CREATE A NATURAL POOL IN YOUR GARDEN
Replacing a few square meters of sanitized grass with a small aquatic universe animated by the flight of dragonflies, the frogs of frogs and the multicolored palette of irises, this is the original challenge that “Jeunes & Nature” launches you. At a time when roads, industrial zonings and vast cultivated areas distort the value of our landscapes and replace natural environments, the creation of natural oases in your garden constitutes an effective action to protect nature, a fascinating educational tool. for children of all ages as well as an incomparable aesthetic asset that is sure to brighten up the garden. Let's dig ponds! This little article will provide you with as many useful tips as possible for creating a natural pond in your garden. Read it carefully and do not hesitate to contact us for further information.
A SPACE RESERVED FOR NATURE A pond is a small body of still water reaching a depth of at most 1.5 meters. Who says NATURAL pond means that the intervention on the life of the aquatic environment will be limited to the strict minimum, in order to allow wild species to develop freely. By preferring to the introduction of exotic species the natural recolonization by plants and animals of our regions, we will quickly reach an ecological balance guaranteeing the good sanitary state and the good functioning of the aquatic environment. The respect of a few elementary principles will allow the spontaneous installation of a whole host of organisms belonging to the different levels of the food chain (herbivores, predators and decomposers), organisms which will take care of the maintenance of the pond themselves! The “natural ponds” action of Jeunes & Nature therefore advocates much more than the construction in the open air of a giant goldfish aquarium embellished by sophisticated play of light, also something else than the installation of a pond. concrete intended to accommodate water lilies, Japanese carps and other avatars of genetic engineering. Quite simply, let's give nature the opportunity to get out of its reserves and to express itself freely in our daily universe: let's spare it a small space in our garden.
BEFORE YOU BEGIN
Any plan to create a pond must be carefully considered. Before getting to work, it is important to ask yourself the following questions: Do I have the ideal location to create a pond?
To install a natural pond, it will be necessary to have a surface of at least 2 or 3 square meters benefiting from good conditions of sunshine. Am I ready to make a human and financial investment? The creation of a pond, even a small one, is in itself a small undertaking. The excavation will require moving sometimes large volumes of soil and, in the majority of cases, the installation of a waterproofing system for the land will prove to be necessary.
Am I ready to develop the surroundings of the site?
Ideally, the immediate surroundings of the pond should be somewhat developed in order to constitute a perimeter of protection around it and to guarantee the quality of the aquatic environment. The earth resulting from the digging will make it possible to create hilly surroundings, offering shelter to the fauna which will choose to take up residence in the pond (newts, various frogs, etc.).
Will young children come to play near the pond?
For young children, the presence of a pond in the garden will invariably be a sure attraction as well as a risk of drowning that should not be overlooked. It is up to everyone to assess the importance of this risk and install, if necessary, a protective fence around the wetland.
Herons can also come in this pond, if the basin is easy to access they will come to feast on your carp and other fish (I unfortunately had the experience) to grill? yes but the rendering is unattractive. Stretching peach threads across, crossing each other seems a good compromise. Otherwise decoys are sold, in order to deter the herons.
DESIGN YOUR MARE
That's it ! You are now ready to embark on the great adventure of the natural pond. Depending on the land you have, different types of ponds can be installed:
the land is relatively marshy (impermeable clay soil) and is fed by a water table flush with or close to the surface of the soil (located less than one meter deep in summer). In this particular case, which is certainly not the most frequent, you will be able to realize
inexpensively a pond fed directly by the aquifer. Its realization consists simply of digging a depression in the clay soil and does not require the installation of a waterproofing system. It is therefore a rather interesting concept because the pond thus created takes on a completely natural aspect; its plant colonization occurs spontaneously and very quickly by the surrounding plants. It may nevertheless present a risk of significant summer drying out. As is most often the case in our gardens, the land is dry and has no flush water table. In addition to the digging work, it will be compulsory here to waterproof the bottom and the side walls of the depression. Most of this document is devoted to the construction of this type of ponds.
When making the pond, a series of questions will arise. We will try to answer them in the following order:
where am I going to place the pond?
which dimensions and which shapes to choose?
how to make the pond practically (digging, waterproofing)?
how to arrange the surroundings of the pond?
how to promote plant and animal colonization?
how to maintain the pond?
CHOICE OF LOCATION
The pond must be set up in an open and sunny place (if possible, it will be exposed to the south and open to the east and west): light and heat are essential for the proper development of aquatic vegetation and for balance. biological pond. The pond will be dug away from trees insofar as the accumulation of dead leaves and especially conifer needles causes acidification, the appearance of a brownish color and excessive siltation of the water (phenomenon of eutrophication). Note, however, that it is always possible to have a net above the water to collect dead leaves in autumn. In addition, the root development of trees does not
will in no way facilitate earthworks and could later puncture or damage the waterproofing system. Other factors may still determine the choice of the location of
the future pond: for example, you can take advantage of an existing depression or a marshy area. Avoid placing the pond on a steep slope or in an area where it could be subject to landslides. On the other hand, it will fit very well near a scree or rockery. As far as possible, avoid placing it in the middle of the lawn and instead dig it out on the outskirts of the garden, not far from a more “wild” area (for example near a hedge or an area. not mowed which will be an ideal refuge for wildlife). To precisely delimit the location of the pond, it will also be necessary to keep in mind the fact that the outer edges of it must all be level, otherwise the water will escape from it like a plate to soup too leaning! Consequently, the general slope of the land should be as low as possible. If there is a slight difference in level, the outer perimeter of the pond will be aligned with the lowest point. The cavity will always be dug in dry land. It would indeed be illusory to want to build a side earth embankment to retain the tarpaulin: it would quickly collapse under the heavy weight of the water when the pond was filled.
THE SIZE, DEPTH AND PROFILE OF THE POOL
Above all, it is important to know that the SURFACE available for digging a pond is rarely a limiting factor: with 2 or 3 square meters, it is already possible to create a small harmonious aquatic environment capable of attracting a whole crowd of amphibians and fish. 'insects. Obviously,
the larger the size, the more the biological value of the site will increase through the diversification of vegetation and micro-habitats. To give an order of magnitude, know that the usual surface of a garden pond varies between 3 and 25 square meters for the smallest and
reaches a hundred square meters for the largest. It is up to everyone to assess the size of the pond according to their possibilities (financial cost, available space, ...).
The DEPTH and the SLOPE are two particularly important factors which will condition above all the quality of the pond, its ecological interest and its integration into the garden. You should know that the different species of aquatic plants each have their preferences in terms of depth
Thus, the botanist will distinguish:
The plants of the banks and marshy banks (forget-me-nots, mints, lysimaques, populations, sedges ...),
semi-aquatic plants, rooted in the mud, which protrude at most up to 50 cm deep (reeds, cattails, sagittarius, iris, water plantain, etc.),
floating plants whose leaves and flowers emerge on the surface of the water (water lilies, duckweed, pondweed, etc.),
Submerged plants , said to be oxygenating (callitriches, milfoils, elodea ...).
In order to allow the development of these different vegetation belts, it is important to create gently sloping banks. This also makes it possible to avoid landslides and to reduce, during severe frosts, the pressure of the ice on the walls of the pond; these banks also provide a convenient escape route for animals that have accidentally fallen into the pond.
Deeper areas of up to 80cm or even 120cm in depth are also important as they keep areas of open water devoid of aquatic vegetation. What is more, the deep areas provide shelter for the pond animals in the event of severe winter frost. In practice, we will try to dig gently sloping banks converging towards a deeper area. It is the north bank of the pond (= bank exposed to the south) which is the best exposed to solar radiation and which is therefore the most conducive to the development of vegetation. If the surface of the pond is relatively small, care should be taken to arrange this bank on a gentle slope or in steps, while the opposite bank may be steeper to reach a depth of around 80 cm.
Pond plants - Ecological categories.
Plants from the banks and marshy banks: Scattered rush, Reine-des-Prés,
Marsh population, Common Lysimachus.
Semi-aquatic plants: Sagittarius, Yellow Iris, Massette.
Floating plants: Duckweed, White water lily.
Submerged plants: Milfoil.
Choice of the profile of the pond.
As for the SHAPE of the pond, it will be varied, with CURVED and asymmetrical CONTOURS, but not too complicated (difficulties of realization). In fact, you should know that the more complicated the shape, the more “scraps” there will be in the waterproofing material (cutouts and pieces of unused tarpaulin).
The waterproofing system
Here we come to the most crucial step, namely the realization of the waterproof bowl. To do this, you will have to dig a depression, adjust its profile and place a coating to waterproof the bottom and walls of the pond. We will focus here on ponds which are waterproofed by a plastic cover. Other systems exist but will not be detailed here. Let us simply quote the coating by a layer of clay (heavy to handle and impermeability not ensured) and the ponds whose walls and the bottom are made using rigid materials - concrete and polyesters - whose installation is very delicate and the rather prohibitive cost.
So shallow depth over the entire surface of the pond. Significant risk of summer drying out and invasion by vegetation.
High depth over the entire surface of the pond. Development of aquatic vegetation on the banks and in shallow areas made impossible.
A compromise between the two preceding situations makes it possible to reconcile the advantages of the two types of ponds. It is the PVC COVER which clearly constitutes the best quality / price ratio. 0.5 to 2 mm thick, black or green in color, this flexible material is perfectly waterproof. However, you should avoid walking with shoes on the tarpaulin. Its lifespan is generally guaranteed by the manufacturer for a period exceeding 10 years. Its price fluctuates around 5 euros per square meter. This type of tarpaulin is easily found in most supermarkets as well as in specialized shops (nurserymen). The principle of the design of ponds waterproofed by a tarpaulin of this type is relatively simple. After having dug a depression in the ground, one will successively lay out on the walls of this one: a layer of 5 cm of sand (optional coating layer for loose soils, but essential for stony soils),
the plastic sheet, a thin layer of earth which will constitute the “substrate” of the pond and in which the vegetation will be able to take root. Please note, when calculating the dimensions of the pond, do not forget to add about ten additional centimeters to take into account the cumulative thickness of these different layers.
- earthmoving tools: spades, shovels, pickaxes, etc.,
- mason's level,
- wheelbarrow (to transport the earth),
- waterproof PVC or butyl rubber tarpaulin,
- sand and clay (possibly).
We can calculate the dimensions of the tarpaulin to buy by performing the following calculation:
Length = maximum length of the pond + 2 times maximum depth
Width = maximum width of the pond + 2 times maximum depth
REALIZATION OF THE POOL AND INSTALLATION:
The outer perimeter of the pond is precisely delimited with a rope, stakes ...
Earthworks are carried out with appropriate tools. The profile of the banks and walls is produced according to the predefined plans (use a level), taking into account the additional 10 cm associated with the thickness of the different layers. When digging, be careful not to meet and damage a cable or a pipe that could cross the garden!
After removing all the protruding elements (stones, roots ...) that could puncture the tarpaulin, we tamp and smooth the entire surface of the depression. In the case of stony soils, the bottom and the walls are lined, as far as possible, with a layer of sand 5 centimeters thick. The tarpaulin is placed on the walls of the cavity, following the shape of the latter. The protruding folds will be eliminated by folding the sheet sections one below the other. If this work requires walking on the tarpaulin, it will be done with bare feet to limit the risk of perforation of the plastic material.
CAUTION: the cover must only be fixed after filling with water. In this way, it will perfectly match the shape of the cavity, which will avoid tensions and tears. Ideally, you should fill the pond with water for the first time and then empty it. This operation allows the plastic material to be cleaned of any chemical substances covering it. We can also take advantage of this operation to correct the shape of the depression, enhance certain edges, etc. The pond can finally be filled with water. Rainwater is preferred to tap water insofar as the latter is too rich in mineral elements (chlorine, nitrates, carbonates, etc.). Too rich water can indeed cause various biological imbalances, such as a rapid invasion of the water by green algae, the covering of aquatic vegetation by a whitish film of limestone, etc. In our regions, depending on the season, rainwater will have filled the pond within a period of between a few weeks and a few months. If you want to speed up the process, you can possibly use water from a well or a cistern (beware, however, of water that has trickled onto metal sheets or that has stagnated too long in a cistern). It is then necessary to cut the edges of the plastic sheet, leaving an additional margin of 40 cm all around the body of water and secure it securely on the sides. Different possibilities exist at this level: they are detailed in the section dealing with the development of the surroundings of the pond. At the bottom of the pond, a thin layer of soil can be dispersed - a maximum of 5 cm thick to provide a first substrate for the vegetation. The soil in question should not be too rich in organic matter (avoid using potting soil or compost soil). You can, for example, work with a 50/50 mixture of sand and clay. Warning
not to put too much substrate: once the aquatic vegetation is installed, the thickness of the mud will only increase over time, which leads to a gradual filling of the pond. The plants will be arranged according to their ecological preferences (water depth!). They can be planted directly in the substrate or in a pot. This last possibility is preferable for plants provided with a powerful root system which would risk puncturing the tarpaulin and for plants whose development it is desired to be able to easily control.
DEVELOPMENT OF THE AREAS OF THE POND
Securing the tarpaulin
It is important that the tarpaulin - and especially the edges - are not exposed to direct sunlight because after a few years the plastic material (PVC) hardens and splits under the influence of UV The best way to hide the tarpaulin and quickly integrating the pond into the garden consists of hiding the edges of it under the grass. To do this, simply incise the earth horizontally at the base of the root system of the lawn, along the length of a spade iron and all around the perimeter of the cavity, before sliding the edge of the tarpaulin into the slit thus made. If the shore is made on a gentle slope just before joining the grass, it is possible to create a swampy area that will make the transition between the lawn and the water feature. The banks can then be developed and possibly consolidated with flat stones.
The volume of soil removed from the hole can be relatively large. If one does not want to have to excessively modify the appearance of the garden, the soil will be eliminated. But we can very well use it to spread it on one side of the pond - to the north if possible - so as to create a higher shore which will extend the marshy area, benefit from good sunshine and protect the pond against weathering. Pioneer plants will settle there spontaneously and we can eventually plant some low bushes (not too much: beware of falling leaves in the pond). The opposite bank (south bank), generally more abrupt, could be studied in order to provide easy access to the pond and to strengthen the bank. We can thus lay along it a wooden joist, some flat stones, etc.
PLANT POPULATION OF THE MARE
Whether plants or animals, IT IS EXCLUDED TO INTRODUCE
IN A NATURAL POOL OF EXOTIC SPECIES , not adapted to our climatic conditions. First of all, their chances of installation are relatively reduced and, even if they succeed, they risk spreading in nature, entering into competition with species from our regions and disrupting the functioning of our regions. ecosystems. We remind once again that the population of the pond by local species constitutes the best guarantee of its good biological balance.
Spontaneous colonization by aquatic vegetation of an artificially created pond is possible if silt from another body of water is used as a substrate and if there are other wetlands in the immediate environment of the pond. pond. But this recolonization will often be very slow. This is why we recommend you to plant and sow yourself native plants belonging to the different ecological categories (plants of marshy, semi-aquatic, floating and submerged banks. It is possible to introduce at least 1 to 2 species from each category into the pond. These plants will guarantee the aesthetic appearance of the pond and allow the oxygenation of the water, an essential condition for the development of animal life. the importance of submerged plants which provide the water with most of its oxygen supply. The ideal supply of aquatic plants consists in fetching seeds, plants and cuttings from other followers of the natural pond. get plants from specialized nurserymen, while ensuring that we only buy plants from our regions. By doing so, we will not impoverish our wild wetlands q ui host enough
many species in the process of rarefaction, some of which are also protected by law (this is the case of our two species of water lilies). Remember also that the law prohibits any removal of plants, whatever they are, in a nature reserve. Too many aquatic plants should not be introduced into the pond as most of them spread and spread very quickly. The plants from the banks and marshy banks will be sown or transplanted from the end of the fall to the beginning of the spring while the other aquatic plants will be transplanted later, from the month of April to the month of July, from seedlings or plants. cuttings. Care should be taken to respect the specific requirements of the different species in terms of water depth, sunshine, etc. These requirements as well as the mode of transplantation (seed, whole plant, cutting, stump division, rhizome (= large underground stem))
If very little substrate has been placed on the tarpaulin, make sure that the roots of the plants are surrounded by a clod of earth before placing them in the pond. It will still be necessary to ballast the roots of certain floating plants - with a stone - to ensure that they are anchored to the bottom of the pond.
Duckweed Lemna minor Covering Plant
The sagittarius, the native yellow and white water lilies are partially protected by the law of 12
July 1973 on nature conservation: they can only be taken in small quantities, but
cannot be marketed. The marsh callitriche is strictly protected by the law on the conservation of nature of July 12, 1973 and any collection in kind is therefore prohibited, except by way of derogation, only for certain reasons of general interest.
ANIMAL COLONIZATION OF THE POND
The pond will very quickly be populated by an impressive number of unicellular organisms (protozoa) and small microscopic invertebrates which will regulate its ecological balance and initiate the food chain. Most of the time, these organisms will be unwittingly brought along with the vegetation; we can even speed up the process by “inseminating” the pond with a few buckets of silt from a nearby wetland. After these representatives of the micro-fauna, many other animals will spontaneously colonize the pond and transform the body of water into an environment teeming with life. Among these, the most numerous will undoubtedly be insects: once installed near the pond, some will stay there the rest of their lives (beetles, aquatic bugs ...) while others will not congregate there. than to lay their eggs (dragonflies, caddisflies, mosquitoes ...). Many insect species thus pass through a larval stage adapted to aquatic life before disseminating to new wetlands, once they become adults. We can therefore see that, unlike the vegetation, the animal colonization of the pond establishes itself fairly quickly. Insofar as any animal introduction risks greatly disturbing the biological balance of the environment and causing a profound upheaval in the life of the pond, animals should not be introduced there.
In particular, care should be taken not to introduce fish into small ponds (surface area less than 25 m²). In fact, they are likely to compete with other animal species because they consume a lot of oxygen; what is more, they are unparalleled predators capable in a short time of wiping out the insect populations of the pond (dragonflies in particular) and completely disrupting the food chain! Worse still, some species have the annoying habit of stirring up the mud, which makes the water cloudy and therefore prevents light from entering the water and disrupts the development of animal and plant life (dieback of plants, oxygen depletion, etc.). If your garden is located in an environment that is favorable to them, the amphibians (frogs, toads and newts) will come by themselves to colonize your pond. This is usually the case if there are other wetlands in the vicinity, i.e. within a radius of 1 or 2 kilometers. Otherwise, there will be a strong temptation to reintroduce tadpoles, frogs and newts yourself. These animals have very specific ecological requirements (need a hunting area and hibernation sites around the pond) and, if these are not met, they will very quickly be doomed to die in a corner of your house. garden! Finally, it should be noted that all amphibians, their larvae (tadpoles) and their eggs are protected by the law on nature conservation and that it is therefore forbidden to collect and transport them. The only exception that could be made to the rule of “no introduction of animal species” concerns water snails (planorbes and limnea). As their low dispersal power prevents them from colonizing newly created environments and as they play a major role in the decomposition of organic matter, it may be interesting to take a few specimens from nature (pond or swamp) and introduce them into the pond.
About the balance of the natural pond ...
All living organisms in a natural pond are subject to the same law: to eat or to be eaten. The result is the constitution of a very complex food chain linking plants to predators, including herbivores, not to mention the decomposers that transform dead organisms into nutrients that can be assimilated by plants. Let us take an example by referring to the illustration on the following page: in the presence of light, carbon dioxide and mineral salts dissolved in water, aquatic plants such as the Ceratophylle grow and multiply. The tadpoles of the common toad, herbivorous in the first weeks of their life, nibble on these aquatic plants. But the dragonfly larva lurks; formidable predator, it will consume many tadpoles to develop. This larva will metamorphose after a few years into an adult dragonfly. This will be caught by a russet which can itself be eaten by a terrestrial superpredator. When he dies, his corpse will be eliminated by the decomposers. These are bacteria that transform the remains of living beings into water, carbon dioxide and mineral salts, that is to say the three compounds essential for the growth of plants. The circle is complete ... and the cycle can start over and over again.
In the natural pond, these cycles work well and a balance between decaying organisms and decomposers is established on its own after some time. However, all external interventions such as the introduction of non-native fish and plants, the installation of an air pump, ... risk unbalancing the ecosystem or causing disturbances. However, these imbalances often result in various nuisances: proliferation
algae, mosquito invasion, bad smells, ...
As long as we let it evolve naturally and we are not too interventionist, a natural pond balances itself and is not a source of any nuisance.
MAINTENANCE OF THE POOL
It's your turn ! What are the animals and plants in the pond?
Maintenance work on a natural pond is not normally very important. However, there are some basic principles to keep in mind to keep the pond healthy. First of all, it will be necessary to take care to limit the quantity of plants which decompose in the pond, in particular the contributions of dead leaves. Care should also be taken NOT to MOW THE TURF TOO FREQUENTLY near the pond as the accumulation of cut grass in the water has a detrimental effect on the life of the pond. Ideally, we can even keep a strip a few meters wide all around the room where the grass will be mowed once or twice a year. In this way, a refuge area will be created for insects and amphibians which, in certain seasons, move away somewhat from the aquatic environment. Then, make sure that the pond does not dry out too much in summer. Indeed, if the tarpaulin is exposed too strongly to the sun's rays, it may suffer and even crack! Excessive losses due to evaporation can therefore be compensated for by a gradual supply of city or cistern water (the temperature of which must be close to that of the water in the pond).
Finally, you should know that, from its creation, THE AQUATIC ENVIRONMENT WILL NOT STOP EVOLVING AND TRANSFORMING. With the help of animal and plant colonization, the pond will very quickly be populated by a host of organisms. Over time, the invasion by aquatic plants may become very important, especially for small ponds. It will be advisable to limit the development of this vegetation if we do not want to witness a progressive filling of the water body (natural phenomenon of eutrophication). In order to be able to detect any problems (see Table 3), it is therefore important to regularly monitor the development of the pond. In this regard, know that a healthy pond is characterized by a balanced development of its fauna as well as by the CLEAR AND TRANSLUCENT character of its water.
In the first months following its creation, any pond created artificially is subject to a risk of imbalance. The latter can be marked by a significant development of floating and submerged plants (algae, duckweed, etc.), often caused by too much nutrient content in the water. Before becoming unnecessarily alarmed, it is above all necessary to be patient: the pond should normally find its own balance with the development of fauna and other aquatic plants. After two or three years, the aquatic vegetation will often tend to gradually invade the whole pond. It will then be important to keep areas of open water to allow sufficient sunshine for the pond. This is why, each autumn, it will be necessary to eliminate some of the submerged plants and floating plants, as well as to mow the plants and the banks (+ export of the mowing product). We can take the opportunity to provide excess aquatic plants to people who have just dug a pond. But beware ! When removing vegetation, certain precautions should be taken so as not to unnecessarily massacre the animals which preferentially take refuge in aquatic plants. Before eliminating the plants, they will be shaken energetically above the pond, then they will be left to rest for a few days in the immediate vicinity of the banks or on a net placed a few centimeters above the water level. In this way, the animals will be able to escape and regain their aquatic habitat on their own. Better still, to leave refuge areas for aquatic life, we will not clean the entire surface of the pond the same day. After a few years of installation, it is possible that the eutrophication process is more marked, which results in a plant invasion, a cloudy water and an increasingly pronounced siltation. Ultimately, we can even witness the biological death of the pond, caused by oxygen depletion of the water. To thwart this process, it will be necessary to drastically limit the development of floating vegetation - which limits the sunshine - and to eliminate part of the mud which tends to accumulate in the bottom of the pond. Finally, if the eutrophication process is really too advanced, we can empty the pond, let it dry for a few days, remove as much mud as possible, while taking care not to make a hole in the tarpaulin, and finally put the pond back under. water. But be careful, drainage should only be practiced in an exceptional way insofar as it strongly disrupts the life of the aquatic environment and afterwards requires the establishment of a new biological balance!
Problems that a newly installed pond may encounter
Pullulation of bacteria,
- milky water
- too much organic matter (plants, animal corpses, ...)
- lack of oxygen following an ecological disaster
- remove the slime
- fill with fresh water
- wait for the action of oxygenating plants
- Water lentils uniform green film on the surface of the water (water too rich in nutrients)
- regularly remove the lenses with a landing net or sieve
- wait for food reserves to drop
- young pond: no predators of mosquito larvae yet
- water rich in nutrients wait for equilibrium to settle
Pullulation of algae, thick interlacing of “threads” of algae around other aquatic plants
- water too rich in nutrients
- bottom of the pond rich in humus
- water very exposed to the sun
- remove the debris accumulated at the bottom
- remove masses of filamentous algae
- promote a natural plant cover of the pond with floating aquatic plants that will limit the sunshine
GOOD TO KNOW
Purchase of tarpaulins and various materials.
Today, getting a tarp is no longer a problem. Most supermarkets (DIY) and other gardening establishments provide it. However, the competition is stiff. Base material (plastic, PVC, butyl rubber ...), thickness of the tarpaulin, width of the bands, texture, number of years of guarantees, are all parameters to be taken into consideration because they vary the prices from simple to triple!
The best solution is to get cuttings from other pond enthusiasts. You can also find a few linen stores selling plants at great prices.