract

The invention discloses a method for planting a mangrove forest in sandy soil by using a microtopography transformation and water control technology, and solves the repair problems of poor water and fertilizer retention of the sandy soil, insufficient mangrove forest flooding time and the like. The method comprises the following steps: calculating the size (depth, width and gradient) of a tidal creek based on a tidal cycle, selecting a latticed, radial and fishbone-shaped layout mode, excavating the tidal creek to form a three-area spatial layout of a planting area, the tidal creek and a light beach; a water control facility comprising a gate and a liquid level controller is installed, and a water level threshold value is set to control the single-day flooding duration to be larger than or equal to 3 hours; experimental data show that the one-year survival rate of the sandy soil mangrove forest reaches 86% through the method and is greatly improved compared with a traditional method, soil organic carbon is improved, the nursery stock complementary planting rate is reduced by about 10%, ecological benefits and engineering economy are both achieved, and a scientific and efficient technical scheme is provided for restoring the coastal sandy soil mangrove forest.

Description

Technical Field

[0001] The present invention relates to the technical field of mangrove ecological restoration, and in particular to a method for planting mangroves in sandy soil by utilizing micro-topography transformation and water control technology. The method is suitable for mangrove wetland ecological restoration projects in coastal sandy soil areas. Background Art

[0002] Mangroves are important coastal wetland ecosystems, providing multiple ecological functions, including wind and wave protection, carbon sequestration, and biodiversity maintenance. However, with increasing human activity, mangroves are facing challenges such as shrinking area and habitat degradation. In areas with sandy soils, mangrove cultivation is extremely difficult due to their loose structure, poor aeration and permeability, poor water and nutrient retention, low nutrient content, and susceptibility to tidal leaching.

[0003] Traditional mangrove planting methods face numerous challenges in sandy soils. For example, direct planting can hinder root anchorage, leading to insufficient water and nutrient supply and low survival rates. Some areas use planting bags and deep planting, but this approach suffers from a single tree species and limited biodiversity. Large-scale excavation and backfilling methods are not only labor-intensive and costly, but can also easily cause soil erosion and sediment spread, impacting surrounding aquatic environments.

[0004] In mangrove ecological restoration, the surface silt in mangrove planting areas is thin, and in some areas, the bottom is heavily weathered tuff. Traditional methods require excavation and backfilling with planting soil, which is labor-intensive and expensive. In the Blue Bay Comprehensive Renovation Project in Wenchang City, Hainan Province, the bottom of the aquaculture ponds in the mangrove restoration area is mostly sandy and low in organic matter. Furthermore, the landward-facing aquaculture ponds are not directly connected to Bamen Bay, resulting in insufficient flooding time. Traditional methods are unable to effectively address these issues.

[0005] Patent CN202410914673.1 discloses a method of improving the root growth environment and drought resistance by transforming the micro-topography of deep and shallow interval water storage ditches and improving the soil in planting holes, using fine sand and manure, and combining them with bare-root seedlings of drought-resistant shrubs, including planting Siberian Nitraria in deep ditches and Haloxylon ammodendron in shallow ditches, with appropriate species configuration patterns and less irrigation measures. However, this method simply processes the ditches without combining the characteristics of tides with the distribution of ditches, resulting in a low survival rate of vegetation species and poor growth.

[0006] Therefore, there is an urgent need for a mangrove planting method tailored to the characteristics of sandy soil to increase the survival rate of seedlings, improve habitat conditions, and achieve effective restoration of the mangrove ecosystem. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for planting mangroves in sandy soil using micro-topography modification and water control technology. According to the relationship between the tidal cycle, the size of the tidal gully is calculated and the layout pattern of the tidal gully is clarified. By optimizing the topography and hydrological conditions of the planting area, the problems of poor water and fertilizer retention in sandy soil and insufficient flooding time are solved, the survival rate and growth quality of mangrove seedlings are improved, and the efficiency and sustainability of mangrove ecological restoration in sandy soil areas are achieved.

[0008] To achieve the above object, the present invention provides a method for planting mangroves in sandy soil using micro-topography transformation and water control technology, which is characterized by comprising the following steps: (1) Clearing obstacles and invasive species in sandy soil areas; (2) Based on the relationship between the tidal cycle, the size of the tidal ditch and the layout pattern of the tidal ditch are calculated. The tidal ditch is excavated based on the obtained size and layout pattern, forming a three-zone spatial layout of planting area, tidal ditch and light beach; (3) Install water control facilities to connect the water systems inside and outside the restoration area; (4) Backfill the planting holes with sea mud and plant mangrove seedlings; (5) Fix and regularly tend the seedlings.

[0009] Furthermore, the dimensions of the tidal gully include maximum width, depth, and slope; and the layout pattern includes grid, radial, or fishbone layout.

[0010] Furthermore, the calculation formula for the tidal gully depth D is: ; : local mean tidal range, in meters, obtained through long-term observations or tidal forecasts; : Maximum flow velocity at low tide, in m / s, which needs to be calculated based on measured tidal flow velocity data or hydrodynamic models; : the shortest duration of ebb tide, in seconds; S: tidal creek slope, dimensionless; ; : average flow velocity at low tide, in m / s; : the average duration of ebb tide, unit: s; n: Manning roughness coefficient, 0.025-0.03 for sandy soil; R: hydraulic radius, unit: m, approximately the cross-sectional area of the wet ditch divided by the length of the wet perimeter. The depth D of the ditch is calculated using the local average tidal range, the maximum flow rate at the ebb tide, and the shortest duration of the ebb tide. The core purpose is to accurately design the depth of the tidal ditch based on the principle of tidal hydrodynamics, to solve the problems of insufficient inundation time and exposed root system of mangroves in sandy soil, to create a suitable growth environment for mangroves, and to ensure that there is still 0.3-0.5 meters of water depth in the tidal ditch at the lowest tide level, meeting the root respiration needs of mangroves, avoiding root exposure in the air due to low water level, and affecting normal growth. The depth of the tidal ditch needs to exceed the root depth of the mangrove seedlings to prevent the roots from being exposed due to soil erosion or water level drop when the tide recedes, and to provide stable growth space for the root system of the seedlings. This design can effectively reduce the death of seedlings due to root damage and improve the survival rate of planting. The depth calculation combined with the ebb flow rate and time parameters can reasonably design the slope S of the tidal ditch to ensure that the tidal water is quickly discharged when the tide recedes, avoiding water accumulation; at the same time, it avoids excessive erosion of the water flow to the slope of the tidal ditch due to excessive slope, maintaining the stability of the structure of the tidal ditch. Precise depth design combined with tidal ditch layout and water control technology can improve the water and fertilizer retention capacity of sandy soil, promote soil organic carbon accumulation and nutrient improvement. Scientific calculation avoids large-scale earthwork excavation and backfill in traditional methods, reduces engineering quantity and construction cost, and reduces the disturbance to the surrounding environment.

[0011] Further, the calculation formula of the maximum width W of the tidal ditch is: ; : the maximum flow rate at the peak of ebb tide (m / s), which can be estimated by the tidal flow rate and the cross-sectional area of the ditch; 3 : the average flow rate at the ebb tide (m / s), taken as : the average flow rate at the ebb tide (m / s), taken as 50%-70% of the total tidal flow; d: effective tidal creek depth (m), which is D minus the thickness of the silt layer. The maximum tidal creek width W is calculated using the maximum flow at peak ebb tide, the average flow velocity at ebb tide, and the effective tidal creek depth. The core objective is to accurately design the tidal creek width based on hydrodynamic principles to balance tidal flow and velocity, preventing siltation or excessive scouring in sandy soils and thus creating a stable hydrological environment for mangroves. The tidal creek width must match the tidal flow and velocity. The above formula ensures that water flows through the tidal creek at a reasonable rate during ebb tide, avoiding excessive flow velocity and soil scouring due to a narrow width, or excessive flow velocity and sediment accumulation due to a wide width. Sandy soils have a loose structure and are easily eroded by water. Accurately calculating the width prevents tidal creek collapse due to scouring or poor drainage due to siltation, thereby maintaining long-term stability and ensuring the flooded conditions necessary for mangrove growth. If the width is too small, the high flow velocity at low tide will exacerbate scouring of sandy soils, leading to tidal gully slope collapse and soil loss. If the width is too large, the low flow velocity will fail to remove suspended sediment, causing siltation in the gully and compromising drainage and inundation efficiency. Using the above formula, the gully width can be matched to the flow rate and velocity, maintaining an "erosion-siltation" balance. Calculating tidal gully width using flow rate, velocity, and depth parameters essentially combines hydrodynamic principles with sandy soil characteristics to achieve "precision design" of the tidal gully system. Its core value lies in balancing hydrological processes with soil stability, creating a suitable inundation environment and growth substrate for mangroves, ultimately improving the efficiency and sustainability of ecological restoration.

[0012] Furthermore, it is clear that the tidal gully layout pattern is determined by the layout pattern decision index. ; is the layout mode decision index; A is the area of ​​the repair area, in m 2 ; is the shape coefficient of the repair area, which is 1 for rectangles and 0.7-0.9 for irregular shapes; : local average tidal range (m); is the tidal type correction factor (1.0 for semi-diurnal tides and 0.8 for diurnal tides); >1.5, select radial layout; 0.8< ≤1.5, select grid layout; ≤0.8, select fishbone layout.

[0013] Furthermore, the water control facilities installed in step (3) include a gate, a liquid level controller, a solenoid valve, a connecting pipe and a filter pipe. The water level threshold is set by the liquid level controller to automatically control the connection between the external seawater and the water body in the aquaculture pond to ensure the flooding time of the mangroves.

[0014] Furthermore, the planting hole in step (4) has a size of 30 cm × 30 cm × 30 cm, and the organic carbon content of the backfilled sea mud is ≥ 5 g / kg, and the salinity is < 25‰.

[0015] Furthermore, in step (4), the seedlings planted are selected from at least two of Tung Tree, Mangrove Tree, and Bruguiera gymnorrhiza, with a plant spacing of 2-4 m.

[0016] Furthermore, in step (5), a bamboo pole is used to fix the seedlings, the bamboo pole is inserted into the soil to a depth of ≥50 cm, and is tied and connected to the main trunk of the seedlings.

[0017] Furthermore, the lower limit of the water level threshold is the mean sea level + 0.3 m, the upper limit is the mean sea level + 0.8 m, and 3 hours < single-day flooding duration < 12 hours.

[0018] Beneficial effects of the present invention: Based on the tidal cycle and hydrodynamic principles, the depth D, width W and slope S of the tidal ditch are accurately calculated through formulas to ensure that the tidal ditch depth meets the inundation requirements of mangroves, the slope balances drainage efficiency and anti-erosion ability, and the width adapts to tidal flow to avoid siltation or scouring; the layout pattern decision index is introduced, and the grid, radial or fishbone layout is scientifically selected according to the tidal range, the shape of the restoration area and the tidal type to improve the matching degree between the tidal ditch system and the terrain; the water level threshold is automatically adjusted through facilities such as liquid level controllers and solenoid valves, and the daily inundation time is accurately controlled to be ≥3 hours, solving the core problems of water retention in sandy soil and insufficient inundation time.

[0019] There's no need for large-scale excavation and backfilling, which reduces the amount of work and construction costs compared to traditional methods. It also avoids soil erosion and sediment spread, aligning with the concept of green construction. By utilizing local marine mud and tidal energy, the transportation of imported soil and energy consumption are reduced, enabling the localized recycling of restoration materials. Different from the traditional "excavation and filling to improve soil" or "single water control" model, this three-dimensional restoration technology of "micro-topography modification + tidal linkage + composite matrix" addresses the multiple challenges of poor water and fertilizer retention in sandy soil, difficulty in root colonization, and insufficient flooding time. Through formulaic design and quantitative parameters, a replicable standardized technical process is constructed, significantly improving the scientific nature and engineering feasibility of mangrove restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an actual map of sandy soil.

[0021] Figure 2 It is a micro-topography transformation map.

[0022] Figure 3 Diagram of water control technology facilities.

[0023] Figure 4 This is a map of sea mud backfill. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The following embodiments are not intended to limit the present invention but are merely intended to illustrate the present invention.

[0025] In the specific embodiments, steps, material selections, and numerical parameters that are not described in detail are all conventional choices in the prior art or any currently disclosed prior art.

[0026] 1. Experimental Location and Materials Location: An aquaculture pond in Wenchang City, Hainan Province (sandy soil, organic carbon content 0.46 g / kg, salinity 20‰, tidal range 2.5 m, semi-diurnal tide).

[0027] Material: Seedlings: Tung tree, Red sea olive, seedling height 50-60cm, ground diameter 1.0-1.2cm.

[0028] Equipment: amphibious excavator, liquid level controller, connecting pipe (diameter 250mm), soil sampler.

[0029] 2. Experimental Grouping Example

[0030] (1) Calculation of tidal gully depth D: The formula is ; : Local average tidal range, taken from Wenchang data, =2.5m; : Maximum velocity at low tide, in m / s. Estimated based on tidal characteristics in Wenchang area, semi-diurnal tide, tidal range of 2.5m, measured or hydrodynamic model data =0.5m / s; : The shortest duration of low tide, in seconds (s). The semi-diurnal tidal cycle is about 12.4 hours, and the shortest duration of low tide is 4 hours. =4×3600=14400s.

[0031] The calculated depth is D=1.25+0.575≈1.8m.

[0032] (2) Calculation of the maximum width W of the tidal gully: The formula is ; : Maximum flow during the ebb tide peak, unit: m 3 / s, the tidal flow of Wenchang aquaculture pond is small, =1.0m 3 / s; : Average velocity at low tide, in m / s. Take half of the maximum tidal velocity, =0.5m / s, that is =0.5×0.5=0.25m / s; d: effective water depth, unit: m, d=D-thickness of sediment layer, D=1.8m, thickness of sediment layer is 0.2m, so d=1.8-0.2=1.6m; W≈2.5m.

[0033] (3) Calculation of tidal gully slope S: formula: ; : Average velocity at low tide, in m / s. Calculated in the same way as width, =0.2m / s; : Average duration of ebb tide, in seconds (s). The semi-diurnal tide is averaged over 6 hours. =6×3600=21600s; n: Manning's roughness coefficient, for sandy soil, n=0.027; R: hydraulic radius, in m. The cross section of the tidal ditch is approximately rectangular, with a width of w = 2.5 m and a depth of D = 1.8 m. Cross-sectional area A = 2.5 * 1.8 ≈ 4.5 m 2 ; The wet perimeter length P = 2D + W ≈ 6.1 m, so R = A / P ≈ 0.74; The calculation results show that S=(0.25×21600×0.000729) / 15×0.74≈0.35.

[0034] (4) Calculation of layout mode decision index: formula: ; Tidal range Δh = 2.5 m (semi-diurnal tide); Tidal type correction factor =1.0 (semi-diurnal tide); Area A = 5.2 hectares, approximately 52,000 m 2 , shape factor =1.0(rectangular area); Calculated =(1×(2.5) 2 ×10000) / 52000 ≈1.2.

[0035] Comparative Example 1: Use the traditional planting bag deep planting method.

[0036] Comparative Example 2: Use large-area earth backfill method.

[0037] The key calculation parameters of Example 1 and Comparative Examples 1-2 are as follows:

[0038] 2. Experimental steps 1. Example operation: After clearing the site, calculate the tidal gully dimensions according to a formula and excavate the site, creating a layout consisting of a planting area (60%), a tidal gully (25%), and a bare beach (15%). Water control systems were installed, and water level thresholds were set to ensure daily flooding for ≥4 hours. Planting holes were 30 cm × 30 cm × 30 cm, backfilled with 30 cm of sea mud, and secured with bamboo poles after planting.

[0039] 2. Comparative operation: Comparative Example 1: After leveling the site, place planting bags (containing nutrient soil) directly in the planting holes, and plant seedlings deep without tidal ditches or water control facilities.

[0040] Comparative Example 2: Mechanically excavate sandy soil to a depth of 0.3m, backfill with planting soil to the original elevation, no tidal ditch, relying on natural tides.

[0041] 3. Observation Indicators and Data 1. Survival rate (1-year cycle)

[0042] The survival rate of the embodiment is significantly higher than that of the control example, indicating that the micro-topography and water control technology effectively improve the root environment and reduce tidal erosion and drought stress.

[0043] 2. Growth indicators (1-year growth)

[0044] The plant height and ground diameter of Example 2 increased by 68% and 31% respectively compared with those of Example 2, indicating that the stable hydrological conditions and high-fertility sea mud provided by the tidal creek system promoted the growth of seedlings.

[0045] 3. Soil physical and chemical properties (0-20cm soil layer)

[0046] The soil organic carbon, total nitrogen and total phosphorus contents of the example were increased by 35.22%, 34.17% and 22.35% compared with the initial values, respectively, which were significantly better than those of the control example, indicating that sea mud backfilling and tidal gully siltation effectively improved soil fertility.

[0047] Overall, this method, through tidal gully microtopography modification and intelligent water control, has increased the survival rate of mangroves on sandy soil from 59%-67.5% (using traditional methods) to 86%, achieving an annual increase in plant height of ≥50% and an annual increase in ground diameter of ≥30%, significantly outperforming the control group. The combination of sea mud backfill and tidal gully siltation significantly increases soil organic carbon and nutrient content, optimizes salinity, and provides a suitable growth medium for mangroves.

[0048] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for planting mangroves in sandy soil using micro-topography transformation and water control technology, characterized in that: The following steps are involved: (1) Clearing obstacles and invasive species in sandy soil areas; (2) Based on the relationship between the tidal cycle, the size of the tidal ditch and the layout pattern of the tidal ditch are calculated. The tidal ditch is excavated based on the obtained size and layout pattern, forming a three-zone spatial layout of planting area, tidal ditch and light beach; (3) Install water control facilities to connect the water systems inside and outside the restoration area; (4) Backfill the planting holes with sea mud and plant mangrove seedlings; (5) Fix and regularly tend the seedlings.

2. The method according to claim 1, characterized in that The dimensions of tidal gullies include maximum width, depth, and slope; layout patterns include grid, radial, or herringbone layouts.

3. The method according to claim 2, characterized in that The calculation formula for tidal creek depth D is: ； : local mean tidal range, in meters, obtained through long-term observations or tidal forecasts; : Maximum flow velocity at low tide, in m / s, which needs to be calculated based on measured tidal flow velocity data or hydrodynamic models; : the shortest duration of low tide, in seconds; S: tidal creek slope, dimensionless; ; : average flow velocity at low tide, in m / s; : average duration of ebb tide, in seconds; n: Manning roughness coefficient, which is 0.025-0.03 for sandy soil; R: hydraulic radius, in meters, which is approximately the cross-sectional area of ​​the tidal gully divided by the wetted perimeter.

4. The method according to claim 1, wherein The calculation formula for the maximum width W of the tidal creek is: ; : Maximum flow during the ebb tide peak, in m 3 / s, which can be estimated by tidal velocity and cross-sectional area of ​​tidal channel; : Average velocity at low tide, in m / s, 50%-70%; d: Effective water depth of tidal creek, in meters, i.e. D minus the thickness of the silt layer.

5. The method according to claim 1, wherein The layout pattern of the tidal gully is determined by the layout pattern decision index. ; is the layout mode decision index; A is the area of ​​the repair area, in m 2 ; is the shape coefficient of the repair area, which is 1 for rectangles and 0.7-0.9 for irregular shapes; : local average tidal range, in meters; is the tidal type correction factor, which is 1.0 for semi-diurnal tides and 0.8 for diurnal tides; >1.5, select radial layout; 0.8< ≤1.5, select grid layout; ≤0.8, select fishbone layout.

6. The method according to claim 1, characterized in that The water control facilities installed in step (3) include a gate, a liquid level controller, a solenoid valve, a connecting pipe and a filter pipe. The water level threshold is set by the liquid level controller to automatically control the connection between the external seawater and the water body in the aquaculture pond to ensure the flooding time of the mangroves.

7. The method according to claim 1, characterized in that The planting hole size in step (4) is 30 cm×30 cm×30 cm, and the organic carbon content of the backfilled sea mud is ≥5 g / kg and the salinity is <25‰.

8. The method according to claim 1, characterized in that In the step (4), the planted seedlings are selected from at least two of the group consisting of Tung Tree, Mangrove Tree, and Bruguiera gymnorrhiza, with a plant spacing of 2-4 m.

9. The method according to claim 1, characterized in that In step (5), bamboo poles are used to fix the seedlings. The bamboo poles are inserted into the soil to a depth of ≥50 cm and are tied and connected to the trunks of the seedlings.

10. The method according to claim 6, characterized in that The lower limit of the water level threshold is the mean sea level + 0.3m, the upper limit is the mean sea level + 0.8m, and the flooding duration in a single day is 3 hours < 12 hours.

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