JP2018183080A - Modified soil for creating brackish water eelgrass bed, and method for creating brackish water eelgrass bed using the same, and method for growing eelgrass in brackish water region - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modified soil for creating an eelgrass bed which can suppress solidification of a seaweed bed and a rise of soil PH as much as possible even when used in a brackish water region and create the eelgrass bed suitable for raising the eelgrass, a method for creating a brackish water eelgrass bed using the same, and a method for growing the eelgrass.SOLUTION: A modified soil for creating a brackish water eelgrass bed used in a brackish water region is made of a mixture of dredged sediment and fine-particles removal steel slag in which fine-particles in the steel slag are removed. A method for creating a brackish water eelgrass bed is given in which the fine-particles removal steel slag obtained by removing fine-particles in the steel slag is mixed into the dredged sediment to prepare the modified soil, and the modified soil is laid on the bottom material of the brackish water region to create the eelgrass bed. A method for growing the eelgrass in the brackish water region is given using the modified soil.SELECTED DRAWING: None

Description

  The present invention relates to a modified soil for creating an ammo field used in brackish water where seawater and fresh water are mixed in a water area near the mouth of a river, a deeply penetrated inner bay water area, a water area from land on a tidal flat, and the like. The present invention relates to a method for building a eelgrass field in a brackish water area and a method for growing eelgrass in a brackish water area.

  As plants grown in the sea, there are seagrasses such as eelgrass that grow by seeds, grow roots in sandy or sandy mud, and ingest nutrients from these roots, just like land plants. The area where seaweeds gather is called the seagrass bed. Although 16 species of seaweeds have been confirmed in the country, it is generally called an amamo field because it is the ammo that forms the community. And when this Amamo field is formed on the coastline between the land and the sea, biodiversity is brought about, and diatoms and zooplankton adhere to the leaves and become spawning grounds and feeding grounds for seafood. In addition to the formation of a rich ecosystem, it will also function as a water purification.

  However, in recent years, sea sand has been washed away due to land reclamation and concrete conversion in the gulf area, and sludge has become sludge due to factory effluent, etc. The movement to improve the environment has started, and along with this, attempts have been made to create and restore eelgrass fields.

  And when building an ammo ground in such a bay area, a large amount of construction material is required to be laid in the construction area. It is ideal to use natural stone, natural sand (sea sand or mountain sand), but it is often difficult due to factors such as the depth of the construction site and the environment. There is also a risk of introducing new environmental problems.

Therefore, the utilization of recycled materials as construction materials is being considered for the construction of amamo fields, but the use of steel slag produced as a by-product in the steel making process has also been proposed as a material that can be procured in large quantities and at low cost.
For example, in Patent Document 1, in order to solve the problems of the elution of sulfur from slag particles generated in the initial stage of deposition and the increase in pH of surrounding water, the surface of the slag particles is carbonated and the surface of the slag particles is preliminarily calcium carbonate. It has been proposed to use blast furnace pyroclastic slag coated with a coating as an amamo field construction material.

  Moreover, in patent document 2, the ratio of the slag lump with a particle size of 100 mm or more is 60 mass% or more, and the steelmaking slag whose ratio of the slag lump with a particle size of 30-300 mm is 95 mass% or more is constructed in a water bottom. It has been proposed to be used as a material for submerged dikes, and it is described that seaweeds adhere to steelmaking slag used as a material for submerged dikes. And in patent document 3, in order to ensure the elution ability of the mineral content from the inside of slag, and the fixing ability with respect to the hydrogen sulfide and phosphorus which melt | dissolved in the surrounding water, the carbonized steel without a carbonate film on the surface It has been proposed to use slag as part or all of the aquatic environment conservation material.

Further, in Patent Document 4, a blast furnace granulated slag or a mixture of a blast furnace granulated slag and another substrate material is laid and consolidated by the latent hydraulic action of the blast furnace granulated slag. By setting the particle size of the granulated slag to D ₂₀ = 0.15 to 1.2 mm and D ₅₀ = 0.6 to 1.9 mm, the substrate surface hardness measured with a Yamanaka type surface hardness tester (standard type) can be obtained. Artificial water-bottom substrates that have an average value of 3 to 20 mm and are suitable for the construction of seagrass beds such as eelgrass beds in shallow waters and tidal flats facing the coast have been proposed. Patent Document 5 proposes an artificial shallow field or tidal flat constructed using a mixed material of clay and steel slag having a free CaO content of 0.5 mass% or more as a filling material.

  In Patent Document 6, for example, a particle size distribution of 0.075 mm or less is 10% by mass or less, a particle size of 26.5 mm or more has a particle size distribution of 5% by mass or less, and 50% particle size A modified soil obtained by mixing steelmaking slag having a particle diameter of 50% or more and 15 mm or less in a dredged sand, the hardness measured by a Yamanaka hardness meter Using modified soil that reaches 20 kPa or more and 500 kPa or less on the 30th day after the mixing, and within the range of 20 kPa or more and 500 kPa or less after the 30th day after the mixing, the modified soil is laid on the seabed to form seaweeds A method to create a eelgrass field that nurtures the pupae has been proposed.

Japanese Patent Laid-Open No. 2004-236,546 JP 2005-256,497 JP 2005-320,230 JP 2006-288,323 A JP 2011-208,365 Japanese Patent No. 6,048,088

By the way, the present inventors prepared a modified soil by mixing dredged sand and steelmaking slag based on the method described in Patent Document 6, and using the resulting modified soil, A certain result has been obtained so far about the development of the field and the cultivation of the eelgrass in the eelgrass farm that has been created. Therefore, using the same modified soil as described in Patent Document 6 obtained by mixing dredged soil and steelmaking slag, an attempt was made to create an ammo field in brackish water. As a result, it was found that the soil pH would rise to such an extent that the modified soil was not favorable for the growth of sea cucumbers in brackish waters.
Here, the brackish water area in the present invention means a water area of 1.5 to 3% by mass, which is less than the salinity concentration of seawater in a broad sense, but in a narrow sense, which is a salinity concentration at which sea eels can grow.

  Therefore, as a result of further investigation on this cause, the present inventors have found that in brackish water, the salinity of brackish water is lower than that of seawater and its buffer capacity is weaker than that of seawater, and the salinity of brackish water is low. Correspondingly, it was found that the buffering capacity was lowered, and it was clarified that the pH value of the seaweed bed needs to be a weakly alkaline area of less than 9.0 for the growth of sea eels, and the sea bream field was created in the brackish water area. It was decided to study the development of modified soil suitable for this.

  And in order not to raise the pH in the newly built eelgrass field, the use of carbonated steelmaking slag in which the steelmaking slag was carbonized to form a carbonate film on the slag surface was also studied. In steelmaking slag, as described in Patent Document 3, the elution of mineral components from the inside of the slag to the outside is suppressed, and the ability to fix water sulfide and phosphorus in the surrounding area is impaired and the function as a water quality improvement is also suppressed. Furthermore, the use of “carbonated steelmaking slag whose surface is not coated with a carbonate film” proposed in Patent Document 3 is also relatively large in labor and cost. There is a problem that mass procurement is difficult.

  Under these circumstances, the present inventors can prepare easily and inexpensively and can be procured in large quantities, and also impair the functions of supplying mineral components and improving water quality of steelmaking slag. In addition, the following knowledge was obtained in the course of further study on the development of modified soil suitable for the construction of eelgrass fields in brackish waters. That is, when steelmaking slag is mixed with dredged soil, fine particles adsorb moisture in the sediment, and at the same time, solidification starts by the hydration reaction of free CaO on the slag surface and Si ions in the pore water. It was found out that the pH value of the pore water rose above pH 9.0. Further, by removing fine particles from steelmaking slag, specifically, by removing fine particles by classification treatment, fine particles having a large surface area are removed from steelmaking slag and / or by washing treatment. It was also found that the fine particles attached to the surface of the remaining steelmaking slag were removed, and the alkali elution reaction on the surface of the slag became gentle. And even when an ammo field is created in brackish water by using a modified soil prepared by mixing fine-particle-removed steelmaking slag from which fine-grain content has been removed and dredged soil, solidification of the soil is The present invention was completed by confirming that it was not expressed and that the increase in pH could be suppressed as much as possible.

Accordingly, an object of the present invention is to provide a eelgrass field that can suppress the solidification of the algae basin and increase in pH as much as possible even when used in brackish water, and can create an eelgrass field suitable for nurturing eel It is to provide improved soil for creation.
Another object of the present invention is to provide a method for creating an ammo field in a brackish water area using the above-mentioned modified soil for creating an ammo field.
Furthermore, another object of the present invention is to provide a method for creating an eelgrass field in a brackish water area using the above-mentioned modified soil for creating a eelgram field and cultivating eelgrass in the brackish water area.

  That is, the present invention is as follows.

(1) A modified soil for use in brackish water ammo fields for use in brackish water characterized by comprising a mixture of dredged sand and fine-grain-removed steel slag from which fine particles in steel slag have been removed.
(2) The modified soil for brackish water ammo field construction according to (1), wherein the fine-grain-removed steel slag is a steel slag from which fine-grained particles having a particle diameter of 2 mm or less have been removed.
(3) The modified soil for brackish water ammo field construction as described in (1) above, wherein the fine particle-removed steel slag is a steel slag from which fine particles having a particle diameter of 5 mm or less have been removed.
(4) The fine grain-removed steel slag is a steelmaking slag and / or a blast furnace slow-cooled slag from which fine grains in the steel-making slag and / or blast furnace slow-cooled slag have been removed (1) Modified soil for brackish water amamo field construction according to any one of to (3).
(5) The modified soil for brackish water ammo field construction according to any one of (1) to (4), wherein the modified soil has a pH value of less than 9.0.

(6) When laying modified soil on the bottom of brackish water area and creating an ammo ground in brackish water area,
Fine slag removed steel slag is prepared by removing fine particles in steel slag, and the modified soil obtained by mixing the prepared fine slag removed steel slag and dredged sand is prepared. A method for constructing a brackish amamo field, characterized by laying pelagic soil on the bottom sediment of the brackish water area to create an ammo field.
(7) Prior to laying the modified soil on the bottom of brackish water, embankment is performed on the bottom sediment, and the modified soil is laid on the embankment. How to create a water eel
(8) The method for constructing a brackish water ammo field according to (7), wherein the embankment is laid so that a water depth is 5 m or less.
(9) When preparing the fine-grain-removed steel slag, measure the brackish water salinity of the amamo field construction area in the brackish water area, and fine particles to be removed from the steel slag according to the brackish-water salinity The method for creating a brackish water ammo field according to any one of the above (6) to (8), wherein the diameter is determined, and fine particles having the determined particle diameter are removed from the steel slag.
(10) The particle size of the fine particles to be removed from the steel slag is based on a previously prepared calibration curve of salinity concentration-modified soil pH value, from the brackish water salinity concentration in the brackish water area to the pH of the modified soil. The method for constructing a brackish water ammo field according to the above (9), wherein the value is determined so as to be in a weak alkaline region of less than 9.0.
(11) The fine-grain-removed steel slag is prepared by classifying and / or washing the steel slag, and the brackish water ammo field according to any one of the above (6) to (10) Creation method.
(12) Any of the above (6) to (11), wherein seaweed seeds are mixed in advance in the modified soil, and the obtained modified soil containing seeds is laid on the bottom sediment of a brackish water area The construction method of the brackish water ammo ground described in 1.
(13) Place the modified soil in a breeding vessel that can be decomposed in brackish water, sow seeds of seaweeds on the modified soil, and distribute the modified soil sowed with seeds to the bottom sediment of the brackish water area together with the growing vessel. The method for constructing a brackish water ammo field according to any one of the above (6) to (12), characterized by comprising:
(14) The method for creating a brackish water eel field as described in (13) above, wherein the seaweed seeds are sown from the surface of the modified soil to a depth of 1 to 2 cm.
(15) Putting the modified soil in a breeding vessel capable of decomposing in brackish water, sowing seeds of seaweeds on the modified soil, and growing and germinating seedlings together with the modified soil and the growing vessel in the bottom sediment of the brackish water area The method for constructing a brackish water eel field as described in (13) or (14) above, wherein

  (16) A method for growing sea eels in brackish water characterized by nurturing sea eels and / or core sea breams using the sea bream field created by the construction method according to any one of (6) to (15) .

According to the modified soil for creating a brackish water ammo field of the present invention, it is possible to create an ammo field suitable for the growth of sea cucumber in the brackish water area by suppressing the solidification of the seaweed field and the increase in pH as much as possible. .
In addition, according to the method for creating a brackish water eel field of the present invention, it is possible to easily create an eel field suitable for nurturing eel in the brackish water region.
Furthermore, according to the method for growing sea bream in the brackish water area of the present invention, it is possible to easily grow sea bream in the brackish water area.

Fig. 1 uses steelmaking slag (0 to 25 mm) as steel slag, and removes fine particles removed from the steelmaking slag, salinity concentration of simulated brackish water prepared by diluting seawater, and fine particles. Fine grain content-salinity concentration-obtained when investigating the relationship with the pH value in the modified soil obtained by mixing the obtained fine grain-removed steelmaking slag into dredged soil at 20 vol% It is a graph of pH value. FIG. 2 is a graph showing the change in pH value from the start date to the end date in the sprouting / growth test of sea cucumber. FIG. 3 is a graph showing the germination rate (cotyledon appearance rate) of sea cucumber from the start date to the end date in the germination and growth test of sea cucumber. FIG. 4 is a graph showing the growth (average cotyledon length) after eel germination from the start date to the end date in the eel germination / growth test.

Hereinafter, the reformed soil for creating a brackish water ammo field of the present invention, a method for creating a brackish water ammo field using the same, and a method for growing sea bream in the brackish water area will be described in detail.
The improved soil for brackish water ammo field construction of the present invention removes dredged sand that is rich in nutrients such as nitrogen and phosphorus generated by dredging work in the sea area and fine particles in steel slag by-produced in the iron making process. It is a modified soil suitable for the construction of amamo fields in brackish water.

  Steel slag used in the present invention is a cheap and stable material that can be stably supplied, and steel slag such as converter slag, electric furnace slag, etc. produced as a by-product in a steelmaking process using a converter, electric furnace, etc. A blast furnace slow-cooled slag produced as a by-product in the pig iron manufacturing process using steel is preferable, and steel slag is preferable. This steel slag is mainly composed of a calcium silicate compound, can supply calcium ions over a long period of time, and has a specific gravity of 2.8 to 3.0 kg / L and sand ( It is considerably higher than 2.3 to 2.5 kg / L), and it is possible to prepare modified soil that can be used as a stable base material that is difficult to be washed away by mixing with dredged soil. Further, regarding the particle size of the steel slag, the steelmaking slag generally has a particle size in the range of 0 to 25 mm, and the particle size distribution is usually 2.36 mm or less 35%, 2.36 mm to 4.75 mm or less. Is 15%, more than 4.75 mm and less than 13.2 mm is 30%, more than 13.2 mm and less than 26.5 mm is 20%, and the blast furnace slag is usually in the range of 0 to 25 mm in particle size. The particle size distribution is almost the same as that of the steelmaking slag.

Here, for example, steelmaking slag among steel slags, the chemical composition is not particularly limited, but CaO content is 20 to 60% by mass, and f-CaO content is 0.2 to 20% by mass. %, And SiO ₂ content of 5 to 25% by mass, and for the particle size distribution, the particle size of 0.075 mm or less is 10% by mass or less and the particle size of more than 26.5 mm is 5% by mass or less is desirable (specified by the nominal size of the screen sieve specified in JIS Z 8801), and the 50% particle size (50% of the total particle size) is 5 mm or more and 15 mm or less. desirable. When the 50% particle size is about 5 to 15 mm, seaweeds such as sea eels can be stretched while entwining their roots, and the stability of the sea turtles is improved, and it is generally difficult to grow. Even in brackish water with a flow rate of 60 cm / s, it is possible to create an ammo field without being lost (anchor effect).

  In the present invention, the fine particle-removed steel slag mixed with dredged soil is a slag from which fine particles have been removed from the steel slag, and for the fine particles to be removed from the steel slag, the steel slag used Although it depends on the type and brackish water salinity of the brackish water area where the eelgrass field is constructed, it is usually a steel slag with a particle size of more than 2 mm obtained by removing fine particles with a particle size of 2 mm or less. Steel slag having a particle size of more than 5 mm obtained by removing fine particles of 5 mm or less, more preferably obtained by removing predetermined fine particles by washing classification using a soil washing classifier or the like. Washed steel slag. In particular, in the case of the washed steel slag obtained by the washing classification treatment, the particle size attached to the surface is removed to a fine particle size of μm or less, and the alkali elution reaction on the slag surface becomes more gentle.

  Then, when determining the fine particle content to be removed from the steel slag, the pore water is collected from the modified soil prepared by mixing the obtained fine particle-removed steel slag into the dredged soil. The measured pH value of the modified soil is less than 9.0, preferably in the weak alkali range of 7.4 or more and less than 9.0, and is not particularly limited. The method of measuring, the method of collecting and measuring pore water, etc. can be illustrated, Preferably, the brackish water salinity concentration of the amamo field construction area in the brackish water area is measured, and from the steel slag according to this brackish water salinity concentration It is good to determine the particle size of the fine particles to be removed, and furthermore, prepare a plurality of fine particle-removed steel slags from which different fine particles have been removed for the steel slag to be used. Removed steel slag is mixed with dredged soil Preparing a plurality of modified soils, placing each of the obtained modified soils in a plurality of simulated brackish waters adjusted to a plurality of salt concentrations, measuring the pH value of each modified soil, Create a calibration curve of salinity-modified soil pH value for the measured concentration and pH value of each modified soil. From the brackish water salinity concentration in the brackish water area, the modified soil pH value is less than the target value of 9.0. It is good to determine so that it may become an alkali range.

  Here, for the fine particle removal steel slag obtained by removing fine particles from steel slag, when the steel slag is steelmaking slag, it is called fine particle removal steelmaking slag or washed steelmaking slag, etc. When the steel slag is a blast furnace slow cooling slag, it is referred to as a fine particle removal blast furnace slow cooling slag, a cleaning blast furnace slow cooling slag, or the like.

  In the present invention, the mixing ratio of the fine-grain-removed steel slag in the modified soil is different depending on the type of steel slag, brackish water salinity concentration in the Amamo field construction area, etc., but preferably 10 mass% or more and 30 mass% In particular, in the case of steelmaking slag, it is preferably 10% by mass or more and 20% by mass or less. If the mixing ratio of the fine-grain-removed steel slag is 10% by mass or less, the anchor effect may be insufficient. Conversely, if it exceeds 30% by mass, the soil pH may exceed 9.0.

When the modified soil of the present invention is laid on the bottom sediment of an amamo field construction area in a brackish water area and seaweeds are cultivated with this modified soil to construct an ammo field, more specifically, the following first to first Method 3 is adopted.
That is, the first method is a method in which seaweed seeds are mixed in advance in the modified soil, and the obtained modified soil containing seeds is laid on the bottom sediment of the amamo field construction area in the brackish water area. In this first method, it is preferable that the seeds of seaweeds are not washed away from the modified soil obtained by mixing the seeds of seaweeds such as steel slag with fine grain removal and sea eels in dredged soil, and preferably germinate efficiently. The thickness of the modified soil to be laid is preferably 3 to 5 cm. Seeds of seaweeds such as sea cucumber can germinate easily at a depth of several centimeters from the surface. In addition, after germination, a modified soil mixed with seaweed seeds is laid in a thickness of 3 to 5 cm in order to increase the number of individuals by extending the rhizomes two-dimensionally at a depth of about 5 cm and branching. By doing so, germination and growth promotion of seaweeds such as sea bream can be promoted efficiently. In addition, when laying thicker than 5 cm, seeds existing in a place deeper than 5 cm are difficult to germinate, and there is a possibility that the formation efficiency of the eelgrass field is reduced.

  In the second method, the modified soil is put in a growth vessel capable of decomposing in brackish water, seeds of seaweeds are sown on the modified soil, and the modified soil on which the seeds are sown is placed in the brackish water area together with the growth vessel. In the third method, the modified soil is placed in a growth vessel that can be decomposed in seawater, seeds of seaweeds are sown on the modified soil, grown, and germinated. Is transplanted into the bottom sediment of brackish water together with the modified soil and the growth vessel. In these second and third methods, the seeding depth when seeding seaweed seeds on the modified soil is preferably 1 to 2 cm from the surface of the modified soil. Moreover, even if it germinates if it is shallower than this, there is a possibility that it may fall off from the modified soil.

  Furthermore, in the present invention, when the ammo field construction area where the ammo field is to be constructed exceeds 5 m which is not suitable for the growth of seagrasses such as sea eels, it is preferable to adjust the water depth to be suitable for growth by embankment. In this case, the type of embankment is not particularly limited, and may be soil or sand. Moreover, when the bottom sediment in the Amamo field construction area is very weak, it is preferable to lay modified soil after hard embankment. Examples of the hard embankment include blast furnace slag and a mixture of dredged earth and steel slag. In the latter case, if the mound is made of a solid embankment mixed with more than 30% by mass of steel slag in dredged sand, it is possible to lay the ammo field-forming modified soil on it.

In addition, the modified soil, which is a mixture of dredged soil and fine-grain-removed steel slag, contains a larger amount of nitrogen and phosphorus than the mixed soil of mountain sand and humus soil that has been widely used so far. Since it is abundantly contained, it is possible to further promote the germination of seeds of seaweeds such as sea lions and the growth of seedlings.
The present inventors have also confirmed that the supply of these nutrient salts is not hindered by the mixing of slag. In addition to dredged sand and fine-grain-removed steel slag, when dredged sand is in a brackish water area with little pollution and there is a lot of sand, etc. Humus soil may be added. The amount of such humus soil added is, for example, the seawater standard value for the cultivation of laver in which the concentration of nitrogen, phosphorus, etc. in the pore water is indicated by the aquaculture water standard (nitrogen: 0.1 mg / L, phosphorus: 0.014 mg / L) may be added at a concentration 10 times or more (considering dilution), that is, a nitrogen concentration of 1 mg / L or more and a phosphorus concentration of 0.14 mg / L or more.

  In the second and third methods, when seaweed seedlings such as eelgrass are raised on land, the growth of seaweed seedlings such as eelgrass can be promoted by using the modified soil of the present invention. The modified soil containing dredged sand and fine-particle-removed steel slag produced by the above method is laid in a growth container (for example, bat or cup) in a thickness of usually 3 cm to 15 cm, preferably 6 cm to 10 cm. Then, eel seeds are sown to a depth of about 1 to 2 cm from the surface. The seeded growth container is shielded from light and allowed to stand at 15 ° C. or less as much as possible. After confirming the germination of the seeds, the growth container is moved to light conditions to promote seedling growth. When seeding, seedlings are grown by placing the modified soil (slag mixed soil) in a plastic cup, a biodegradable plastic cup, a thin iron plate cup, etc. that can be decomposed in seawater. Also good. As a result, when transplanting seedlings to the eelgrass area construction area in brackish water, it can be easily transplanted after removing the cup in the water or with the cup attached. It can be transplanted without giving it, and it is possible to efficiently develop an ammo field.

The germination rate of seagrass seeds such as sea cucumbers in actual brackish waters is usually less than 60%, and the growth density is 30 strains / m ² or more in dense areas of natural sea eel fields. Therefore, it is preferable that the seeding density at the time of the Amamo field construction is 50 to 1000 grains / m ² .

  In the eelgrass field constructed according to the present invention, the pH in the soil can be kept below 9.0, and the eelgrass can be germinated normally and cultivated stably. In addition, if only the dredged sand was seeded, the seeds were washed away even if seedlings were sown, and even if they germinated, there was a problem that the roots were poor and washed away, but by containing steel slag, these washed away etc. The problem is suppressed.

[Verification experiment: Verification of the relationship between removed fine particles, salinity, and pH value]
The dredged material was collected from brackish water in Shima City, Mie Prefecture. As the steel slag, steelmaking slag (0-25 mm) having a particle size distribution of 0.075 mm or less and 10 mass% or less, 26.5 mm or more and 5 mass% or less, and 50% particle size of 5 mm or more and 15 mm or less was used. Furthermore, using the above steelmaking slag, three fine particle removal steelmaking slags (2-25 mm) obtained by removing fine particles of 2 mm or less, 5 mm or less, or 10 mm or less by sieving (5-25 mm), (5 -25 mm) and (10-25 mm).

The above three types of fine particle removal steelmaking slag are uniformly mixed in the above dredged soil so that the mixing ratio of the fine particle removal steelmaking slag becomes 20% by volume. Dredged sand + fine grain removal steel slag (2-25mm)), modified soil B (mineral sand + fine grain removed steel slag (5-25mm)), and modified soil C (mineral sand + fine grain removal) Steelmaking slag (10-25 mm) was prepared.
In addition, seawater having a salinity of 3.2% by mass is mixed in pure water at a ratio of 20% by volume, 50% by volume, and 80% by volume. Three types of simulated brackish water of 6 mass% and 2.56 mass% were prepared, and 5 L each of the above three types of simulated brackish water were placed in three 6 liter (L) tanks to prepare a brackish water tank.

  Next, nine 1 liter (L) disposable cups with a diameter of about 15 cm and a depth of about 20 cm are prepared, and each of the above-mentioned three modified soils A to C is placed in a total of nine disposable cups. Three disposable cups each containing 1 L of modified soil A (Group A), three disposable cups each containing 1 L of modified soil B (Group B), and 1 L of modified soil C each Prepared 3 disposable cups (group C).

  In each of the brackish water tanks containing the above three types of simulated brackish water prepared as described above, each one of the disposable cups of Group A, Group B, and Group C is put. After substituting in simulated brackish water in a brackish water tank and 14 days passed, the pH value and hardness of the modified soil in each disposable cup were examined. In this case, the pH value is measured by pulling up each disposable cup from each brackish water tank, removing the supernatant liquid from each disposable cup, and then opening a hole 2cm in diameter and 3cm in depth in the modified soil in each disposable cup. Is measured by measuring the pH of the interstitial water that has leached into the hole, and the hardness measurement for confirming the presence or absence of the solidification phenomenon is performed in each disposable cup after removing the supernatant liquid. Three points of the modified soil were measured using a Yamanaka hardness tester. In addition, the measurement of the pH value and hardness of the modified soil was repeated three times, and the average value was obtained and used as the measured value.

The result obtained in the verification experiment in which the relationship between the removed fine particle content, the salt content, and the pH value was examined was as shown in FIG.
As is clear from FIG. 1, in each modified soil after 14 days, there was a tendency for the pH to increase as the salinity decreased. Moreover, in the simulated brackish water having a salt concentration of 2.56% by mass, the pH is less than 9 in all the verification categories of the modified soils A to C, and in the simulated brackish water having a salt concentration of 1.6% by mass, the modified soil In the verification section of A, the pH was 9.3, whereas in the verification section of the modified soil B and the modified soil C, the pH was less than 9, and in the simulated brackish water with a salt concentration of 0.64% by mass The pH was 9 or more in all verification sections of the modified soils A to C.
Regarding the hardness of the modified soil after 14 days of simulated brackish water, solidification as measured by the Yamanaka hardness tester did not appear in all the verification sections of the modified soils A to C.

[Examples 1 and 2 and Comparative Examples 1 and 2]
1. Preparation of modified soil for brackish amamo ground construction The dredged soil was collected from brackish water in Mie Prefecture. Moreover, the steelmaking slag used in said verification experiment was used as steel slag. Furthermore, about this steelmaking slag, steelmaking slag is put into a bucket, tap water is put therein so that the volume ratio becomes 10 times or more, and fine particles of 2 mm or less are washed and removed in running water. Slag (2-25mm) was prepared.

The above-mentioned washed steelmaking slag is uniformly mixed at a ratio of 10% by volume and 20% by volume in the above dredged soil, and the modified soil of Example 1 (washed steelmaking slag 10) and the modified soil of Example 2 (washed) Steelmaking slag 20) was prepared.
In addition, the untreated steelmaking slag is uniformly mixed in the ratio of 10% by volume and 20% by volume in the dredged soil, and the modified soil (steelmaking slag 10) of Comparative Example 1 and the modified example 2 of Comparative Example 2 are mixed. Soil (steel slag 20) was prepared.
Furthermore, as a control group, a mixed soil composed of 60% by volume of cultured soil and 40% by volume of oyster shells used for the preparation of sea cucumber seedlings (modified soil of control group 1 (control group)) and only the above-mentioned dredged soil [control] 2 modified soil (bottom mud)) and, as a reference example, natural rocks with a particle size of 0 to 25 mm are mixed uniformly in the ratio of 10% by volume and 20% by volume in the above dredged soil. The modified soil of Example 1 (natural stone 10) and the modified soil of Reference Example 2 (natural stone 20) thus obtained were used.
Table 1 shows the modified soil for the amamo field preparation prepared in the above control group, examples, comparative examples, and reference examples.

2. Germination / growth test of sea cucumber under brackish water conditions The following germination / growth tests of sea bream were carried out using the modified soils prepared in each of the control plots, examples, comparative examples and reference examples. The seeds of sea cucumbers used for the germination and growth test of sea cucumbers were collected from a natural sea eel field in the vicinity of the place where dredged soil was collected.

About 4L of each modified soil is filled into a plastic jar measuring 272mm in length, 188mm in width and 79mm in depth. 30 seeds were sown each.
The troughs prepared in this way are arranged in the bottom of a 400 L FRP water tank, and in this water tank, the seawater collected at the tip of Hayama district in Kanagawa Prefecture is diluted to gradually start from a salt concentration of 2.2% by mass. And reducing the salt concentration to 1.5% by mass to create brackish water conditions and culturing under conditions of a water temperature of 10-12 ° C., a light intensity of 50-100 μmol / m ² / s, and a 12-hour light-dark cycle. The hardness of each modified soil is measured with a crust hardness meter (DIK-5561 made by Dairika Kogyo Co., Ltd.) every 6 to 14 days from the start date to the end date of the 118th day. The pore water was collected and the pH was measured, and further, the germination rate of the sea eel and the growth after germination (plant length) were measured.

The hardness of each modified soil was about 14 kPa in the modified soil of Comparative Example 2 (mixed with 20% by volume of untreated steel slag) at the end of the experiment, and some solidification was observed. In soil, it was below the detection limit, indicating that it hardly solidified.
Moreover, the measured result about the pH value of each modified soil is shown in FIG. As is clear from FIG. 2, in Comparative Examples 1 and 2, the pH of the modified soil changed at 9 or more, while other Examples 1 and 2, Control Zones 1 and 2, and Reference Example In 1 and 2, it was changing at around 8 which is almost the same as the pH in the water tank.

And the germination rate (cotyledon appearance rate) of the sea eel in each modified soil during the experiment period is shown in FIG. 3, and the change in the growth (average cotyledon length) after the germination of sea eel is shown in FIG.
Germination occurred 30 days after sowing, and then cotyledons were observed. On the 35th day, the germination rate was 90% or more in the control group 2, Examples 1 and 2, and Reference Examples 1 and 2, but 57% in Comparative Example 1 with 10% by volume of untreated steelmaking slag. In Comparative Example 2 with 20% by volume of untreated steelmaking slag, it was only 17%, which was clearly reduced, and it was found that the pH in the modified soil had an effect. In the control group 1, although the germination rate was 60% even though the pH in the soil was less than 9, the experiment showed that the nutrient concentration (nitrogen, phosphorus) in the soil was low. Inferred by post-end analysis.

In addition, as for the growth after germination, as in the germination rate of FIG. 3, all of the control plot 2, Examples 1 and 2, and Reference Examples 1 and 2 progressed smoothly. In Comparative Example 1 of% and Comparative Example 2 of 20% by volume of untreated steelmaking slag, growth stagnated remarkably. About the stagnation of the control ward 1, the reason similar to the fall of a germination rate can be considered.
In addition, since this test is not an experiment in a flowing water environment, in the case of the control section 2 using only dredged sand, Example 1 in which the cleaning steelmaking slag is 10% by volume, and Example 2 in which the cleaning steelmaking slag is 20% by volume. Showed a similar germination rate and growth (grass body length), but in a real environment with waves, the emergence rate and growth (grass) of the control group 2 due to the instability of the amamo field formed only with dredged sand. Body length) appears to be less than the results of Examples 1 and 2.

  From the above results, according to the modified soils of Examples 1 and 2, the particle size of the steelmaking slag mixed in the dredged sand is moderately improved, and thereby the pH value of the pore water of the modified soil in the brackish water area Is maintained in an alkaline region of less than 9, and it has been found that a stable eel field suitable for germination and growth of eelgrass can be created.

[Example 3: Test in actual brackish water area]
Steelmaking slag (0-25mm) was mixed at a rate of 40% by mass with the clay collected in the brackish water area of Shima City, Mie Prefecture to prepare a material for embankment. This embankment material was laid in an inner bay in the brackish water area of Shima City, Mie Prefecture, with a depth of 5 m (area 3 m x 3 m). On this embankment, each test soil shown in Table 1 (control group 2, Example 1, Comparative Example 1) was used to cover the soil so as to have a thickness of 5 cm (area 0.5 m × 0 for each test soil). .5m). Each test soil was premixed with eelgrass seeds at 50 grains / m ² .

Three months after the construction, in the control group 2 and in Example 1, germination of 10 strains corresponding to 80% of the sown seeds was confirmed. In contrast, in Comparative Example 1, only one strain (0.8%) could be confirmed.
A part of the cover soil (each test soil) was taken home during the diving survey, and the pH in the cover soil was measured in the laboratory. As a result, it was 7.6 in the control group 2, 8.3 in Example 1, and Comparative Example 1 It was 9.8. In the control group 2 and Example 1, there was no influence of pH from the embankment, and it was maintained below 9. On the other hand, in the comparative example 1, it became 9 or more and the alkali influence by the mixed steelmaking slag was confirmed.
The pH of the water around the embankment was 7.8, and no alkaline influence due to steelmaking slag in the embankment was confirmed. In addition, the embankment was solidified sufficiently, and no damage due to waves was observed.

Claims (16)

  A modified soil for brackish water ammo field construction for use in brackish water characterized by comprising a mixture of dredged sand and fine-grain-removed steel slag from which fine particles in steel slag have been removed.   The reformed soil for brackish water ammo field construction according to claim 1, wherein the fine-grain-removed steel slag is a steel slag from which fine-grains having a particle diameter of 2 mm or less have been removed.   The reformed soil for brackish water ammo field creation according to claim 1, wherein the fine-grain-removed steel slag is steel slag from which fine-grained particles having a particle diameter of 5 mm or less have been removed.   The said fine grain removal steel slag is steelmaking slag and / or blast furnace slow cooling slag from which the fine grain part in steelmaking slag and / or blast furnace slow cooling slag was removed, Any of Claims 1-3 characterized by the above-mentioned. Modified soil for building brackish water ammo fields according to claim 1.   The pH value in the said modified soil is less than 9.0, The modified soil for brackish water amamo field construction of any one of Claims 1-4 characterized by the above-mentioned. When laying modified soil on the bottom of brackish water and creating an ammo ground in brackish water,
Fine slag removed steel slag is prepared by removing fine particles in steel slag, and the modified soil obtained by mixing the prepared fine slag removed steel slag and dredged sand is prepared. A method for constructing a brackish amamo field, characterized by laying pelagic soil on the bottom sediment of the brackish water area to create an ammo field.   The brackish water ammo field according to claim 6, wherein before the modified soil is laid on the bottom of a brackish water area, the bottom sediment is filled and the modified soil is laid on the bank. How to build.   The said embankment is laid so that the water depth may be 5 m or less, The construction method of the brackish water ammo ground of Claim 7 characterized by the above-mentioned.   In preparing the fine-grain-removed steel slag, measure the brackish water salinity in the Amamo field construction area in brackish water, and determine the particle size of fine-grains to be removed from the steel slag according to the brackish-water salinity And the fine grain part of this determined particle diameter is removed from steel slag, The construction method of the brackish water ammo field of any one of Claims 6-8 characterized by the above-mentioned.   The particle size of the fine particles to be removed from the steel slag is based on a previously prepared calibration curve of salinity concentration-modified soil pH value, and the pH value of the modified soil is 9 from the brackish salt concentration in the brackish water area. The method for creating a brackish water ammo field according to claim 9, wherein the water is determined to be a weak alkali region less than 0.0.   The method for creating a brackish water ammo field according to any one of claims 6 to 10, wherein the fine-grain-removed steel slag is prepared by classification and / or washing treatment of the steel slag.   The steam according to any one of claims 6 to 11, wherein seaweed seeds are mixed in advance in the modified soil, and the obtained modified soil containing seeds is laid on the bottom sediment of a brackish water area. How to create a water eel   Put the modified soil in a breeding vessel capable of decomposing in brackish water, sow seeds of seaweeds on the modified soil, and arrange the modified soil sowed with seeds in the bottom of brackish water together with the growing vessel. The construction method of the brackish water ammo ground of any one of Claims 6-12 characterized by these.   14. The method for creating a brackish amamo field according to claim 13, wherein the seaweed seeds are sown from a surface of the modified soil to a depth of 1 to 2 cm.   The modified soil is put in a breeding vessel capable of decomposing in brackish water, seeds of seaweeds are sown on the modified soil, and the seedlings that have been grown and germinated are transplanted to the bottom sediment of the brackish water area together with the modified soil and the growing vessel. The method for constructing a brackish water ammo field according to claim 13 or 14. An eelgrass and / or a core eel are bred using the eelgrass field created by the cremation method according to any one of claims 6 to 15, wherein the eelgrass grows in a brackish water area.

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