A submerged plant seed propagation method based on sediment reuse

Abstract

The application provides a submerged plant seed propagation method based on bottom mud recycling. The bottom mud generated by dredging is dehydrated and solidified, an oxidizing agent is added thereto and mixed, and air-dried; the bottom mud is sieved and classified into coarse-grained soil, medium-grained soil and fine-grained soil, the fine-grained soil is uniformly mixed with inorganic mineral fillers to obtain a seed filling agent, and the medium-grained soil, fly ash, biomass and microbial conditioner are uniformly mixed to obtain a seed growth base; the submerged plant seeds are mixed with the seed filling agent for granulation to prepare primary pelletized seeds; the primary pelletized seeds are mixed with the seed growth base and coarse-grained soil for secondary granulation to prepare secondary pelletized seeds; and the secondary pelletized seeds after secondary granulation are scattered in a target restoration water area for submerged plant community restoration. The application is beneficial to the recycling and resource utilization of contaminated bottom mud, can replace the exogenous clean lake mud or soil required in the prior art, provides a new substrate source for submerged plant planting, especially seed introduction, and saves soil resources.

Description

Technical Field

[0001] This invention relates to the field of seed propagation, specifically to a method for propagating submerged plant seeds. Background Technology

[0002] As primary producers in aquatic ecosystems, the restoration and health of submerged plant communities are considered key factors affecting the construction and stability of aquatic ecosystems. However, with rapid socio-economic development, large amounts of nitrogen and phosphorus have entered lakes, causing severe eutrophication and gradually leading to the degradation of submerged plant communities and the loss of seed banks. Currently, the commonly used introduction methods for submerged plant restoration can be divided into two main categories: asexual reproduction and sexual reproduction. Among them, seeds produced by sexual reproduction of submerged plants have advantages such as small size, large quantity, and easy transport. However, seed propagation also faces many problems in practice, such as difficulty in planting after sowing, feeding by aquatic animals, and disturbance from wind and waves, making it difficult to control the germination rate, survival rate, and coverage after sowing. In addition, long-term eutrophication of water bodies can also lead to serious endogenous pollution. The characteristics of polluted sediment—high organic matter, high water content, and low strength—are not conducive to the root anchoring and seedling growth of submerged plant seeds after germination.

[0003] To address the aforementioned issues, CN 105265055 B discloses a method for rapid propagation and colony establishment of *Vallisneria natans* seeds. This method utilizes clay to granulate the *Vallisneria natans* seeds, allowing for uniform sowing in large bodies of water and significantly improving seed survival rates. CN 103636428 B discloses a submerged plant growth bag and its manufacturing and application methods. By configuring river sand and lake mud as growth substrates within the growth bag, it promotes the growth of submerged plants in waters where bottom sediment substrates cannot meet growth requirements. CN 105993260 B discloses a method for restoring degraded wetland vegetation using improved wetland soil seed banks. This method involves covering the degraded wetland with improved seed bank soil, allowing for natural germination and vegetation formation. In all of these methods, whether pelleting, using plant bags, or covering with topsoil, exogenous bottom sediment or soil is used as an auxiliary substrate for the introduction of submerged plant seeds. However, the extensive use of exogenous sediment or soil may cause varying degrees of damage to their original habitats, while the seed bank carried in the cleaned sediment or soil may also interfere with the introduction and restoration of submerged plants.

[0004] All of the methods mentioned above, whether pelleting, using plant bags, or covering with topsoil, rely on exogenous clean sediment or soil as a substrate for the introduction of submerged plant seeds. However, the extensive use of exogenous sediment or soil may cause varying degrees of damage to the original habitat, and the seed bank originally carried in the sediment or soil may also interfere with the restoration of submerged plant introductions.

[0005] On the other hand, in order to reduce endogenous nutrient load and improve plant growth conditions, many lakes carry out bottom sediment dredging before planting. However, if the polluted bottom sediment generated from dredging is dumped indiscriminately in the environment without treatment, it can easily cause environmental pollution. Therefore, currently, polluted bottom sediment is often transported to designated disposal sites for treatment or landfill. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies by providing a method for seed propagation of submerged plants based on the reuse of bottom sediment. On the one hand, by performing secondary pelleting and other measures on the seeds, the survival rate of seed propagation and seedlings of submerged plants can be improved. On the other hand, by treating and reusing the dredged bottom sediment generated from dredging, the problem of subsequent treatment and utilization of dredged bottom sediment can be solved, and the current situation of relying heavily on external soil in existing seed propagation technologies for submerged plants can be improved.

[0007] Technical solution: The present invention provides a method for propagating submerged plant seeds based on sediment recycling, comprising the following steps:

[0008] S1. Dehydrate and solidify the bottom mud generated from dredging, add oxidant and mix, air dry, and then crush and remove impurities.

[0009] S2. The sediment obtained in step S1 is sieved and classified into coarse soil (2-5mm), medium soil (0.05-2mm), and fine soil (less than 0.05mm) according to the sediment particle size. The fine soil is uniformly mixed with inorganic mineral filler to obtain seed filler, and the medium soil, fly ash, biomass and microbial conditioner are uniformly mixed to obtain seed growth substrate.

[0010] S3. Mix the submerged plant seeds with the seed filler and granulate them to make primary pelleted seeds;

[0011] S4. The primary pelleted seeds are mixed with seed growth substrate and coarse soil for secondary granulation to produce secondary pelleted seeds.

[0012] S5. The secondary pelleted seeds after secondary granulation are scattered in the target remediation water area to restore the submerged plant community.

[0013] Furthermore, the dewatering and solidification method in step S1 is determined according to the dredging method: the bottom mud generated by bucket dredging is dewatered by sun drying and tilling; the bottom mud generated by cutter suction dredging is dewatered and solidified by belt filter press, and the moisture content of the solidified bottom mud is controlled between 35% and 50%.

[0014] Furthermore, the oxidant in step S1 includes calcium hypochlorite, calcium nitrate, or calcium peroxide, and the application rate of the oxidant is 2.5-5 g / kg of the bottom sediment.

[0015] Further, the inorganic mineral filler in step S2 includes vermiculite, fly ash and sepiolite that have been physically crushed and passed through a 200-mesh sieve, with a mixing weight ratio of 1:1:1; fine soil and inorganic mineral filler are uniformly mixed in a weight ratio of 55-65:35-45 to obtain seed filler.

[0016] Further, the fly ash mentioned in step S2 is obtained by crushing and passing it through a 2mm sieve; the biomass is obtained by drying and crushing reed stalks and then passing them through a 2mm sieve; the microbial conditioner includes Bacillus subtilis, Bacillus mucilaginosus, Nocardia fibrosis, Lactobacillus plantarum, and Thiobacillus denitrification, mixed in equal parts by weight; medium-grained soil, fly ash, biomass, and microbial conditioner are uniformly mixed in parts by weight of 50-60:20-30:10-20:0.1-0.5 to obtain a seed growth medium.

[0017] Furthermore, the submerged plant seeds mentioned in step S3 include seeds of Vallisneria natans, Myriophyllum spicatum, Hydrilla verticillata, Elodea nuttallii, and Potamogeton crispus. These seeds are mixed with seed filler in a weight ratio of 1:6-8 and granulated to produce individual primary pelleted seeds.

[0018] Furthermore, during the granulation process of mixing submerged plant seeds with seed filler, a chitosan solution with a concentration of 0.5-1.5% is sprayed evenly by atomization to ensure that the seed filler tightly coats the surface of the submerged plant seeds. The amount of chitosan solution sprayed is 1-2% of the mass of the seed filler.

[0019] Further, in step S4, the primary pelleted seeds, seed growth substrate, and coarse soil are mixed and granulated a second time at a weight ratio of 1:50-60:10-20.

[0020] Furthermore, the particle size of the primary pelleted seeds in step S3 is 0.3-0.6 cm, and the particle size of the secondary pelleted seeds in step S4 is 4-8 cm.

[0021] Further, in step S4, the secondary mixing and granulation uses 10-20 primary pelleted seeds. During the mixing and granulation of the primary pelleted seeds and the seed growth medium, a chitosan solution with a concentration of 0.5-1.5% is sprayed by atomization, and the amount of chitosan solution is 1-2% of the mass of the seed growth medium. Then, coarse soil is added and mixed and granulated. During the mixing and granulation, a chitosan solution with a concentration of 0.5-1.5% is sprayed by atomization, and the amount of chitosan solution is 1-2% of the mass of the coarse soil. This process yields secondary pelleted seeds.

[0022] Beneficial effects: 1. This invention reduces the water content of polluted bottom sediment in eutrophic water bodies by solidification and dehydration, chemical oxidation, and sun-drying and tilling. It can also remove and reduce the excessive organic matter in the bottom sediment, which is conducive to the recycling and resource utilization of polluted bottom sediment. It can replace the external clean lake mud or soil required in the existing technology, and provides a new substrate source for the planting of submerged plants, especially for seed introduction, thus saving soil resources.

[0023] 2. This invention utilizes recycled sediment to granulate seeds twice, increasing the overall seed weight, reducing disturbance from wind, waves, and water flow, and improving settling speed and placement accuracy during seed dispersal. The abundant nitrogen and phosphorus nutrients in the sediment provide nourishment for seedling growth after germination. Microbial conditioners provide beneficial microorganisms for seed germination and seedling growth, promoting nutrient turnover within the growth medium. Using reed powder as biomass provides organic matter for seedlings while improving the physical structure of the seed growth medium, increasing its permeability and facilitating the penetration of external moisture. Chitosan solution acts as a binder, enhancing the stress resistance of seeds and seedlings, and positively promoting microbial activity.

[0024] 3. Different particle sizes of sediment and inorganic mineral fillers can play different roles through combination. Small-particle-size materials used in primary pelleting can increase the physical resistance of pelleted seeds and more evenly coat the seeds, while large-particle-size materials used in secondary pelleting increase the porosity of pelleted seeds, which is beneficial for the exchange of water and gas.

[0025] 4. This invention effectively solves the problems of seeds being easily affected by the external environment and having a low success rate of germination and transplanting. It can improve the survival rate of seeds and seedlings, and the pelleted seeds are also easy to carry and store. Detailed Implementation

[0026] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0027] Example 1: A method for propagating submerged plant seeds based on sediment recycling was implemented in a lake in Nanjing City, with a surface area of ​​approximately 3.7 km². 2 With an average depth of approximately 1.14 meters, it is a typical shallow urban lake. Taking the eastern part of Beihu Lake as an example, the overall water quality in the area is between Class IV and Class V, with sparse submerged plants, a monotonous water landscape, and low transparency. Affected by flood discharge and rainfall during the flood season, a large amount of pollutants are eventually deposited on the lake bottom under the action of water flow. The main physicochemical indicators of the lake bottom sediment are shown in Table 1. In May 2021, a backhoe dredger was used for dredging operations while the lake was still submerged, and the dredged bottom sediment was transferred to the shore.

[0028] Table 1 Physicochemical characteristics of bottom sediment in a certain lake area in eastern Hubei Province

[0029]

[0030] A sediment storage area was designated in the vacant land around the lake. The dredged sediment was then dried and tilled, and after about 4-5 days, the moisture content of the sediment decreased to about 50%. At this point, calcium peroxide was applied to the surface of the sediment at a dosage of 2.5 g / kg, and the mixture was thoroughly stirred to ensure thorough mixing. After the sediment was completely air-dried, it was crushed and sieved to remove biological residues, stones, garbage, and other impurities.

[0031] The crushed bottom mud was screened according to particle size into coarse soil (2-5mm), medium soil (0.05-2mm), and fine soil (<0.05mm). The fine soil was uniformly mixed with inorganic mineral filler at a weight ratio of 6:4 to obtain the seed filler. The medium soil, fly ash, biomass, and microbial conditioner were uniformly mixed at a weight ratio of 50:20:20:0.1 to obtain the seed growth medium. The inorganic mineral filler was prepared by mixing vermiculite, fly ash, and sepiolite in equal parts by weight after physical crushing and passing through a 200-mesh (0.074mm) sieve; the fly ash in the seed growth medium was obtained by crushing and passing through a 2mm sieve; the biomass was obtained by drying and crushing reed stalks and passing through a 2mm sieve; the microbial conditioner included Bacillus subtilis, Bacillus mucilaginosus, Nocardia fibrosis, Lactobacillus plantarum, and Thiobacillus denitrification, prepared by mixing equal parts by weight.

[0032] The seeds of Vallisneria natans, Elodea spp., and Myriophyllum spicatum were mixed with seed fillers and granulated using a granulator, with a seed-to-filler weight ratio of 1:6 for each type. During granulation, the submerged plant seeds were first placed into the granulator and the granulator was turned on. The seed filler was then divided into three equal portions and added to the granulator in three separate additions. After each addition, the seeds and filler were allowed to mix thoroughly before adding the next batch. During this process, a 0.5% chitosan solution was atomized and sprayed to promote thorough adhesion between the submerged plant seeds and the filler. The amount of chitosan solution sprayed was 1% of the mass of the seed filler, i.e., 1 ml of chitosan solution was atomized and sprayed for every 100g of seed filler and seeds during granulation. The final product consisted of three types of primary pelleted seeds with particle sizes of 0.4cm, 0.4cm, and 0.3cm, respectively.

[0033] Take 15, 15, and 20 primary pelleted seeds of *Vallisneria natans*, *Hydrilla verticillata*, and *Myriophyllum spicatum*, respectively. Mix the primary pelleted seeds with seed growth medium and coarse soil at a weight ratio of 1:50:10 for secondary pelleting. During pelleting, first add the primary pelleted seeds and seed growth medium to the granulator. After starting the granulator, atomize and spray chitosan solution to thoroughly mix the primary pelleted seeds and seed growth medium into spherical shapes. Then, add coarse soil and atomize and spray chitosan solution, continuing the granulation process. The amount of chitosan solution used during this process is 1.5% of the weight of the seed growth medium / coarse soil. The final product is secondary pelleted seeds with a particle size of approximately 4 cm, which are then stored in a cool, ventilated place.

[0034] In June 2022, a 10×10m permeable enclosure was constructed using silk netting in the eastern waters of the lake in Hubei Province. The average water depth within the enclosure was 0.8m, and the water was generally clear to the bottom when there was no wind. Except for total nitrogen (TN), the overall water quality met the Class IV surface water standard, and no submerged plants were observed. Several 1m×1m permeable enclosures were further subdivided within the enclosure. Seeds of different treatments of *Vallisneria natans*, *Hydrilla verticillata*, and *Myriophyllum spicatum* were evenly scattered into these enclosures for introduction. Seed treatments included uncoated seeds, primary pelleted seeds, and secondary pelleted seeds. Each treatment was implemented in triplicate, using a total of 27 1m×1m enclosures. The sowing density of the secondary pelleted seeds was 80 seeds / m². 2 The sowing density for primary pelleted seeds and uncoated seeds is 1200m. 2 (Myriophyllum spicatum is 1600m) 2 ).

[0035] On the day of seed release, observations revealed that a large number of uncoated seeds floated on the water surface. They gradually sank on the second day as they absorbed water and gained weight, but the settling speed was slow. During this period, they were easily concentrated on the surrounding silk netting due to water flow and waves. Seeds treated with pelleting all sank to the bottom. Secondary pelleted seeds sank significantly faster than primary pelleted seeds, and their overall structure remained largely intact upon reaching the bottom. However, seeds that underwent only primary pelleting showed a near-complete decomposition of their pelleted structure after settling.

[0036] Approximately 10 days after seed sowing, observable seedlings emerged from the submerged plant seeds in each enclosure. The number of germinating seedlings in the secondary and primary seedling groups was significantly higher than that in the unencapsulated group. Around 15 days later, the seed pellet structure in the secondary seedling group began to decompose. Table 2 shows the growth of submerged plants under different treatments two months after sowing. The unencapsulated group showed a scattered distribution of germinating submerged plants with poor uniformity; while the secondary seedling treatment group exhibited significantly better coverage and uniformity than the primary seedling group and the unencapsulated group.

[0037] Table 2. Growth (coverage) of submerged plants within the enclosure under different seed treatments.

[0038]

[0039] Example 2: Similar to Example 1, except that the bottom mud produced by bucket dredging is dehydrated by sun-drying and tilling. After about 4-5 days, the moisture content of the bottom mud decreases by about 35%. Calcium peroxide is applied to the surface of the bottom mud at a dosage of 4g / kg, and the agent is thoroughly mixed with the bottom mud by tilling.

[0040] The seed filler was prepared by uniformly mixing fine-grained soil and inorganic mineral filler at a weight ratio of 55:45. The selected submerged plant seed was *Potamogeton mongolicum*, and the seed growth medium contained medium-grained soil, fly ash, biomass, and microbial conditioner in a weight ratio of 55:25:10:0.1. During granulation, the chitosan solution used for atomized spraying was 1.5% concentrated, and the spraying amount was 2% of the mass of seed filler / seed growth medium / coarse-grained soil. The weight ratio of *Potamogeton mongolicum* seeds to seed filler was 1:8, resulting in primary pelleted seeds with a particle size of approximately 0.6 cm. For secondary granulation, 10 primary pelleted seeds were taken, and the weight ratio of primary pelleted seeds, seed growth medium, and coarse-grained soil was 1:60:20, resulting in secondary pelleted seeds with a particle size of approximately 8 cm. The site used was still the waters of the eastern part of a lake in Hubei Province as described in Example 1. In April, in a deep water area of ​​about 2m in depth, areas without submerged plants were selected and three 1m×1m experimental enclosures were built using permeable silk netting. These enclosures were used to sow the secondary pelleted seeds of Potamogeton crispus (80 seeds / m²). 2 By early September of the same year, the Potamogeton crispus in all three enclosures was growing well, with coverage rates reaching 75%, 65%, and 70%, respectively.

[0041] Example 3: A method for propagating submerged plant seeds based on bottom sediment reuse was implemented in a lake in Nanjing City. The average water depth was 1.8-2.5m, with poor hydrodynamic conditions. Some areas had severe bottom sediment accumulation, with a depth of 30-70cm. The surface sediment had extremely high water content and an organic matter content of 7.67%-10.92%, indicating severe eutrophication. Submerged plants were almost extinct, and there were signs of blue-green algal blooms. In April 2023, a cutter suction dredger was used for dredging. The resulting slurry was treated with PAC flocculation and then dewatered and solidified using a belt filter press. The solidified mud blocks had a water content of 45.7%. Calcium hypochlorite powder was applied to the surface of the solidified mud blocks at a dosage of 5g / kg, and the agent was thoroughly mixed with the bottom sediment by tilling. After the bottom sediment was completely air-dried, it was crushed and compacted. The rest of the preparation process is roughly the same as in Example 1. The difference is that fine soil and inorganic mineral filler are uniformly mixed at a weight ratio of 65:35 to obtain seed filler, and medium soil, fly ash, biomass and microbial conditioner are uniformly mixed at a weight ratio of 50:15:20:0.5 to obtain seed growth substrate.

[0042] The seeds of Vallisneria natans, Elodea nigra, and Potamogeton mongolicum were granulated using a granulator. The granulation process was largely the same as in Example 1, except that the chitosan solution concentration was 1%, and the amounts of chitosan solution used were 1%, 1%, and 2% of the mass of seed filler / seed growth substrate / coarse soil, respectively. Submerged plant seeds and seed filler were mixed and granulated at a weight ratio of 1:7 to obtain primary pelleted seeds with a particle size of 0.5 cm. For secondary granulation, 15, 15, and 20 primary pelleted seeds of Vallisneria natans, Elodea nigra, and Potamogeton mongolicum, respectively, were mixed with seed growth substrate and coarse soil at a weight ratio of 1:55:15 to produce secondary pelleted seeds with a particle size of approximately 5 cm.

[0043] After preparation, the secondary seeds of Vallisneria natans, Hydrilla verticillata, and Potamogeton mongolicum were evenly sown in an area of ​​200m² at the end of April 2023. 2 This is the initial experimental zone. Dredging has been completed within the experimental zone, and it has been separated from the external lake area by an impermeable enclosure. The experimental zone includes approximately 150 meters of shallow water (1.5-2 meters deep). 2 Sprinkle 75m each of Vallisneria natans and Hydrilla verticillata. 2 The spreading density is 80 grains / m² 2 ; 2-2.5m deep water area, approximately 50m 2 The main application method is to scatter *Potamogeton crispus* at a density of 60 seeds / m². 2 By mid-May, seed germination and seedling growth of various submerged plants could be observed. As temperatures rose, the submerged plants grew vigorously, and by the end of June, the coverage of Vallisneria natans, Hydrilla verticillata, and Potamogeton crispus in the experimental area was 70%, 65%, and 55%, respectively.

[0044] Example 4: It is largely the same as Example 1, except that the oxidant used is calcium nitrate, the submerged plant seeds are Elodea nuttallii, and the seed growth substrate is obtained by uniformly mixing medium-grained soil, fly ash, biomass and microbial conditioner in a weight ratio of 60:30:15:0.4. The particle size of the primary pelleted seeds is 0.4 cm.

[0045] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for propagating submerged plant seeds based on sediment recycling, characterized in that, Includes the following steps: S1. Dehydrate and solidify the bottom mud generated from dredging, add oxidant and mix, air dry, and then crush and remove impurities. S2. The sediment obtained in step S1 is sieved and classified into coarse soil (2-5mm), medium soil (0.05-2mm), and fine soil (less than 0.05mm) according to the sediment particle size. The fine soil is uniformly mixed with inorganic mineral filler to obtain seed filler, and the medium soil, fly ash, biomass and microbial conditioner are uniformly mixed to obtain seed growth substrate. S3. The submerged plant seeds are mixed with seed filler and granulated to produce primary pelleted seeds. The submerged plant seeds include seeds of Vallisneria natans, Myriophyllum spicatum, Elodea molluscina, Elodea nuttallii, and Potamogeton mongolicum. They are mixed with seed filler at a weight ratio of 1:6-8 and granulated separately to produce various primary pelleted seeds. During the mixing and granulation of the submerged plant seeds and seed filler, a chitosan solution with a concentration of 0.5-1.5% is sprayed evenly by atomization to ensure that the seed filler tightly coats the surface of the submerged plant seeds. The spraying amount is 1-2% of the mass of the chitosan solution to the seed filler. S4. The primary pelleted seeds are mixed with seed growth substrate and coarse soil for secondary granulation to produce secondary pelleted seeds. S5. The secondary pelleted seeds after secondary granulation are scattered in the target remediation water area to restore the submerged plant community.

2. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, The dewatering and solidification method in step S1 is determined according to the dredging method: the bottom mud generated by bucket dredging is dewatered by sun drying and tilling; the bottom mud generated by cutter suction dredging is dewatered and solidified by belt filter press, and the moisture content of the solidified bottom mud is controlled between 35% and 50%.

3. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, The oxidant in step S1 includes calcium hypochlorite, calcium nitrate, or calcium peroxide, and the application rate of the oxidant is 2.5-5 g / kg of the bottom sediment.

4. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, The inorganic mineral filler in step S2 includes vermiculite, fly ash, and sepiolite that have been physically crushed and passed through a 200-mesh sieve, with a mixing weight ratio of 1:1:1; fine-grained soil and inorganic mineral filler are uniformly mixed in a weight ratio of 55-65:35-45 to obtain a seed filler.

5. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, The fly ash mentioned in step S2 is obtained by crushing and passing it through a 2mm sieve; the biomass is obtained by drying and crushing reed stalks and then passing them through a 2mm sieve; the microbial conditioner includes Bacillus subtilis, Bacillus mucilaginosus, Nocardia fibrosis, Lactobacillus plantarum, and Thiobacillus denitrification, mixed in equal parts by weight; medium-grained soil, fly ash, biomass, and microbial conditioner are uniformly mixed in parts by weight of 50-60:20-30:10-20:0.1-0.5 to obtain a seed growth medium.

6. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, In step S4, the primary pelleted seeds, seed growth substrate, and coarse soil are mixed and granulated a second time at a weight ratio of 1:50-60:10-20.

7. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, The primary pelleted seeds in step S3 have a particle size of 0.3-0.6 cm, and the secondary pelleted seeds in step S4 have a particle size of 4-8 cm.

8. The method for propagating submerged plant seeds based on sediment recycling according to claim 1, characterized in that, Step S4, secondary mixing and granulation, uses 10-20 primary pelleted seeds. During the mixing and granulation of the primary pelleted seeds and seed growth medium, a chitosan solution with a concentration of 0.5-1.5% is sprayed by atomization, and the amount of chitosan solution is 1-2% of the mass of the seed growth medium. Then, coarse soil is added and mixed and granulated. During the mixing and granulation, a chitosan solution with a concentration of 0.5-1.5% is sprayed by atomization, and the amount of chitosan solution is 1-2% of the mass of the coarse soil, to obtain secondary pelleted seeds.

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