JP4247285B2 - Method for regenerating submerged plant community and method for purifying water - Google Patents

Description

  The present invention relates to a method for regenerating a submerged plant community, typically a submerged plant community in a closed water area such as a lake or a pond, and a water purification technology using the submerged plant community.

  As measures against water pollution in closed water areas such as lakes and ponds, the Lake Water Quality Conservation Special Measures Law (hereinafter referred to as the Lake Law) was promulgated in 1984, and so on. Despite the fact that specific pollution source countermeasures have been implemented so far, in spite of this, there is almost no noticeable improvement in the water quality of closed waters such as designated lakes. On the other hand, the Lake Law was revised in June 2005, and the runoff water countermeasure area for reducing the surface load and the lakeside environment (lakeside plant) protection area for promoting the use of the natural purification function The lakeside vegetation zone conservation and restoration project for the improvement of water quality in closed water areas is expected to expand further in the future.

  In recent years, attempts have been made to use submerged plant communities to improve water quality in such closed waters. Specifically, the lakeside vegetation zone is composed of water-extracted plant zones such as reeds, floating leaf plant zones such as eagles, and submerged plant zones such as chromo, among which submerged plants are roots, stems, It is a plant where all leaves exist, and it has a function of uptake of nutrients such as nitrogen and phosphorus that promotes the occurrence of blue water, which causes water pollution, and a zooplankton such as Daphnia, which has a high water purification effect to prey on blue water. Since it has a hideout structure that protects from fish, it has a function of promoting the growth of these zooplanktons and a function of promoting sedimentation of suspended substances such as phytoplanktons, and thus has a large water purification function. And while other vegetation zones form a line at the edge of lakes and marshes, submerged plants can grow to a depth of about 4 m, so they can form a vast surface due to submerged plant communities, giving water quality. Great quantitative effect. Moreover, the submerged plant community is not only a water purification function as described above, but also a qualitative effect such as a waterfowl feed function, a spawning reef function for fishes, and a habitat function for fry and benthic animals. Is also big.

  In this way, submerged plants are superior to other vegetation zones in terms of water quality and ecosystems such as lakes and marshes, so by regenerating submerged plant communities, Can be expected to accelerate recovery.

  However, in submerged plants around Japan during the period of high economic growth, a large amount of nutrients flow in closed waters such as lakes and marshes, and the load increases. As a result, the light conditions indispensable for plant growth have deteriorated, and pesticides such as herbicides overspread on farmland flow into closed waters such as lakes and ponds. Most submerged plants have disappeared or declined, and many plant species are endangered to date. Especially in small and medium-sized lakes and ponds, most of the water areas have lost their submerged plants.

  Until now, the regulation of the amount of wastewater discharged from factories and workplaces and the amount of domestic wastewater and the control of agricultural chemicals have been made, so at present the main limiting factor for regenerating submerged plant communities is the underwater light environment. Waves are also known to be a limiting factor. As described above, the regeneration of submerged plant communities is limited by the light environment, because, if a large amount of phytoplankton, such as blue sea bream, is generated, the sunlight necessary for the growth of plants on the bottom does not reach the bottom. There is a reason why waves are limited to regeneration because large waves and lakes are affected by waves, and the submerged plants are rolled up before they firmly root their roots.

  Conventionally, as a method for regenerating submerged plant communities, a method has been implemented in which soil seed banks such as seeds and buds of native species that sleep in the bottom mud of the bottom of the water are sprinkled onto the bottom of the water. However, because the light environment in the water is poor, native species regenerate once in shallow places, but such shallow water depths can also grow drought plants such as coral and floating leaf plants, so ultimately they will compete for light. Loss and disappears again. Therefore, it is difficult to regenerate submerged plant communities by such a method.

On the other hand, in recent years, methods that combine the supply of submerged plants and economic light environment improvement techniques, such as a method using biomanipulation, a method using water level control, and a method using vegetation floating islands have been developed. Biomanipulation is a method of improving transparency by manipulating ecosystems such as removing fish that prey on zooplankton, such as daphnia, that prey on phytoplankton, such as sea lions, which are deteriorating the light environment. Regenerate submerged plant communities by combining methods such as seeding of soil seed banks and transplanting of seedlings. In addition, the water level control method supplies sunlight sufficient for the growth of submerged plants to the bottom of the water by reducing the water level of lakes and marshes, for example, to about 30 cm at the initial stage of regeneration of submerged plant communities. It is a method of regenerating a submerged plant community by raising it. In addition, as disclosed in the following patent document, the method using vegetation floating islands floats vegetation floating islands planted with water-extracted plants and vegetation floating islands planted with submerged plants on the surface of the water, and improves transparency on the floating islands of water-extracted plants. This is a method of cultivating a plant on floating vegetation floating islands, gradually increasing the cultivation water depth with improvement in transparency, and finally regenerating a submerged plant community on the bottom of the water area.
JP 2007-29058 A

  However, biomanipulation methods differ in ecosystems depending on the characteristics of water bodies such as lakes and marshes, so there are many cases where transparency cannot be improved, and removal of fish depends on water use restrictions such as fisheries. In large-scale lakes, it is very difficult to remove the majority of fish, and there is a problem that it may adversely affect the ecosystem. In addition, it is not suitable for lakes and marshes affected by waves.

  In addition, the water level control method is difficult to adopt in lakes and lakes that have water-use constraints such as fishing and agriculture, and is difficult to control in large-scale lakes. .

  In addition, the method using vegetation floating islands is hardly affected by water use restrictions, and there is a certain amount of wave-dissipating effect on waves, and it is an economically cheap and effective method, but when targeting large-scale lakes. Because of the increased number of vegetation floating islands installed, the cost may increase.

  The present invention has been made in view of the above-mentioned problems, and its technical problem is to regenerate submerged plant communities easily and at low cost even in large-scale lakes with little adverse effect on the ecosystem. Therefore, this is to purify the water quality of the closed water area.

As a means for effectively solving the technical problem described above, the method for regenerating a submerged plant community according to the invention of claim 1 is provided with an enclosure for isolating a part of the water area from other parts in the water area. After improving the transparency of the isolated water area, grow a submerged plant in the isolated water area, and when the submerged plant community has grown to a predetermined area in the isolated water area, the enclosure The process of expanding the area of the water area to be isolated as appropriate and subsequently growing the submerged plant is repeated. According to this method, by enclosing a part of the water area with an enclosure that isolates a part from other parts, cultivating a submerged plant, polluted water around which the phytoplankton such as the sea bream was generated or phytoplankton such as the sea bream is generated. Since it is possible to prevent the inflow of polluted water around the water, and to block the waves, it is possible to reliably grow submerged plants in the enclosure to form a community, and to gradually expand the prosperous area by the enclosure.

  The method for regenerating a submerged plant community according to the invention of claim 2 is the method of claim 1, wherein the enclosure surrounds a depth of 50 cm or more from the water surface.

  The method for regenerating a submerged plant community according to claim 3 is the method according to claim 1, wherein the enclosure surrounds the water surface to the bottom of the water.

  The method for regenerating a submerged plant community according to the invention of claim 4 is the method of claim 1, wherein the enclosure is made of a material that does not pass particles having a particle size of 2 μm or more. If a material of such a material is used, phytoplankton such as a giant sea bream can hardly pass.

  According to a fifth aspect of the present invention, there is provided a method for regenerating a submerged plant community, wherein the enclosure is made of a material having a water shielding property. Using such materials dissolves substances that adversely affect the growth of submerged plants, such as polluted water that contains nitrogen and phosphorus in very high concentrations and is prone to the occurrence of watermelon, detergents, and agricultural chemicals. It can effectively block contaminated water from entering the enclosure.

  A method for regenerating a submerged plant community according to claim 6 is the method according to claim 1, wherein the enclosure is a float for supporting the enclosure body and the upper part of the enclosure body on the water surface or the water surface. And a seat anchor for connecting the lower part of the enclosure main body to the bottom of the water and a float anchor for connecting the float to the bottom of the water.

  A method for regenerating a submerged plant community according to claim 7 is the method according to claim 1, wherein the enclosure includes an enclosure main body, a support frame for fixing the enclosure main body, and a lower portion of the enclosure main body. It consists of a seat anchor fixed to the bottom of the water.

  Further, the method for regenerating a submerged plant community according to the invention of claim 8 is the method of claim 1, wherein the enlargement of the enclosure is caused by the subsidence in the enclosure relative to the area of the water area isolated by the enclosure. The occupation area of the plant community is ensured 10 to 40%.

  Moreover, the water quality purification method according to the invention of claim 9 purifies the water quality of the closed water area by the submerged plant community regenerated by any one of claims 1-8.

  According to the present invention, it is possible to easily regenerate a submerged plant community even in a water area with a large wave effect or in a large-scale lake, and it does not require a physicochemical apparatus such as a large plant or a medicine. Therefore, it is possible to regenerate submerged plant communities at low cost without adversely affecting the ecosystem of closed waters such as lakes.

  Moreover, according to this invention, the water quality of closed water areas, such as a lake, can be purified effectively by reproduction | regeneration of a submerged plant community. Moreover, by regenerating submerged plant communities, it not only purifies water quality, but also functions as a waterfowl food, zooplankton hideout function such as daphnia that removes sea cucumbers, spawning reef functions for fishes, and a habitat function for fry and benthic animals. The ecosystem can also be expected to recover.

  Hereinafter, preferred embodiments of a method for regenerating a submerged plant community and a method for purifying water according to the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing the present invention in the order of steps, FIG. 2 is a perspective view and a side view showing an example of a structure of an enclosure applied in the present invention, and FIG. 3 is another structure of the enclosure 1 applied in the present invention. FIG. 4 is a side view showing a method for determining the size of the enclosure 1 at the initial installation, and FIG. 5 is a plan view of a lake showing an initial state in which the enclosure is installed in the present invention. FIG. 6 and FIG. 6 are plan views of lakes and marshes showing a state in which submerged plants have grown in the enclosure in the present invention. FIG. 7 is a plan view of lakes and marshes showing a state in which submerged plant communities have been regenerated in the present invention.

  In the method of the present invention, first, as shown in FIG. 1 (A), first, a part of the water area (hereinafter referred to as an isolated water body) is transferred to another part ( The enclosure 1 isolated from b) is set up and the submerged plant 2 is grown in the isolated water area a.

Since the isolated water field a by the enclosure 1 at the initial installation has a low water quality due to phytoplankton such as blue-green algae, in order to reliably regenerate the submerged plant 2 in the isolated water field a, the transparency of the isolated water field a It is necessary to supply the submerged plant 2 after improving . As a method for improving the transparency in this case, any method is used as long as it is not a method using a drug or the like that inhibits the growth of the submerged plant 2 because the area of the isolated water boundary a by the enclosure 1 at the initial installation is small. It doesn't matter. For example, a biomanipulation method, a water level control method, a vegetation floating island method, a method using a water purification device, a method using a small plant, or a method using a small plant may be used. You may use the method of supplying and replacing with polluted water.

  As a method for supplying the submerged plant 2 into the isolated water body a by the enclosure 1, there are local species remaining in the target water area, rivers flowing into the target water area, rivers flowing out of the target water area, and the like. Methods such as attaching weights to seeds that grow naturally in rivers in the water area, or using vegetation floating islands, or seeds of native species that sleep in the bottom mud of the water area or soil seeds such as sprouts It is also possible to adopt a method of rolling out the bank to the bottom of the water.

  The enclosure 1 may enclose four sides of the isolated water boundary a, or may be a method of enclosing the other three sides with the shore c as one side as shown in FIG. The size of the isolated water boundary a is not particularly limited, but is preferably set according to the structure in which the light conditions are preferable, the regeneration target scale of the submerged plant 2 and the regeneration period.

  In addition, it is a cyanobacteria generally called blue-green algae that most deteriorates the transparency of the water area among phytoplanktons, and these blue-green algae are generated in the form of powder on the water surface. For this reason, even in a structure in which a sheet or the like is suspended 50 cm or more deeper than the water surface on a floating body floated on the water surface, the effect of maintaining the transparency in the isolated water boundary a higher than the external water boundary b can be obtained. Since phytoplankton can be distributed at a deeper water depth, it is most preferable to have a structure that surrounds the water surface to the bottom of the water.

  The structure of the enclosure 1 may be any structure as long as it does not allow the contaminated water of the external water body b in which a large amount of phytoplankton such as sea cucumber is generated to flow into the isolated water field a. For example, as will be described later, a method of enclosing with a steel sheet pile, a wooden board, a pile, a water-impervious sheet, or the like used in civil engineering work is conceivable. Moreover, since most of the size distribution of phytoplankton (80% or more) is generally 2 to 200 μm, it is also preferable to surround with a film or sheet made of a material that is permeable and does not allow particles with a particle size of 2 μm or more to pass through. It is possible to prevent the water contaminated with phytoplankton such as the sea cucumber from flowing into the isolated water zone a. In other words, in order to prevent the polluted water that has been generated from flowing into the isolated water zone a, it is desirable to enclose it with something that cannot pass particles of 2 μm or larger. For example, when there is a drain outlet nearby, In order to prevent contaminated water containing very high concentrations of nitrogen and phosphorus that are likely to be generated and contaminated water in which substances that adversely affect the growth of submerged plants, such as detergents or agricultural chemicals, from flowing into the isolated water zone a, It is desirable to select a water-impervious material.

  As a specific example, for example, the enclosure 1 illustrated in FIG. 2 includes an enclosure main body 11 that surrounds a part of the water area (isolated water boundary a) and isolates it from the other part (external water boundary b), and the enclosure main body. The float 12 for supporting the upper part of the water 11 on the water surface WL or the water surface WL, the seat anchor 13 for connecting the lower part of the enclosure body 11 to the water bottom G, and the float 12 connected to the water bottom via a rope or wire 14 The float anchor 15

  In this configuration, the enclosure body 11 may be made of any material as long as it is a film or sheet that does not allow water to pass through or is permeable to water but does not pass particles of 2 μm or more. For example, generally there are synthetic rubber, vinyl chloride, polyester, polyethylene, asphalt type, bentonite type as the water shielding sheet material, so its material, thickness depending on conditions such as wave, wind, flow velocity etc. in the target water area Is preferably selected.

  The float 12 may be of any material or type as long as it has a buoyancy that can support the weight of the enclosure body 11. For example, a hollow plastic frame, a buoy made of foamed polystyrene or foamed vinyl chloride, or a hollow tubular shape may be used, but it is preferable to select a frame that does not easily break.

  The seat anchor 13 may be made of any material as long as the enclosure main body 11 is not separated from the water bottom G due to waves in the target water area, flow velocity, buoyancy of the enclosure main body 11 and the like. For example, a steel chain, a steel rod or tube, a steel weight, a sandbag filled with gravel, or the like can be suitably used.

  The float anchor 15 is fixed to the bottom G, and may be any one that exhibits a fixing force so that the float 12 is not caused to flow by waves, winds, or flow velocities in the water area. For example, steel or concrete blocks, rivets, chains, sandbags, and the like can be suitably used.

  Further, if the enclosure 1 has a closed structure in which the ends of the float 12 and the enclosure body 11 are connected to surround the isolated water boundary a, when the enclosure 1 is expanded, the connecting portion is removed and a new expansion is performed. This is practical because you only need to add minutes. In addition, products that are already on the market as antifouling films, silt fences, and oil fences include floats and sheets that have a particle diameter of 5 μm or more that do not pass through silt. Such products may be used as long as they meet the conditions of physical water bodies.

  And, according to the structure shown in FIG. 2, the large civil engineering work hardly occurs and the expansion work and the removal work of the enclosure 1 are easy, but the enclosure main body is prevented from being swept away by wind, waves, and flow velocity. 11 and the float anchor 15 need to be firmly fixed.

  On the other hand, the enclosure 1 illustrated in FIG. 3 is assembled with an enclosure body 11 that surrounds a part of the water area (isolated water boundary a) and is isolated from the other part (external water boundary b), and a bar or pipe material. The frame includes a support frame 16 on which the enclosure body 11 is stretched and fixed, and a seat anchor 13 that fixes a lower portion of the enclosure body 11 to the water bottom G. As the enclosure main body 11, the same thing as the example of FIG. 2 demonstrated previously can be used.

  The bar material or pipe material constituting the support frame 16 is capable of supporting the enclosure body 11 and has sufficient and sufficient rigidity to be inserted into the water bottom (bottom mud) G, and does not deteriorate due to dissolution or decomposition in water. Any material such as steel, wood or plastic can be used. For example, a single tube may be assembled into a frame shape as illustrated with a single tube clamp or the like, and the enclosure main body 11 may be stretched over the frame. As the seat anchor 13, the same one as in the example of FIG. 2 described above can be selected.

  The enclosure 1 shown in FIG. 3 has a larger structure than that of FIG. 2, but a support frame 16 is assembled by firmly inserting a bar or pipe material into the bottom G, and the enclosure main body 11 is surrounded by the support frame 16. Therefore, a stable structure with high strength can be obtained.

  Therefore, it is preferable to select the structure as shown in FIG. 2 or the structure as shown in FIG. 3 according to the characteristics of the target water area. As still another example, the sheet may be assembled in a planar shape using a steel sheet pile or a wooden board.

As a method of determining the size of the enclosure 1 at the time of initial installation, regarding light conditions, in the case of deep water, if the area of the enclosure 1 at the time of initial installation is small, the sunlight S sufficient for the growth of the submerged plant 2 Therefore, it is preferable to obtain the initial length of one side of the enclosure 1 preferable for the growth of the submerged plant 2 by the following formula (1).

In this equation (1), θ is the south-central altitude at the time of spring equinox and autumn equinox. That is, since the submerged plants grow well from spring to autumn, as shown in FIG. 4, the equation (1) always shows the sun at 80% or more of the bottom of the water at the south and middle altitudes of the sun at the spring and autumn minutes. This is a desirable design condition for increasing the growth of the submerged plant 2 by being exposed to light S. For example, when θ = 54 °, if the height of enclosure 1 is 2 m in a water area with a water depth of 1.5 m, the desired initial length of one side of enclosure 1 is about 7.3 m or more, and enclosure 1 is square The area is about 53 m ² or more. However, when the material of the enclosure 1 is a material that allows the sunlight S to sufficiently pass therethrough, it is not necessary to make such a design.

Moreover, the preferable magnitude | size at the time of the initial installation of the enclosure 1 according to the reproduction | regeneration target scale and period of the submerged plant 2 can be guide | induced by following Formula (2) and (3).

  In the above formula (2), the area of the target water area is the area of the closed water area (lake L shown in FIGS. 5 to 7) targeted for the regeneration of the submerged plant community. The target regeneration rate is the rate at which submerged plant communities are regenerated in the target closed water area, that is, the target regeneration scale. This is the inflow to the target water area, the amount and quality of the effluent water, the residence time of the water area, and within the water area. It is most desirable to set in a water quality prediction model that takes into account the water flow, material circulation in the target water area, etc., but may be set to 10 to 40% with respect to the target water area. That is, if the submerged plant community is regenerated to occupy an area of 10 to 40% of the target water area, an effective water quality purification action can be expected.

  In the above formula (2), the number of expansions is a value obtained by multiplying the number of annual expansions by the target period and subtracting the first enclosure. The number of annual expansions varies depending on the plant species, the water quality of the target water area, bottom sediment conditions, etc., but it is generally preferable to set the number of annual expansions once or twice a year and at most three times a year.

Based on the above formulas (2) and (3), for example, assuming that the area of the target lake where the submerged plant is regenerated is 1 km ² (1,000,000 m ² ) and the set value is set as follows, The preferred size of the starting enclosure is 1,600 m ² .
Target water area: 1,000,000m ²
Target regeneration rate: 20%
Enlargement rate of enclosure: 5 times / time Target period: 5 years Expansion frequency: 1 time / year

  Returning to FIG. 1, in the isolated water area a by the enclosure 1 at the initial installation shown in FIG. 1 (A), the inflow of polluted water in which phytoplankton such as sea lions is generated is prevented by the enclosure 1. Moreover, since the waves are also effectively blocked by the enclosure 1, the growth of the submerged plant 2 is not hindered. Therefore, as shown in FIG. 1 (B), the submerged plants 2 will eventually grow in the isolated water boundary a to form a community.

  The period until the community of the submerged plant 2 grows over the entire surface of the isolated water area a by the enclosure 1 is the size of the enclosure 1 and the characteristics of the target closed water area (Lake L), such as water quality and bottom quality, Although it depends on the supply amount of the plant 2, etc., when the community of the submerged plant 2 grows over the entire surface of the isolated water boundary a, the enclosure 1 is expanded as shown in FIG. 1 (C) or FIG. In this case, the large enclosure 1 may be newly constructed, but it is economical to open the existing enclosure 1 and to connect the newly expanded portion of the connecting portion 1b to the opened connecting portion 1a. is there.

  At this time, it is most desirable to predict the extent of expansion by using a water quality prediction model or the like according to the characteristics of the closed water area, but the size setting of the enclosure 1 at the time of initial installation described above From the same idea, it is preferable to set the expansion rate to 2.5 to 10 so that the area occupied by the community with respect to the area of the isolated water boundary a after expansion is 10 to 40%. The reason is that, in the state where the area of the community of the submerged plant 2 occupies 10 to 40% of the whole, the transparency of the isolated water boundary a after expansion is effectively improved by the purification action by the community of the submerged plant 2. is there. When the expansion rate is set to a magnification exceeding this range, the occupied area of the community is too small, so the transparency of the isolated water boundary a deteriorated by expansion is difficult to improve, and is necessary and sufficient for the growth of the submerged plant 2. Since sunlight does not reach the bottom of the water, the expansion of the community is delayed, or in the worst case, the regenerated submerged plant community may disappear again.

  As described above, if the enclosure 1 is expanded so that the occupied area of the community with respect to the area of the isolated water boundary a after expansion is 10 to 40%, even if the water quality of the isolated water boundary a is temporarily deteriorated by the expansion, Since the transparency is immediately improved by the natural purification function of the submerged plant 2, the community of the submerged plant 2 in the isolated water area a whose area is expanded by the enclosure 1, as shown in FIG. Will expand.

  When the community of the submerged plant 2 grows in the whole area of the isolated water boundary a by the expanded enclosure 1, the enclosure 1 is expanded again and the community of the submerged plant 2 grows. And by repeating such a process, as shown in FIG. 7, finally in the closed water area (lake L), the community of the submerged plant 2 can be regenerated to the target reclaimed area. it can. After the settlement of the submerged plant 2 has expanded to the target regeneration area, even if the enclosure 1 is removed, the subsidence plant 2 community will not disappear because the natural purification function of the submerged plant 2 is high. Expand. Moreover, the water environment including the water quality and ecosystem of the target water area can be rapidly recovered by the community of the regenerated submerged plant 2.

It is explanatory drawing which shows this invention in process order. An example of the structure of the enclosure applied by this invention is shown, (A) is a perspective view, (B) is a side view. The other example of the structure of the enclosure applied by this invention is shown, (A) is a perspective view, (B) is a side view. It is a side view which shows the method of determining the magnitude | size at the time of the initial installation of the enclosure applied by this invention. It is a top view of the lake which shows the initial state which installed the enclosure in this invention. It is a top view of the lake which shows the state where the submerged plant grew in the enclosure in the present invention. It is a top view of the lake which shows the state where the submerged plant community was reproduced | regenerated in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Enclosure 1a, 1b Connection part 11 Enclosure main body 12 Float 13 Seat anchor 14 Rope or wire 15 Float anchor 16 Support frame 2 Submerged plant a Isolation water body (a part of water area)
b External water (other parts of water)
L Lake (closed water area)

Claims (9)

An enclosure for isolating a part of the water area from the other part is provided in the water area, and after improving the transparency of the isolated water area, a submerged plant is grown in the isolated water area, and the submerged plant When the community grows up to a predetermined area in the isolated water area, the area of the water area isolated by the enclosure is appropriately expanded and the process of continuously growing the submerged plant is repeated. How to play.   The method for regenerating a submerged plant community according to claim 1, wherein the enclosure surrounds a depth of 50 cm or more from the water surface.   The method for regenerating a submerged plant community according to claim 1, wherein the enclosure surrounds the water surface to the bottom of the water.   The method for regenerating a submerged plant community according to claim 1, wherein the enclosure is made of a material that does not pass particles having a particle diameter of 2 μm or more.   The method for regenerating a submerged plant community according to claim 1, wherein the enclosure is made of a material having water-impervious properties.   An enclosure is an enclosure body, a float for supporting the upper part of the enclosure body on the water surface or the water surface, a seat anchor for joining the lower part of the enclosure body to the bottom of the water, and a float anchor for joining the float to the bottom of the water The method for regenerating a submerged plant community according to claim 1.   The method for regenerating a submerged plant community according to claim 1, wherein the enclosure comprises an enclosure body, a support frame for fixing the enclosure body, and a seat anchor for fixing a lower portion of the enclosure body to the bottom of the water. .   The enlargement of the enclosure is characterized in that 10 to 40% of the occupied area of the submerged plant community in the enclosure is secured with respect to the area of the water area isolated by the enclosure. To regenerate submerged plant communities.   The water quality purification method characterized by purifying the water quality of a closed water area by the submerged plant community regenerated by the method in any one of Claims 1-8.

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