GB2563827A

GB2563827A - Aquatic vegetation restoration device and method

Info

Publication number: GB2563827A
Application number: GB1709892.2A
Authority: GB
Inventors: Pan Gang
Original assignee: Nottingham Trent University
Current assignee: Nottingham Trent University
Priority date: 2017-06-21
Filing date: 2017-06-21
Publication date: 2019-01-02
Anticipated expiration: 2037-06-21
Also published as: CN110831902A; WO2018234791A1; GB2563827B; CN110831902B; GB201709892D0

Abstract

An aquatic vegetation restoration device 2 comprises a solid body of particles comprising at least one of clay, sand and soil, the body further comprises at least one macrophyte or regenerative part of a macrophyte or comprises a connection point for connecting at least one macrophyte or regenerative part of a macrophyte, in use. Suitably, the solid body comprises compacted, compressed and/or sintered particles. The body can comprise a frame 4 with one or more apertures or cavities. The soil particles can be modified with an organic polymer. Preferably, the particles comprise a mixture of clay and one or both of sand and soil. The solid body may disintegrate in water. The regenerative plant part may be a seed 14, bud or root. At least one light source 12, 12, such as a chemiluminescent light source, may be connected to the solid body. An apparatus comprising a plurality of the devices and a method of growing or restoring one or more macrophytes in a body of water, such as a lake, are also claimed.

Description

AQUATIC VEGETATION RESTORATION DEVICE AND METHOD

Technical Field of the Invention

This invention relates to devices for initiating, assisting and maintaining growth and restoration of aquatic vegetation. The invention further relates to devices for reducing/preventing sediment resuspension, and to methods for achieving the same.

Background to the Invention

Destruction of aquatic vegetation in lakes and other bodies of water has become a major global environmental problem. Aquatic vegetation can be destroyed through direct contact with pollutants, dredging, or eutrophication of the body of water in which the aquatic vegetation is situated. In the case of vegetation destroyed by eutrophication, harmful algal blooms (HABs) often result in serious problems such as ecological function destruction and water deoxygenation, which create a non-viable environment for vegetative growth.

Cyanobacterial blooms caused by anthropogenic nutrient input to aquatic ecosystems are expanding worldwide, which is a serious threat to drinking water supplies, public health, integrity of food webs, and ecological and economic sustainability of freshwater ecosystems. Accordingly, reducing external nutrients loading has been recommended as the primary step to control cyanobacterial blooms in eutrophic ecosystems. However, some shallow eutrophic lakes may show little response to reduced external nutrient inputs due to the fact that internal recycling of nutrients in already enriched sediment strongly delay the recovery. Hence, effective inlake technologies together with appropriate management strategies are crucial for accelerating lake restoration. Among the in-lake technologies, restoration of submerged vegetation is of great importance for sediment remediation, prevention of sediment resuspension, increasing nutrient absorption, triggering a healthy food chain, and keeping the clarity of the water in comparison to the algae dominated turbid water condition. However, growth of plant seeds or roots in heavily eutrophic water often cannot succeed because the algal bloom blocks the sunlight required for the growth of submerged vegetation. So far submerged vegetation has only be restored in relatively clear water systems where light can penetrate to reach the sediment. A previously developed technology using particulate Modified Local Soil (MLS) has been partially successful in dealing with submerged macrophyte regeneration in heavily eutrophic water, by removing the algal blooms and increasing the water clarity. However, this technology is still subject to influence of resuspension of sediment and algal floes under strong wind or current conditions.

Another very difficult environmental/ecological issue in relation to lakes and other bodies of water is the prevention of invasive weeds. It is a very difficult challenge to restore indigenous vegetation species in natural waters, because they are often much more fragile than the invasive alien species and are less likely to survive low light and water pollution conditions. So far, very few technologies are available that can selectively provide favourable conditions for the indigenous species in aquatic systems where invasive weeds dominate in relatively large scale natural water systems.

As lake restoration projects are widely sponsored by government authorities and by landscape/enterprise industries, novel engineering methods for restoring submerged vegetation in eutrophic waters are in great demand.

At present, the main methods for remedying destruction and damage caused to lakes and restoring the ecological environment include: physical methods; chemical methods; and ecological methods. Physical methods include cutting off source pollution; constructing retention basins; diluting and improving water leaks; circulating water in lakes; dredging sediments; and removing algae. Chemical methods include sewage dephosphorization and phosphorous fixation. Ecological methods include restoration of macrophytes. However, all of these methods are rather expensive and some involve significant energy input and expenditure of resources. In addition, many of the aforesaid methods fail to provide ways of ensuring sufficient light levels are provided to the macrophytes being restored, leading to growth failure, and in some cases, re-eutrophication. For natural waters, a transparency of 1.30m - 73m, 0.73m - 40m and 0.4m below Secchi disk transparencies indicates eutrophication, moderate eutrophication and super-eutrophication, respectively, in lakes suffering from HABs.

There are methods which result in effective removal of HABs, such as those described in US 7,758,752B, which describes the application of powders or granules of modified local soils (MLS) to effectively improve the water transparency of lake water through algal flocculation on a large scale.

On the other hand, known techniques such as these described in US 7,758,752B, may result in lake water periodically or regularly suffering from resuspension of the sediment (MLS) used to achieve removing HABs. Such resuspension can severely hinder the growth and restoration of submerged macrophytes.

There are known macrophyte restoration techniques used in eutrophication lakes, such as: planting vanguard hydrophytes and seeding zooplankton to improve water clarity; constructing submerged macrophytes and emergent plants to improve local water environment; adding oxidants (such as algaecides) to improve water quality, etc. These techniques all suffer from disadvantages. In the case of planting vanguard submerged hydrophytes, it is difficult to sustain viable growing plants over a long period of time, especially if algae blooms are still being treated and light levels are still low at the bottom of lakes. In addition, delivery of submerged macrophytes is difficult and may result in lake beds having large quantities of unwanted delivery vehicles, such as plant pots or the like, being deposited on the lake bed, which adversely affects the lake environment.

It would therefore be advantageous to provide a solution to the problem of enabling effective restoration of submerged macrophytes (initiating, assisting and/or maintaining growth) in waters which are still relatively turbid, whether due to algae blooms or sediment suspension. It would furthermore be advantageous to provide a solution for the problem of providing a method for algae removal and water quality

improvement which mitigates re-suspension of sediments provided by the use of MLS or other sediment-producing materials.

It would also be advantageous to enable the selective restoration of some fragile indigenous macrophytes in polluted waters that will otherwise struggle to survive due to invasive species and/or adverse water conditions.

It is therefore an aim of embodiments of the present invention to overcome and mitigate at least one problem of the prior art described hereinabove.

Summary of the Invention

According to the first aspect of the invention there is provided an aquatic vegetation restoration device comprising a solid body of particles of at least one of clay, sand and soil, the body further comprising at least one macrophyte or regenerative part of a macrophyte or having a connection point for connecting at least one macrophyte or regenerative part of a macrophyte, in use.

The solid body may be a rigid body.

The solid body may comprise a unitary body or may comprise two or more parts connected to form the solid body.

The solid body may comprise compacted or compressed particles. The particles may be sintered particles, and thus may be lightly bonded to adjacent particles at particle boundaries, in some embodiments.

The solid body may comprise any suitable three-dimensional shaped body.

Exemplary shapes include cuboid, cubic, tetrahedral, cylindrical and spherical.

In some embodiments the solid body comprises a frame comprising a plurality of frame members configured to form the edges of a framework, which may be a

polyhedral framework, such as cuboid, cubic, tetrahedral or the like, for example. A solid body in the form of a frame is particularly useful as the frame allows full circulation of water through the body and thereby ensures that the water can contact a relatively large surface of the body at all times.

In some embodiments, the solid body comprises a tetrahedral frame.

The particles of clay and/or soil may have an average particle size of at least lpm, 2pm, 3pm, 4pm, 5pm, 6pm, 7pm, 8pm, 9pm, 10pm, 11pm, 12pm, 13pm, 14pm, 15pm, 17.5pm, 20pm, 25pm, 30pm, 35pm, 40pm, 45pm, 50pm, 75pm, 100pm, 200pm, 250pm, 500pm, or at least 1mm, for example.

The particles of clay and/or soil may have an average particle size of no more that 10mm, 9mm, 8mm, 7mm, 6mm, 5mm, 4.5mm, 4mm, 3.5mm, 3mm, 2.5mm or 2mm, for example.

The average particle size of the particles may be in the range of lpm to 5mm, 2pm to 4.5mm, 5pm to 4mm, 10pm to 3mm or 20pm to 2mm, for example, especially 20pm to 2mm.

The particles of clay, sand and/or soil may comprise materials local, or taken from, to the body of water to be treated.

The soil may comprise modified local soil. The modified local soil may include one or more of clays, sediment, sands and soil particles modified with at least one organic polymer or alum, or lanthanum. Suitable organic polymers include natural organic polymers selected from, chitosan, chitin, cellulose, alginate, fibroin, collagen, and derivatives thereof, for example. In some embodiments, the modified local soil comprises at least one clay, sand or soil modified with chitosan or chitin

In some embodiments, the particles comprise clay particles and either sand or soil particles. In some embodiments, the particles comprise sand particles and soil particles. In yet other embodiments the particles comprise clay, sand and soil particles.

In some embodiments, the particles comprise a mixture of clay and sand particles. The clay and sand particles are preferably present in a ratio of 100:1 to 1:100, such as between 50:1 and 1:1, 25:1 and 1.5:1 or between 15:1 and 2:1.

The solid body may further comprise an oxygen-releasing compound. The oxygen-releasing compound may release oxygen into the water in which the device is submerged in use, to enrich the water with oxygen. The oxygen-releasing compound may be selected from a peroxide, a percarbonate, or a combination thereof, or surface oxygen nano-microbubbles. The oxygen-releasing compound may comprise a zeolite comprising a peroxide and/or a percarbonate, or oxygen nano-microbubbles and may comprise a mixture of a zeolite and one or more of calcium peroxide, magnesium peroxide, calcium percarbonate and sodium percarbonate. The ratio of the oxygenreleasing compound to the total amount of particles, in the solid body, may be between 1:1 and 1:1000, for example.

The solid body may further comprise a phosphorus-fixing compound. The phosphorous-fixing compound may comprise a lanthanum compound, such as lanthanum chloride, or alum, for example. The ratio of phosphorus-fixing compound to particles may be between 1:100 and 1:100,000, for example.

The regenerative part of a macrophyte may comprise a seed, root, bud, tuber, rhizome, stem or any combination thereof, for example. In some embodiments, the body comprises at least one of seeds, roots and buds of a macrophyte and preferably all three of seeds, roots and buds.

The macrophyte or regenerative part of a macrophyte may be a macrophyte or part of a macrophyte selected from Vallisnerria spiralis L, Ceratophyllum demersum L, Myriophyllum Linn sp., Hydrilla Verticillata Royle, Potamogeton crispus L,

Valliant ex Linn, Potamogeton Malainus, Myriophyllum spicatum Linn, Ranunculus

Kauffmannii, Naias marina, Elodea crispa, Ranunculus aquatilis, Anagallis tenella,

Hippurus vulgaris, Scirpus cernuus, Scirpus isolepsis, Myriophyllum Brasiliensis and any other suitable species that can adapt to water quality, sediment conditions, temperature and depth. The specific species used in any particular device of the invention may be selected based on its compatibility with the water body in which it will grow, and will preferably be a local species to the water body, or to water bodies in the same aquatic environment, locality or biome.

In embodiments comprising a connection point for connecting the macrophyte or regenerative part of a macrophyte, the connection point may comprise a shelf, aperture, protrusion or any other suitable point. The connection point, in embodiments in which the solid body comprises a frame, may comprise one or more frame member per se, which may enable a regenerative part, such as a root, to wrap around the frame member.

The macrophyte or regenerative part of the macrophyte may be connected to the solid body, or may be mixed with the particles of the solid body prior to the formation of the solid body.

In preferred embodiments the solid body comprises a regenerative part of a macrophyte connected thereto.

The device may further comprise a light source connected to the solid body.

The light source may be unpowered and/or the light source may comprise no electrical power source. The light source may comprise a chemical light source. The light source may radiate light through chemical reaction of components within the light source, and thus may not comprise an external power source connected thereto. In preferred embodiments the light source may comprise a chemiluminescent light source, and may for example be a fluorescent light source or a phosphorescent light source.

Suitable chemiluminescent light sources include fluorescent or phosphorescent light- sticks or gio-sticks, for example those sold under the trade name LUMICA (RTM).

Suitable fluorophores for use in the light source may include 9,10- bis(phenylethynyl)anthracene, 1 -chloro-9,10-bis(phenylethynyl)anthracene, 2,4-di-tert- butylphenyl-l,4,5,8-tetracarboxynaphthalenediamide and 9,10-diphenylanthracene, for example.

Alternatively or additionally the light source may be connected to an external power source. The external power source may be a battery, solar panel or the like. The external power source may be connected to the light source via a connection means such as an electrically conductive wire, cable or the like, for example. The external power source may be arranged, in use to be located outside of the body of water into which the device of the invention is placed or submerged. Each light source may be connected to its own external power source connection means, or two or more light sources may be connected to the same connection means, for example, two or more light sources may be strung along a single electrically conductive wire or cable.

In other embodiments the light source may comprise an internal power source.

The light source may comprise a LED, OLED or the like. There may be more than one light source connected to the solid body. In some embodiments, the light source provides light transmission at one or more wavelengths which preferentially enhance growth of the macrophyte over any algae, or specific algae present in the water body in which the device is to be submerged. In some embodiments, there may be a plurality of LED or OLED lights, comprising a mixture of red, green and blue LED or OLED lights. The mixture of LED and OLED lights may be configured to transmit the correct wavelengths of light required for the regenerative plant parts to grow. For example, the LEDs or OLEDs may comprise a smaller percentage for blue LEDs or OLEDs (transmitting light in the range of 400-475mm).

The, or each, light source may be connected to any suitable power source, such as a battery.

In some embodiments, comprising two or more light sources (such as a mixture of red, green and blue LEDs or OLEDs), the light sources may be connected together, for example by a wire.

The aquatic vegetation restoration device may be connected to a locating device, arranged in use to enable location and removal of the aquatic vegetation restoration device or parts thereof during or after use of the device. The locating device may be connected to the light source. The locating device may comprise a floating device. The floating device may comprise the external power source. The floating device may be a buoy or water-borne transport such as a boat, raft or skiff, for example. The locating device may alternatively comprise a structural component which may be fixed in a desired location during use of the device. Suitable structural components may include poles, for example, of a size suitable to protrude from the body of water in which the device is used. The light source may be connected to the locating device by an elongate member, such as a wire, cable or rope, for example. For embodiments in which the light source requires no external power source, the elongate member may not be electrically conductive. Each light source may be connected to the locating device via its external power source connection means, when present.

Having an unpowered light source, such as a chemiluminescent light source, and which is connected to a locating device ensures that the light sources have no mechanical or electrical components which may fail, and which are able to be removed after use via the means connecting the light source to the locating device, after use, in order to remove the light source and avoid further polluting the body of water into which the devices of the invention are used.

In other embodiments the aquatic vegetation restoration devices of the invention may comprise an elongate member, such as a wire, cable or rope, for example, which is arranged in use to connect to a fixed structure adjacent to the body of water into which the devices are submerged. Fixed structures to which the elongate members may be attached include jetties, mooring rings, quayside structures and the like, for example.

The solid body may comprise attachment points for attaching at least one light source. The attachment points may comprise protrusions, hooks, indentations, or the like for example. In other embodiments the, or each, light source may be connected to the solid body via a separate connection means or device, such as an adhesive, for example, or may be bound to the body by way of a rope, wire, string or the like for example. In some embodiments, there is provided a device comprising two or more light sources connected to the body, each light source being coupled to adjacent light sources. Each light source may be located on the same wire, string or rope, for example.

The solid body may be a water-disintegrable solid body.

Thus, the solid body of the device may be configured to break into smaller pieces over time, when contacted with water. In some embodiments, the solid body may be configured to break down into its constituent particles over time. In this way, the solid body is arranged to break down, disintegrate or fragment when submerged in water, to provide a granular or particulate material that may form a layer (or capping material) on the water bed. The layer of pieces, granules or particles forms sediment that can assist in macrophyte growth and help to flocculate algae.

The solid body may be configured to break down, preferably into its constituent particles over a time period of at least 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 14 days, 21 days, 28 days, 30 days, 60 days or at least 90 days; preferably between 14 days and 150 days, and in some embodiments, may be between 21 days and 120 days.

Thus the solid body may change from a solid body to particulate, granules or pieces over time upon contact with water. The solid body may therefore be a water- disintegrable solid body.

The size of the solid body will depend on the specific requirements of its use.

Some applications of the devices of the invention may require relatively small devices, while others may require relatively large devices. In general, the solid body may independently have a length of at least 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm or 10cm, a width of at least 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm or 10cm and a height of at least 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm or 10cm. In some embodiments the length, width and height may be independently at least 25cm, 50cm, 100cm, 250cm, 500cm or 1000cm.

The weight and shape of the solid body of the device is such that once it is put located onto sediment on the bottom or bed of a body of water, it may prevent the resuspension of the sediment underneath it. In embodiments in which the solid body is water-disintegrable, after a certain period of time (days, weeks or months) it will merge with the sediment, and hence become environmentally friendly. In embodiments comprising attached light sources, the light sources can absorb light during the day or when light conditions in the water are good such as when the algal blooms are moving away, and emit light when it is dark or during bad light conditions such as when algal blooms are present in the local environment. Statistically, the devices of the invention will reduce the resuspension of the sediment and increase the local light conditions around the devices and hence create an environment for the restoration of submerged vegetation. The aquatic vegetation restoration device may comprise a plurality of solid bodies, each device being connected to a support structure.

There may be a single support structure to which all of the solid bodies are connected. Each solid body may be spaced apart from adjacent solid bodies along the support structure. For example, each solid body may be positioned at least 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 45cm, 60cm, 75cm or at least 100cm from any adjacent solid body.

In other embodiments, the support structure may comprise a net or other open matrix, and there may be at least one solid body located at each node of the net, for example.

In addition, each support structure may comprise at least one light source connected thereto, and in some embodiments the support structure may comprise the external power connection means of the light source, and may be connected to an external power source, as described hereinabove Each light source may be as described above for the first aspect of the invention, and may comprise a LED or OLED light source. Multiple light sources may be connected to each other via a wire, rope, string or the like. The support structure may therefore be used to deliver the solid bodies to the bed of any water, and provide a light source for the regenerative plant parts. Each solid body may comprise at least one light source and/or the support structure may comprise multiple light sources (such as one at each node of a net, for example).

In embodiments in which the solid body disintegrates over time, the support structure will eventually be free of solid bodies and may be removed, along with connected light sources, for subsequent re-use.

In other embodiments, the support structure may be biodegradable over time, and may degrade over time on contact with water. Thus, the support structure may be configured to degrade at the same rate as the solid bodies disintegrate, for example.

According to a second aspect of the invention there is provided an apparatus comprising a plurality of devices of the first aspect of the invention.

In some embodiments, the plurality of devices is connected together, directly or indirectly.

The apparatus of the second aspect of the invention may comprise at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or at least 100 devices.

The apparatus may comprise a plurality of devices connected to a floating structure, such as a boat, raft, skiff or buoy, for example.

In preferred embodiments, each device is connected to the floating structure by an elongate member. The elongate member may be a wire, cable or rope, for example, and is preferably electrically conductive. Each elongate support structure may be connected to the solid body of a device at one end thereof, and may be connected to the floating structure at the other end thereof. There may be a single floating structure connected to all devices, or there may be multiple floating structures each connected to one or more devices. The floating structure may comprise a power source and each light source may be connected to the power source.

At least some of the devices comprise a light source connected thereto, and all devices may comprise a light source.

In some embodiments of the apparatus of the second aspect of the invention, each device of the apparatus comprises a plurality of water-disintegrable solid bodies of solid particles of at least one of clay, sand and soil, the solid bodies being connected to at least one light source and at least one regenerative part of a macrophyte, and wherein each light source is optionally connected to a floating structure.

In embodiments of the first aspect of the invention utilising one or more support structures and multiple solid bodies, or in utilising an apparatus of the second aspect of the invention, a larger areas of water bed, such as a lake bed, may be covered in a single application.

In embodiments in which the solid bodies of the devices and apparatus of the first and second aspects of the invention disintegrate and provide sediment, the regenerative plant parts of the macrophytes will grow and roots thereof will spread in the sediment provided by the solid bodies. At the same time the remaining portions of the solid bodies will provide structural attachments, cover and a means to prevent or mitigate re-suspension of the sediment, in order to prevent further turbidity in the water.

According to a third aspect of the invention there is provided a method of delivering a regenerative plant part to the bed or bottom of a body of water, the method comprising the steps of locating the or each solid body of a device of the first aspect of the invention or an apparatus of the second aspect of the invention on the bed or bottom of the body of water and allowing the macrophyte or regenerative plant part thereof to grow.

The method may comprise disintegrating the solid body or bodies of each device over time upon contact with the water.

According to a fourth aspect of the invention there is provided a method of growing or restoring macrophytes on the bed or bottom of a body of water, the method comprising the steps of: a) providing at least one device of the first aspect of the invention or an apparatus of the second aspect of the invention comprising a macrophyte or a regenerative part of a macrophyte; b) submerging the or each solid body of the device or devices in the body of water; and c) allowing the macrophyte or regenerative part to regenerate or grow to provide macrophyte growth.

The method may comprise the step of attaching a light source to each body or bodies of the device or apparatus or to a support structure of the device. The method may comprise removing the light source(s) from the water after step c) and/or after the body or bodies of the device(s) has disintegrated to its constituent particles.

The body of the device(s) may comprise a water disintegrable body and the method may comprise disintegrating the solid body over time, after submersion in the water. This step may be performed at the same time as step c). The method may comprise disintegrating the body over a period of at least 15 days, 30 days, 45 days, 60 days, 75 days, 90 days, or more. The time taken to disintegrate the body or bodies may be adapted to ensure that sediment is provided by the particles of the disintegrated body over a time period which enables effective growth of the macrophyte in step c).

The method may comprise submerging multiple spaced apart devices or bodies of the devices of the first aspect of the invention, or multiple devices or bodies of the devices of the apparatus second aspect of the invention. The multiple devices or bodies may be arranged on the bottom or bed of the body of water in a defined pattern, such as a grid, and each body may be spaced apart as described hereinabove. The method may comprise submerging at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or at least 100 devices or bodies of the devices. The area of the bottom or bed of the body of water covered by the spaced apart bodies may be at least 50 m2, 100 m2, 200 m2, 500 m2, 750 m2or 1000 m2, for example.

The method may further comprise a step of adding a powder or granulate algae flocculent material to the water. The powder or granulate algae flocculent material may comprise particles of the same clay, sand and/or soil of the devices of the invention, or a different material. The flocculent material may be added to the water before step a), step b) or step c) or may be added after step c).

The method to restore submerged vegetation and to remediate the sediment is particularly effective when multiple devices are placed on the bottom or bed of a body of water in a pattern according to hydraulic and sedimentation conditions of the body of water, so that the resuspension and local light conditions of the area can be improved. It is possible to adjust the distance between each unit so that the reduction of resuspension of sediment and/or increase of the light conditions in the engineering area can be maximized. This method will allow the selective restoration of fragile indigenous macrophytes that will otherwise struggle to survive due to invasive species growth or bad water conditions.

Detailed Description of the Invention

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which:

Figure 1 is a perspective view of an embodiment of an aquatic vegetation restoration device of the first aspect of the invention;

Figure 2 is a perspective view of the embodiment shown in Figure 1 with an attached light source;

Figure 3 is an embodiment of an apparatus of the invention (which comprises multiple devices of the first aspect of the invention); and

Figure 4 illustrates disintegration of a second embodiment of a device of the first aspect of the invention, over time, when submerged in water; and

Figure 5 illustrates a side view of another embodiment of an apparatus of the second aspect of the invention (which comprises multiple devices of the first aspect of the invention), in use in a lake.

Referring firstly to Figure 1, an embodiment of an aquatic vegetation restoration device 2 is illustrated. The device 2 includes a solid body in the form of a tetrahedral frame 4 comprising three elongate struts 6, 6’, 6” connected at one end via a base 8, and connected together at the other end. The base 8 is a solid triangular base and the struts 6, 6’ and 6” extend from the three corners of the base 8. The base 8 includes an upper surface 10. Located on the upper surface 10 of the base 8 are regenerative parts of a macrophyte in the form of seeds 14, 14’. In the embodiments shown in Figure 1, the seeds 14, 14’ are lightly adhered to the upper surface 10 of the base 8. In alternative embodiments, the seeds 14, 14’ or other regenerative plant parts of a macrophyte (such as buds, roots etc.) may be entrapped within the cavity formed between the base 8 and the struts 6, 6’, 6”, for example by reducing the length of the struts or size of the base 8 to dimensions in which the seeds cannot exit. In yet further embodiments, regenerative parts of a macrophyte may be embedded within apertures or cavities formed into the solid body 4 of the device 2. It will be appreciated that there are many different ways of ensuring the regenerative parts of the macrophyte are securely connected to the device 2.

The solid body 4 comprises agglomerated and compacted particles of clay and sand. The clay and sand are present in a ratio of 10:1, and have an average particle size of 180 mesh.

The solid body 4 is formed using the following method:

Firstly the clay and sand particles are homogenously mixed.

Secondly, the mixture of particles is mixed with water for approximately 5 hours.

Thirdly, the wet mix of particles is heat treated using a low temperature treatment between 50-90°C for 12 hours.

Finally, the treated particle mixture is exposed to a high temperature baking at 1000°C for approximately 12 hours, in a mould shaped in the form of a tetrahedron, as shown in Figure 1.

The resultant solid body 4 comprises baked and compacted clay and sand particles in which the particles have an average particle size of 180 mesh.

In alternative embodiments, the clay:sand mixture may be replaced or enhanced with a Modified Local Soil (MLS), for example. Such a MLS may comprise solid particles collected from a lake bed for which macrophyte regeneration is desired. The MLS may be modified by mixing the MLS with an organic polymer, such as chitosan, chitin or the like, preferably in a ratio of 5:1 to 100:1 MLS:polymer.

Referring back to Figure 1, in alternative embodiments of the device 2 shown, an oxygenating agent may be added to the clay and soil mixture before the low or high temperature treatment. Suitable oxygenating agents include zeolite powder mixed with a percarbonate or a peroxide, such as sodium percarbonate. A phosphorus-fixation agent can also be added to the mixture of clay and sand. Suitable phosphorus-fixation agents include lanthanum compounds such as lanthanum chloride.

The seeds 14, 14’ may be seeds from any suitable macrophyte species, including Vallisneria Spiralis L seeds and Potamogeton Crispus L seeds, for example.

The seeds may undergo budding pre-treatment before addition to the device 2. In other embodiments a whole macrophyte may replace the seeds 14, 14’.

The ratio of the volume of seeds to clay and sand particles may be between 1:10 and 1:2, for example. The solid body 4 of the device 2 is designed to disintegrate upon prolonged contact with water. The baked and compacted particles of clay and sands comprising the solid body 4, when submerged in water, slowly disintegrates into its constituent particles, which may form powder or particulate sediment within the water into which the solid body 4 is submerged. Thus, the solid body 4 is water- disintegrable.

In use, the device 2 is submerged in a body of water for which regenerative restoration of macrophytes is desired. The device 2 is submerged until it reaches the bottom or bed of the body of water. In preferred uses the body of water will be a lake, and the device 2 will be submerged until it rests on the lake bed. On settling, the device begins to work in two ways. The seeds 14, 14’ will begin to grow into macrophytes (and if an oxygenating agent is also used in the device 2, the oxygenating agent will begin to release, oxygenating the water around the seeds 14, 14’, aiding growth and regeneration of the macrophytes). Secondly, the solid body 4 begins to disintegrate into its constituent particles, such that a particulate sediment of clay and sand is released. As the released sediment is at the bottom of the body of water, such as a lake bed, it quickly settles to create a capping layer over the lake bed. This capping layer may provide an effective cap against pollutants on the lake bed. In addition, the capping layer of sediment provides an anchoring point for root growth from the regenerating seeds 14, 14’. In addition, as roots grow from these seeds 14, 14’ they may grow around the base 8 or struts 6, 6’, 6” of the solid body 4, which therefore provides solid anchoring for the roots until they become more established on the bed or bottom of the body of water.

In time, the solid body 4 will completely disintegrate into its constituent particles, providing a sediment capping layer on the lake bed. The composition of the particles making up the solid body 4 can be tailored to provide a controlled disintegration to match the growth profile of the regenerative plant parts of the macrophyte located on the solid body 4. For example, if it is desired that the solid body 4 should disintegrate over a time period of between 30 days and 120 days, the ratio of clays to sand to clay may be adapted to provide such a product. In addition, local soil from a lake bed may be mixed with the clays and sands of the body 4 in order to provide the desired controlled disintegration time period.

Thus, the embodiment of the device 2 of the present invention shown in Figure 1 provides a physical-chemical-ecological combined method for improving water quality and enhancing the ecological restoration of eutrophic or post-eutrophic lakes using the device 2. During restoration of the body of water or lake, the regenerating macrophytes will rapidly and effectively improve water quality and prevent further build-up of algae (in the case of lakes prone to eutrophication). A second embodiment of an aquatic vegetation restoration device of the invention is shown in Figure 2. This device is very similar to the device 2 shown in

Figure 1 and like numerals represent like components.

The sole difference between the device 2 of Figure 2 and the device 2 of Figure 1 is that the device 2 of Figure 2 includes a pair of light sources attached to the solid body 4, in the form of LED lights 12, 12’, connected to struts 6, 6” of the solid body 4.

The LED lights 12, 12’ are connected to the struts 6, 6” via pins (not shown), bored into the struts 6, 6”. The LED lights 12, 12’ include an integral power source in the form of a battery. In addition, the LED lights 12, 12’ include multiple LED bulbs of varying colours, and may be programmed to provide light in wave lengths conducive to growth of the macrophytes from seeds 14, 14’, whilst being hostile to growth of any algae in the water in which the device 2 is submerged. The LED lights 12, 12’ may be switched on before submersion of the device 2 in a body of water, or may include electronic means to allow remote activation of the LED lights 12, 12’ after immersion of the device 2 in the water. Remote activation may also include remote deactivation, such that the lights 12, 12’ may be turned on and off when desired. Use of the device 2 of the embodiment shown in Figure 2 is identical to that of the device 2 shown in Figure 1, save that the LED lights 12, 12’ will be turned on

either before or during submersion of the device 2 in the body of water. The LED lights 12, 12’ provide a light source conducive to optimising growth of the macrophytes from seeds 14, 14’. When the solid body 4 disintegrates into its constituent particles, the LED lights 12, 12’ will either fall to the bottom/bed of the body of water, or in some embodiments may be adapted to float to the surface of the body of water. They may then be recovered accordingly. In other embodiments, the LED lights 12, 12’ may be connected to a wire, cable or the like, which is anchored outside of the body of water. When it is desired to retrieve the LED lights 12, 12’ a user may then reel in the wire or cable in order to obtain the LED lights 12, 12’.

Figure 3 illustrates an aquatic vegetation restoration apparatus 18 of the invention. The apparatus 18 comprises a cable 20 in which is located an electrically conductive wire (not shown). The cable 20 includes a number of aquatic vegetation restoration devices 2 of the first aspect of the invention, and as described hereinabove with reference to Figure 1. These devices 2 trail from the cable 18 via branch cables 23. The individual devices 2 are identical to those described for Figure 1 hereinabove, and include regenerative plant material in the form of seeds 14, 14’ (not shown).

In addition, the cable 20 has a number of light sources in the form of LED lights 22, 22a, 22b, 22c, 22d, directly attached to the cable and electrically connected thereto.

In use, the individual devices 2 act in the same manner as the device 2 of Figure 1. The cable 20 is lowered into a body of water and may be arranged to lie on the bottom or bed of the body of water, such as a lake bed, or may trail in the water (which may be effected by trailing the cable 20 from a floating device, for example).

The devices 2 will disintegrate over time as described hereinabove with reference to the embodiments shown in Figure 1, and at the same time the regenerative plant parts will regenerate and grow to provide macrophyte growth. The LED lights 22, 22a, 22b, 22c, 22d provide light at wavelengths suitable for enhancing or accelerating the macrophyte growth, whilst being relatively hostile to algal growth. The device 18 of

Figure 3 includes the advantage that each of the devices 2 are attached to the cable 20, via their respective branch cables 23, and multiple devices 2 may therefore be submerged at the same time, and located within a specific area of a body of water such that high priority areas may be covered with devices 2 in a single step. The cable 20 also provides an anchor point so that the devices 2 do not move with currents within the body of water, and are therefore maintained in the general area of a specified location within a lake. In an alternative embodiment to that shown in Figure 3, the cable 20 may be replaced with a net or mesh of cables or wires (including an electrically conductive component in some embodiments). The mesh or net includes nodes, and each node may have an aquatic vegetation restoration device 2 connected thereto, for example. In addition, light sources may be connected to the nodes or cable/wire portions. A net or mesh has an additional advantage that it may cover a wide area of a lake bed and disintegration of each device 2 would therefore enable a relatively uniform covering of capping material/sediment to cover a large area of the lake bed, for control of pollution and enhancement of macrophyte growth.

The devices 2 and apparatus 18 of Figures 1-3 may be used alone; or alternatively they may be used in conjunction with application of an algae flocculent.

The algae flocculent may comprise a powder or granules of modified local soil, which may be dispersed in the body of water into which the devices 2 and apparatus 18 are submerged. The algae flocculent may be applied before submersion of the devices 2 or apparatus 18, or at the same time, or afterwards. The use of an algae flocculent helps to ensure that particularly turbid waters, in which the turbidity is at least partly caused by algal bloom, may be cleared or mitigated before, during or after submersion of the devices 2, 18, in order to accelerate growth of the regenerative plant parts of the macrophyte connected to the devices 2 or apparatus 18. Nevertheless, the devices 2 or apparatus 18 can be used without an algae flocculent, especially when the devices 2, or apparatus 18 include a light source connected thereto, which ensures that an effective light source bathes the growing macrophyte material ensuring rapid growth which may otherwise not occur due to turbid water conditions and lack of sunlight.

Referring now to Figure 4, a third embodiment of an aquatic vegetation restoration device of the first aspect of the invention is shown in a test experiment, submerged in a beaker of water. The device is a solid body in the form of a disc, and comprises the same compacted and baked particles of sand and clay as described hereinabove for the device shown in Figures 1 and 2. Figure 4 illustrates disintegration of the device over a period of 30 days, with photographs indicating the extent of disintegration at day 1, day 15 and day 30. As can be seen from Figure 4, the device is relatively intact on day 1, and maintains its disc-like shape, but over the course of 30 days, begins to disintegrate into its constituent particles of clay and sand, until at day 30 the majority of the device has disintegrated, leaving a sediment of clay and sand and scattered larger pieces of device. Eventually even the scattered pieces of device would disintegrate into constituent particles if the device is left in the water for a further period of time.

Figure 5 illustrates a second embodiment of a aquatic vegetation restoration apparatus 30 of the second aspect of the invention, in use. The aquatic vegetation restoration apparatus 30 includes two devices 2 of the first aspect of the invention and the same numerals are used for the same components of the devices 2 as described above forthe devices of Figure 2. Thus, the devices 2 comprise a solid body 4 with connected light sources 12, 12’ and seeds 14 loaded into the cavity of each body 4.

The aquatic vegetation restoration apparatus 30 further comprises a number of combined support structure and external power connection means in the form of electrically conductive cables 24, attached to the light sources 12, 12’. Each light source 12, 12’ is attached to its own individual cable 24a, 24b and in the cables 24 are connected at their other end to a floating support device in the form of a boat 26. The boat 26 includes an external power source (not shown) which transmits power to the light sources 12, 12’ via the cables 24.

In use, the apparatus 30 is stored on the boat 26 resting on the surface 28 of a body of water until required for deployment. Deployment of the apparatus 30 consists of submerging the devices 2 in the body of polluted water (and./or water with resuspended sediment and/or algal bloom) until the solid bodies 4 of the devices 2 rests on the bottom or bed 29 of the body of water. The solid bodies 4 will trap any sediment beneath the bodies and thereby prevent its resuspension. As the devices 2 are submerged, the cables 24 extend from the boat 26 into the water. The cables 24 are connected to both the light sources 12, 12’ on the bodies 4, and to a power source on the boat 26. Power can then be sent from the power source to the light sources 12, 12’ to illuminate the area around the devices 2, to selectively encourage growth of the seeds 14 loaded into the bodies 4. The light sources may be powered to provide light during periods where the water is dark or cloudy, such as at night or when there is significant sediment resuspension, pollution or algal bloom; and may be turned off during daylight and/or periods when the water is clear. Alternatively, the light sources may be turned on for the entire duration when the bodies 4 are on the bottom 29 of the body of water.

The bodies 4 of the devices 2 are water disintegrable and will slowly disintegrate into their constituent particles over time, allowing the seeds 14 to germinate and for the resulting submerged macrophyte to take root and grow. The light sources 12, 12’ help to enable effective growth of the submerged macrophytes, along with any oxygenating agent in the material of the bodies 4, and the material of the bodies per se. As the bodies 4 disintegrate slowly, sediments resuspension is reduced, and the root structure of emerging macrophytes helps to prevent further resuspension by binding the particulate matter produced by the disintegrating bodies.

Once the bodies 4 have completely disintegrated and the regenerated plants have become established, the light sources 12, 12’ may be recovered by reeling in the cables 24 back to the boat, and storing the attached light sources 12, 12’ until further use is required.

In alternative embodiments of the apparatus 30 of Figure 5, the light sources may be unpowered light sources, such as chemiluminescent light sources, and the cables 24 may be wires, cables or ropes which are not electrically conducting. In such embodiments, the boat 26 does not require any power source.

The above embodiments are described by way of example only. Any variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. An aquatic vegetation restoration device comprising a solid body of particles comprising at least one of clay, sand and soil, the body further comprising at least one macrophyte or regenerative part of a macrophyte or comprising a connection point for connecting at least one macrophyte or regenerative part of a macrophyte, in use.

2. A device as claimed in claim 1, wherein the solid body comprises compacted, compressed and/or sintered particles.

3. A device as claimed in claim 1 or 2 wherein the solid body comprises a frame comprising a plurality of frame members.

4. A device as claimed in any one of claims 1 to 3 wherein the solid body comprises one or more apertures or cavities.

5. A device as claimed in claim 4 wherein a regenerative part is located in an aperture or cavity of the solid body.

6. A device as claimed in any preceding claim, wherein the particles have an average particle size of between 20pm and 20mm.

7. A device as claimed in any preceding claim wherein the soil comprises soil particles modified with an organic polymer.

8. A device as claimed in any preceding claim wherein the particles comprise a mixture of clay and one or both of sand and soil.

9. A device as claimed in any preceding claim, wherein the solid body is a water- disintegrable solid body.

10. A device as claimed in claim 9, wherein the water-disintegrable solid body disintegrates into its constituent particles over a time period of at least 15 days, on contact with water.

11. A device as claimed in any preceding claim wherein the regenerative plant part comprises a seed, bud or root.

12. A device as claimed in any preceding claim, further comprising at least one light source connected to the solid body.

13. A device as claimed in claim 12, wherein the light source is a chemiluminescent light source.

14. A device as claimed in claim 12 or 13, wherein the light source is connected to a means for enabling removal of the light source after use of the device, such as a rope, wire or cable.

15. An apparatus comprising a plurality of devices of any one of claims 1 to 14.

16. An apparatus as claimed in claim 15 wherein each device comprises a light source.

17. An apparatus as claimed in claim 16 wherein each light source is a chemiluminescent light source.

18. A method of growing or restoring one or more macrophytes in a body of water, the method comprising the steps of: a) providing at least one device of any one of claims 1 to 14 or an apparatus of any one of claim 15 to 17, comprising a macrophyte or regenerative part of a plant connected thereto; b) submerging the body or bodies of the device or apparatus in the body of water; and c) allowing the macrophyte or regenerative plant part or parts to regenerate or grow to provide macrophyte growth.

19. A method as claimed in claim 18, further comprising connecting a light source to the device or apparatus, and then illuminating the macrophyte or regenerative plant part after submersion of the device in step b).

20. A method as claimed in claim 18 or 19 wherein the or each body of the device or apparatus comprises a water-disintegrable body and the method comprises disintegrating the body over time, after submersion of the device in step b).

21. A method as claimed in claim 20, wherein disintegration of the or each body is performed for at least 15 days.

22. A method as claimed in any one of claims 18 to 21, further comprising a step of adding an algae flocculent material to the water.