Methods for promoting the growth of aquatic plants and seaweed bed substrates

Abstract

This invention provides a growth promotion method that is highly effective in promoting the growth of aquatic plants. [Solution] A method for promoting the growth of aquatic plants, comprising the step of placing a seaweed bed base, which includes a porous body formed from a composition containing a base component, a water-soluble nitrate compound, and a water-soluble phosphate compound, in water.

Description

[Technical Field]

[0001] This invention relates to a method for promoting the growth of aquatic plants and to a substrate for seaweed beds. [Background technology]

[0002] As part of climate change countermeasures, initiatives that contribute to carbon sequestration are attracting attention. Atmospheric CO2 dissolved in the ocean is taken up by photosynthesis in aquatic plants such as seaweed, and is sequestered and stored as organic matter. Furthermore, when aquatic plants die and decompose, carbon is continuously sequestered and stored as it remains in the deep mesopelagic layer. Therefore, the active creation of seaweed beds is desired as an option for carbon sequestration.

[0003] Patent Document 1 proposes an underwater environment restoration structure made of concrete blocks mixed with a predetermined amount of algae growth-inducing substance selected from amino acids and nucleic acids. This underwater environment restoration structure is said to be able to restore seaweed beds over a wide area by releasing an appropriate amount of algae growth-inducing substance over a long period of time, thereby preventing the dominance of jointless coralweed colonies in areas suffering from coastal barrenness. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-191892 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the above-mentioned underwater environment restoration structure is insufficient in promoting the growth of aquatic plants. Therefore, the present invention aims to provide a growth promotion method and a seaweed bed substrate that are excellent in promoting the growth of aquatic plants. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A method for promoting the growth of aquatic plants, comprising the step of placing a seaweed bed base, which includes a porous body formed from a composition comprising a base component, a water-soluble nitrate compound, and a water-soluble phosphate compound, in water. [2] The content of the water-soluble nitrate compound is 1 to 30 kg / m³ in terms of the mass of nitrate nitrogen per volume of the porous body. 3 The method for promoting the growth of aquatic plants as described in [1] above. [3] The content of the water-soluble phosphorus compound is 1 to 30 kg / m³ in terms of the mass of phosphorus per volume of the porous body. 3 The method for promoting the growth of aquatic plants as described in [1] or [2] above. [4] A method for promoting the growth of aquatic plants according to any one of [1] to [3], wherein the base component comprises cement and water. [5] Before the step of placing the seaweed bed base in water, A method for promoting the growth of aquatic plants according to [4], comprising the step of performing a carbonation treatment on the porous body. [6] The method for promoting the growth of aquatic plants according to [5], wherein the carbonation treatment is a treatment in which the porous body is held in an atmosphere containing carbon dioxide at a higher concentration than that in the air. [7] The porous body is granular with a particle size of 10 cm or less, A method for promoting the growth of aquatic plants according to any one of [1] to [6], wherein the seaweed bed base includes a plurality of the porous bodies. [8] A seaweed bed substrate comprising a porous body formed from a composition comprising a base component, a water-soluble nitrate compound and a water-soluble phosphate compound. [9] The content of the water-soluble nitrate compound is 1 to 30 kg / m³ in terms of the mass of nitrate nitrogen per volume of the porous body. 3 The seaweed bed substrate described in [8] above.

[10] The content of the water-soluble phosphorus compound is 1 to 30 kg / m³ in terms of the mass of phosphorus per volume of the porous body. 3 The seaweed bed substrate described in [8] or [9] above.

[11] The seaweed bed substrate according to any one of [8] to

[10] , wherein the base components include cement and water.

[12] The porous body is granular with a particle size within 10 cm, The algal bed substrate according to any one of [8] to

[11] , wherein the algal bed substrate includes a plurality of the porous bodies.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a growth promotion method and an algal bed substrate that are excellent in the effect of promoting the growth of aquatic plants.

Brief Description of the Drawings

[0008] [Figure 1] It is a graph showing the results of Test Example 1. [Figure 2] It is a graph showing the results of Test Example 2. [Figure 3] It is a photograph showing the results of Test Example 3.

Modes for Carrying Out the Invention

[0009] In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value. Hereinafter, embodiments of the present invention will be described.

[0010] The method for promoting the growth of aquatic plants of the present invention includes the step of disposing the algal bed substrate of the present invention in water. The algal bed substrate of the present invention includes a porous body formed from a composition containing a base component, a water-soluble nitrate compound, and a water-soluble phosphate compound (hereinafter, also referred to as a composition for forming a porous body). The composition for forming a porous body will be described in detail later.

[0011] When the algal bed substrate containing the porous body of the present invention is disposed in water, seeds or spores of aquatic plants adhere to the porous body, providing a foothold for the growth of aquatic plants. Further, the water-soluble nitrate compound and the water-soluble phosphate compound gradually elute into the water from the porous body. In the growth of aquatic plants, nitrogen and phosphorus are regarded as necessary nutrients. Water-soluble nitrate compounds and water-soluble phosphate compounds are nitrogen sources and phosphorus sources respectively, and the gradual elution of these promotes the growth of aquatic plants. Generally, plants absorb nitrogen in a state that has undergone nitrification from ammonia nitrogen and nitrite nitrogen to nitrate nitrogen. When nitrogen is supplied in the nitrate state, an excellent growth promotion effect is expected. Both nitrogen and phosphorus are components that contribute to the growth of stems, leaves and roots, but the nitrogen absorption efficiency increases in the presence of phosphorus. The supply of both water-soluble nitrate compounds and water-soluble phosphate compounds is expected to have a synergistic effect on the growth promotion of aquatic plants.

[0012] Examples of the shape of the porous body include granular, wave-dissipating block shape, and porous concrete. The granular porous body may be in the shape of a polyhedron such as a cube, spherical, irregular shape (for example, a crushed porous body), etc.

[0013] The porosity of the porous body is preferably 5 to 40%, more preferably 10 to 20%. When the porosity is not less than the above lower limit value, the elution properties of the water-soluble nitrate compound and the water-soluble phosphate compound are more excellent. When the porosity is not more than the above upper limit value, the strength of the porous body is more excellent. The porosity is measured, for example, by dividing the difference between the mass when immersed in water for 24 hours or more and the mass when naturally dried for 72 hours or more by the volume of the porous body.

[0014] The number of porous bodies contained in the algal bed substrate may be one or a plurality, and can be appropriately set according to the size of the porous body and the size of the algal bed substrate. When the size of the entire algal bed substrate is the same, the elution properties of the water-soluble nitrate compound and the water-soluble phosphate compound tend to be more excellent when the number of porous bodies constituting the algal bed substrate is larger. Therefore, it is preferable that the algal bed substrate contains a plurality of porous bodies.

[0015] The seaweed bed base may consist solely of porous material, or it may be a combination of porous material and other materials. Examples of other materials include fibrous material, wood, and rock.

[0016] The location where the seaweed bed substrate is placed can be anywhere where aquatic plants can grow, and it can be in saltwater or freshwater. Examples include the seabed, coast, lakebed, lakeshore, riverbed, and riverbank. The aquatic plants that can be grown are not particularly limited. Examples include *Sargassum fusiforme*, *Wakame seaweed*, *Kelp*, *Zostera marina*, *Gelidium palmatum*, *Nori*, *Ulva lactuca*, *Mozuku seaweed*, *Ceratophyllum demersum*, and *Sargassum humilis*.

[0017] The method of placing the seaweed bed substrate underwater is not particularly limited. Examples include scattering multiple granular porous materials at a predetermined location, placing multiple granular porous materials in a mesh bag at a predetermined location, and installing wave-dissipating block-shaped porous materials at a designated location. The seaweed bed base may also serve as a foundation material for structures installed on the seabed or other surfaces. Examples of such structures include wind turbines for wind power generation, piers, breakwaters, and wharves.

[0018] After placing the seaweed bed substrate in the water, it may be left as is, or it may be retrieved after a certain period of time. At least, it is preferable to leave the seaweed bed substrate in the water for the period from when the seeds or spores of the target aquatic plants are established until they reach maturity. Taking the algae species *Sargassum fuscipes* as an example, the period from establishment to maturity is approximately 6 months, so it is preferable to leave the seaweed bed substrate in the water for at least 6 months.

[0019] <Composition for forming porous body> Examples of base components include hydraulic compositions and porous silica. The hydraulic composition contains a hydraulic binder and water. The hydraulic binder is a powder that hardens upon reaction (hydration reaction) with water, and examples include cement, gypsum, and hydraulic lime. As a base component, a hydraulic composition containing cement and water (hereinafter also referred to as a cement composition) is preferred due to the simplicity of the manufacturing process for the porous body.

[0020] Cement is not particularly limited as long as it is a powder that hardens through a chemical reaction with water, with limestone, clay, silica, iron oxide, etc. as the main raw materials. Examples include Portland cement (JIS R 5210:2009), blast furnace cement (JIS R 5211:2009), silica cement (JIS R 5212:2009), fly ash cement (JIS R 5213:2009), and eco-cement (JIS R 5214:2009).

[0021] Portland cement is standardized into 12 types: six types of Portland cement—ordinary, rapid-hardening, very rapid-hardening, moderate-heat, low-heat, and sulfate-resistant—and their respective low-alkali variations (JIS R 5210:2009).

[0022] Blast furnace cement is classified into three types—Type A, Type B, and Type C—depending on the amount of blast furnace slag mixed in (JIS R 5211:2009). Blast furnace cement type A... Blast furnace slag content: 5-30% by mass Blast furnace cement type B... Blast furnace slag content: 10-60% by mass Blast furnace cement type C... Blast furnace slag content: 60-70% by mass

[0023] The water used is not particularly limited, and water conforming to JIS A 5308:2019 "Ready-Mixed Concrete" can be used. In the cement composition, the water-cement ratio (W / C), which is the mass percentage of water to cement, is preferably 40-100%, and more preferably 50-70%.

[0024] The cement composition may further contain other components besides cement and water. Examples of other components include aggregates, chemical admixtures, and other admixtures. It is preferable to include aggregate because it increases the porosity of the formed porous body, making it easier for water-soluble nitrate compounds and water-soluble phosphate compounds to leach out.

[0025] Examples of aggregates include fine aggregate and coarse aggregate, and these may be used in combination. The fine aggregate is not particularly limited and can be any fine aggregate for concrete as specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete," etc. The coarse aggregate is not particularly limited and can be any coarse aggregate for concrete as specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete," etc.

[0026] The chemical admixture is not particularly limited, and any chemical admixture that is normally used in combination with cement can be used.

[0027] For water-soluble nitrate compounds and water-soluble phosphate compounds, "water solubility" simply means that they can be eluted into water from a porous material. Examples of water-soluble nitrate compounds include water-soluble nitrates such as calcium nitrate, ammonium nitrate, sodium nitrate, and potassium nitrate, as well as nitric acid. Two or more of these may be used in combination. Examples of water-soluble phosphate compounds include water-soluble phosphates such as ammonium phosphate, sodium phosphate, and potassium phosphate, as well as phosphoric acid. Two or more of these may be used in combination.

[0028] The amount of water-soluble nitrate compounds and water-soluble phosphate compounds in the porous body-forming composition is preferably such that the elution of water-soluble nitrate compounds and water-soluble phosphate compounds continues from the establishment of aquatic plant seeds and spores on the seaweed bed substrate to the maturation period of the aquatic plants. Taking the algae *Sargassum erythrosora* as an example, the period required from establishment to maturation is approximately 6 months. Therefore, it is preferable that the elution of water-soluble nitrate compounds and water-soluble phosphate compounds continues for at least 6 months.

[0029] In the composition for forming a porous body, the content of the water-soluble nitrate compound is 1 to 30 kg / m in terms of the mass of nitrate nitrogen per volume of the porous body formed from the composition for forming a porous body. 3 is preferable, and 5 to 30 kg / m 3 is more preferable, and 10 to 30 kg / m 3 is even more preferable. When the content of the water-soluble nitrate compound is at least the lower limit value, the period during which the elution of the water-soluble nitrate compound persists becomes sufficiently long. When the content of the water-soluble nitrate compound is at most the upper limit value, the cost required for production can be reduced. Further, when the base component is a cement composition, when the content of the water-soluble nitrate compound is at most the upper limit value, rapid curing of the composition for forming a porous body during the preparation of the composition for forming a porous body can be suppressed.

[0030] In the composition for forming a porous body, the content of the water-soluble phosphate compound is 1 to 30 kg / m in terms of the mass of phosphorus per volume of the porous body formed from the composition for forming a porous body. 3 is preferable, and 10 to 30 kg / m 3 is more preferable. When the content of the water-soluble phosphate compound is at least the lower limit value, the period during which the elution of the water-soluble phosphate compound persists becomes sufficiently long. When the content of the water-soluble phosphate compound is at most the upper limit value, the cost required for production can be reduced.

[0031] The composition for forming a porous body may further contain other components other than the base component, the water-soluble nitrate compound, and the water-soluble phosphate compound, as long as the effects of the present invention are not significantly impaired as necessary. Examples of the other components include silicon and the like.

[0032] The composition for forming a porous body can be prepared by mixing the base component, the water-soluble nitrate compound, the water-soluble phosphate compound, and other components as necessary. If the base component is a cement composition, the cement composition may be prepared by kneading each component of the cement composition, and then kneading in a water-soluble nitrate compound and a water-soluble phosphate compound to prepare a porous body forming composition. Alternatively, the porous body forming composition may be prepared by kneading in each component of the cement composition, a water-soluble nitrate compound, and a water-soluble phosphate compound.

[0033] <Method for forming porous materials> Methods for forming a porous body from a porous body-forming composition can be known, depending on the base component. For example, if the base component is a cement composition, the porous body forming composition is molded by pouring it into a formwork, and then cured to harden. The hardened body obtained in this way may be used as is as a porous body, or it may be further processed by crushing, cutting, or other methods. The method of treatment is not particularly limited and can be appropriately selected from known treatment methods such as airborne treatment, sealing treatment, and poultice treatment. There are no specific limitations on the curing period, and it can be selected as appropriate depending on the curing method. For example, in the case of sealing or poultice curing, about 7 days is preferable.

[0034] <Carbonation treatment> If the base component is a cement composition, it is preferable to perform a carbonation treatment on the porous body before placing the seaweed bed base in water. When the base component is a cement composition, the porous body formed from the porous body-forming composition is generally strongly alkaline with a pH of around 12-13. If such a porous body is placed directly in water, the water surrounding the porous body will become alkaline, which may slow down the decomposition and elution rates of water-soluble nitrate compounds and water-soluble phosphate compounds. By pre-treating the porous body with carbonation to lower its pH, a sufficient amount of water-soluble nitrate compounds and water-soluble phosphate compounds can be continuously eluted.

[0035] Examples of carbonation treatments include the following methods. Among these, Method 1 is preferred in terms of carbonation rate and the effect of preventing the elution of water-soluble nitrate compounds and water-soluble phosphate compounds. Method 1: A process of holding a porous material in an atmosphere containing carbon dioxide (hereinafter also referred to as CO2) at a higher concentration than that of the atmosphere (hereinafter also referred to as a CO2 atmosphere). Method 2: A process in which the surface of a porous material is repeatedly dried by allowing it to absorb water through watering, etc., and then bringing it into contact with the air using a blower or the like. Method 3: A porous material is immersed in an aqueous solution with high CO2 solubility, and CO2 is bubbled into the aqueous solution.

[0036] In Method 1, the CO2 atmosphere may consist solely of CO2, or it may further contain other gases besides CO2. The CO2 concentration in the CO2 atmosphere is preferably 5% or higher. The time for holding a porous material under a CO2 atmosphere is, for example, 24 to 500 hours.

[0037] The pH of the porous material after carbonation treatment is preferably 7 to 10. The pH of a porous material can be easily measured by placing pH test paper in contact with the porous material and spraying it with water.

[0038] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments and can be freely modified within the scope of the present invention. [Examples]

[0039] Examples of the present invention are shown below, but these examples are for illustrative purposes only and do not limit the content of the present invention.

[0040] <Test Example 1> (1) Fabrication of porous material Concrete was prepared by mixing cement (C), water (W), fine aggregate (S), coarse aggregate (G), chemical admixture (SP), and calcium nitrate (N) according to the proportions shown in Table 1. The resulting concrete was poured into a formwork (100 × 100 × 400 mm) and cured to harden. The resulting prismatic hardened body was removed from the formwork and cut in the short-side direction to a thickness of 20 mm. The water-cement ratio (W / C) was 40% or 60%. The amount of calcium nitrate (N) was calculated as 20 kg / m³ in terms of the mass of nitrate nitrogen per unit volume of porous material. 3 The amount was determined to be [amount]. Curing was carried out for 7 days using moist curing. Control represents an example without added nutrients (N), N40 represents an example with a W / C ratio of 40%, and N60 represents an example with a W / C ratio of 60%.

[0041] [Table 1]

[0042] (2) Dissolution test The prepared porous material was immersed in a container filled with tap water. During this process, fresh tap water was continuously supplied to the container, ensuring that the water circulated within the container. After the specified number of days had elapsed, the porous material was removed from the container. The concentration was 5 mL / cm² relative to the exposed surface area of ​​the porous material. 2 A corresponding amount of distilled water was newly measured, and the porous material was immersed in this distilled water. After 24 hours had passed since immersion, the water in which the porous material was immersed (immersion water) was stirred, and the amount of nitrate ion elution was used as a sample. The nitrate ion concentration of the obtained samples was measured using the JIS K 0102 flow analysis method, and the amount of nitrogen eluted per liter of distilled water was determined.

[0043] (3) Results The results of the dissolution test are shown in Figure 1. In the case without added nutrients, the results consistently showed levels below the detection limit. On the other hand, under both the 40% and 60% W / C conditions, it was confirmed that nitrogen levels of 2 mg / L or more were continuously leaching from the porous material even after 56 days. Furthermore, in this study, the nitrogen elution amount on the 7th day from the start of the elution test was 22 mg / L for W / C 60% and 18 mg / L for W / C 40%, indicating a tendency for higher initial nitrogen elution to occur with higher W / C ratios.

[0044] <Test Example 2> (1) Fabrication of porous material Concrete 1 was prepared by mixing cement (C), water (W), fine aggregate (S), coarse aggregate (G), and chemical admixture (SP). Concrete 2 was prepared by mixing cement (C), water (W), fine aggregate (S), coarse aggregate (G), chemical admixture (SP), calcium nitrate (N), and ammonium hydrogen phosphate (P). The mix designs for Concrete 1 and Concrete 2 are shown in Table 2. The obtained concretes 1 and 2 were poured into formwork (100 x 100 x 400 mm) and cured to harden. The resulting prismatic hardened bodies were removed from the formwork and cut along the shorter side to a thickness of 20 mm, obtaining porous body 1 from concrete 1 and porous body 2 from concrete 2. In both cases, the W / C ratio was 60%. The amount of calcium nitrate (N) added was 20 kg / m³, calculated as the mass of nitrate nitrogen per volume of the porous body. 3 The amount was set to be such that the amount of phosphorus per unit volume of porous material is 15 kg / m³. 3 The amount was determined to be [amount]. Curing was carried out for 7 days using moist curing.

[0045] [Table 2]

[0046] (2) Carbonation treatment The prepared porous material was subjected to a carbonation treatment by standing it in a CO2 atmosphere with a CO2 concentration of 5% (100 times that of air) for 336 hours.

[0047] (3) Dissolution test A porous material that had undergone carbonation treatment was immersed in a container filled with artificial seawater. During this process, fresh seawater was continuously supplied to the container, ensuring that the seawater circulated within the container. After the specified number of days had elapsed, the porous material was removed from the container. The concentration was 5 mL / cm² relative to the exposed surface area of ​​the porous material. 2 A corresponding amount of distilled water was newly measured, and the porous material was immersed in this distilled water. After 24 hours had passed since immersion, the water in which the porous material was immersed (immersion water) was stirred, and the amount of nitrate ion elution was used as a sample. The nitrate ion concentration of the obtained samples was measured using the JIS K 0102 flow analysis method, and the amount of nitrogen eluted per liter of distilled water was determined.

[0048] (4) Cultivation of wakame seaweed The growth of wakame seaweed was evaluated using a porous material treated with carbonation. Commercial seedling ropes with wakame sprouts attached were mounted on the carbonation-treated porous material and immersed in artificial seawater for growth evaluation. To recreate a nutrient-poor ocean environment, commercially available artificial seawater for low-nutrient environments was used.

[0049] (4) Results In the dissolution test, sustained dissolution of nitrogen exceeding 2 mg / L was confirmed for at least six months. In wakame cultivation, as shown in Figure 2, it was observed that growth deterioration was suppressed and delayed under conditions in which a carbonated porous material was immersed in artificial seawater.

[0050] <Test Example 3> (1) Fabrication of porous material Concrete 1 and Concrete 2, prepared according to the mix designs of Concrete 1 and Concrete 2 in Test Example 2, were poured into formwork (250 mm in diameter x 50 mm in height) and cured to harden. In both cases, the W / C ratio was 60%. The resulting disc-shaped hardened body was removed from the formwork, fixing bolts were installed, and porous body 1 was obtained from concrete 1, and porous body 2 from concrete 2.

[0051] (2) Carbonation treatment The prepared porous material was subjected to a carbonation treatment by standing it for 72 hours in a CO2 atmosphere at 20°C and 60% RH with a CO2 concentration of 5% (100 times that of air).

[0052] (3) Evaluation of the promotion of seaweed bed formation in the sea The fabricated porous material was installed at a depth of approximately 10m off the coast of Nyuzen, Toyama Prefecture. The effect of promoting seaweed bed formation was evaluated based on the appearance of the porous material one month and eleven months after installation.

[0053] (4) Results Figure 3 shows the appearance of porous body 1 and porous body 2 at the time of installation, one month after installation, and eleven months after installation. At one month after installation, it was confirmed that porous body 2 had more brown deposits than porous body 1. Furthermore, at eleven months after installation, porous body 2 had a much larger amount of algae growth than porous body 1.

Claims

1. A method for promoting the growth of aquatic plants, comprising the step of placing a seaweed bed base, which includes a porous body formed from a composition containing a base component, a water-soluble nitrate compound, and a water-soluble phosphate compound, in water.

2. The content of the water-soluble nitrate compound is 1 to 30 kg / m³ in terms of the mass of nitrate nitrogen per unit volume of the porous body. ３ The method for promoting the growth of aquatic plants according to claim 1.

3. The content of the water-soluble phosphorus compound is 1 to 30 kg / m³ in terms of the mass of phosphorus per volume of the porous body. ３ The method for promoting the growth of aquatic plants according to claim 1 or 2.

4. The method for promoting the growth of aquatic plants according to claim 1 or 2, wherein the base component comprises cement and water.

5. Before the step of placing the aforementioned seaweed bed base underwater, The method for promoting the growth of aquatic plants according to claim 4, further comprising the step of performing a carbonation treatment on the porous body.

6. The method for promoting the growth of aquatic plants according to claim 5, wherein the carbonation treatment is a treatment in which the porous body is held in an atmosphere containing carbon dioxide at a higher concentration than that in the air.

7. A seaweed bed substrate comprising a porous body formed from a composition containing a base component, a water-soluble nitrate compound, and a water-soluble phosphate compound.

8. The content of the water-soluble nitrate compound is 1 to 30 kg / m³ in terms of the mass of nitrate nitrogen per unit volume of the porous body. ３ The seaweed bed substrate according to claim 7.

9. The content of the water-soluble phosphorus compound is 1 to 30 kg / m³ in terms of the mass of phosphorus per volume of the porous body. ３ The seaweed bed substrate according to claim 7 or 8.

10. The seaweed bed substrate according to claim 7 or 8, wherein the base components include cement and water.

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