Ponds – A multipurpose habitat

Geetha Iyer

The word ‘pond’ probably arose as a variant of the word ‘pound’ which means ‘an enclosed space’. Scientists have yet to agree on a conclusive definition of a pond. One definition is that it is an “artificially banked body of water”. It is interesting to note the use of the word ‘bank’ in defining a pond. The way the earth’s fresh water bodies are being raped, water might well become a currency tool, and the pond, naturally then, a kind of bank. An interesting thought!

Ponds are a familiar structure to all and need no introduction. But their familiarity is also a reason for their destruction. People take them for granted. How they do is the sad story of water pollution.

Types of ponds
Ponds come in all shapes and sizes. Any depression on the ground will collect water and a pond is born. Thus they may be naturally formed or artificially constructed. Naturally formed ponds are generally seen in floodplains and arise as a result of natural processes. These could be due to geological or ecological events. Craters formed by asteroid hits have become ponds and lakes. Melting glaciers often cause small depressions – potholes – that get filled with water. Excessive sand mining in river beds leave potholes, landslides with giant rocks hitting the soil leave permanent depressions, abandoned quarries, all of which are prime candidates to form ponds as rain water fills in. Temporary ponds are formed when depressions in soil occur due to weathering, which then get filled with water during monsoons.

Artificial ponds are constructed by humans beings. This is an activity that has been going on for centuries. From time immemorial they have been used by civilizations, ancient and modern, for food sources or private use, as an indicator of wealth, for religious events and a source of spirituality. There are many historically significant ponds. But the focus here is about ponds as part of a wetland system and their importance in conserving biodiversity.

Although ponds are constructed for economic activities, there are many that were built by erstwhile rulers primarily to conserve water and recharge the groundwater system. They soon became repositories of biodiversity. As plants and animals came to occupy them, the idea of using them for other activities took shape. This was probably the first step to their pollution and decline. The best example probably is the case of ponds being used to cultivate lotus and fish, useful in many ways and yet polluting because of human intervention.

Lotus ponds are present all over our country. In fact, some lotus ponds are so large that they should probably be referred to as lotus lakes. As many large enclosed waterbodies continue to be called ponds, there is no consensus over the definition of a pond.

Lotus¹ ponds were quite abundant till a decade ago. Not anymore; their disappearance is part of the ongoing events that cause destruction of wetlands. Lotus has a near universal appeal and presence in Asian countries, especially Southeast Asia. The economic value of this pond is many faceted. All parts of the lotus are useful. The leaves are excellent wrapping material. Flowers, fruits and garlands were traditionally wrapped in lotus leaves and sold as they remain fresh and don’t wither easily. Lotus stems are edible and are rich in vitamin C. They are also rich in potassium and need to be avoided by those with heart or kidney ailments. Besides their nutritional value, stems, leaves and seeds are used in preparation of medicines offering relief for a variety of ailments.

Grown from seeds, it’s not too difficult to cultivate them. However, they blossom well if the ponds have some depth. Lotus ponds are a common feature around temples and monasteries. A variety of birds, fish and insects inhabit these ponds. Two bird species that have specially adapted to live in lotus ponds are the Jacanas. Both the bronze-winged and the pheasant-tailed jacanas live and breed in these ponds. Their feet are adapted to walk and run over the leaves. Along with these, one can also see cormorants, egrets, pond herons and kingfishers. Sometimes dabchicks and coots also swim in. Aquatic snakes such as the olivaceouskeel back can be spotted. Dragonflies and damselflies are quite common as the slushy bottoms of the pond offer the right kind of habitat for the dragonfly larvae. Other aquatic breeding insects such as caddisflies, stoneflies and the ephemeral mayflies too may be found associated with these ponds. The typical example of food chain (Insects-fish-bird or Insects-frogs-snakes) that children learn is one common to ponds. Last but not the least, lotus ponds are used by several cultures for spiritual reasons. Lilly ponds are often mistaken for lotus. Lotus and lilies are two distinctly different species. Lilly ponds too can sustain biodiversity.

Fish ponds
These are as common as the lotus ponds. They may be naturally occurring, maintained for harvesting fishes or artificially created for meeting commercial needs. Ponds in eastern India are typically homestead ponds of less than 1 ha in size, whereas in western India they are much larger reaching an expanse of 15-20 hectares. Sixty per cent of Indians consume fish, hence fish ponds and fish farming are attractive means for income generation. Fish ponds are also built to rear ornamental fish for sale to aquariums. Many of the fish one finds in the aquaria were once upon a time naturally occurring ones. For eg: guppies are a great favourite with aquarists. They come in beautiful forms and colours that have not always developed naturally. Years of careful breeding has resulted in the forms that are sold today. Similar is the case with other aquarium fish such as mollies, fighters, zebras, angels, etc.

Multipurpose ponds and biodiversity
In many states, ponds or tanks as they are locally referred to are, in fact, farm ponds. They are formed and sustained by rain water. These farm ponds are used for meeting agricultural or horticultural needs as well as for farming fish. Those who breed ducks and geese also use these ponds. Several such ponds in Kanyakumari district serve multiple purposes. They are used to water paddy, for raising fish, grazing ducks and geese and growing lotus.

Some of these multipurpose ponds that attract migratory birds have been declared as Important Bird Area (IBA) by Birdlife International, an organization involved in conservation of birds. Found in these ponds are also several aquatic insects and a diverse population of invertebrates that serve as food for birds and fishes. The web of life in ponds keeps it healthy if human beings avoid using it for personal use, especially washing clothes. Detergents used to wash clothes result in algal blooms that can lead to the death of aquatic life.

Lotus cultivation on a commercial scale involves large scale use of chemical fertilizers in water leading to pollution. A large number of birds during migratory season breed in these waters and pollution affects their breeding process. Commercial farming of fish in such ponds are resulting in the decline of native species. Just as hybrid varieties of rice and wheat seeds have led to the loss of native varieties, a similar scenario exists in the cultivation of fish. Exotic and fast breeding varieties of fish are being introduced into these ponds. Native fishes often find it difficult to compete with the exotic ones and soon die. Gene banks for conserving the gene pools of native fish varieties are now being established in a few places.

Activity – Inventory of biodiversity in ponds. Ponds are aquatic habitats, hence fish would be the organism that you would automatically name if asked about the biodiversity in ponds. But ponds are host to a wide variety of organisms. They are fresh water habitats, except for those ponds that may be formed near coastal or estuarine habitats. While vertebrates such as fish, birds and mammals are visible easily, there are several invertebrate populations thriving well in them. Among invertebrates there are both macro and microorganisms that can be seen.

An inventory of organisms that are found in ponds would be an activity suitable for middle school science or a project for secondary school science/environment science classes.

Select a pond that is closest to the school. Some ponds, especially lotus ponds can be quite deep. So exercise caution while taking students out to observe.

If a lotus pond or any other pond is nearby then you may make arrangements to take students out in the morning around 7 am. This is the time people come to harvest the lotus or use the pond. It is also the time when birds would be active. You will notice that initially insects many not be visible but as the sunlight begins to warm up the environment, plenty of insects will begin to arrive. Dragonflies gliding over water and butterflies at the periphery of ponds cannot be missed.

Carry a bottle and a small net. A large tea-stainer would also serve the purpose. If you gently lay the net in the water surface allowing water to accumulate in the net, and leave it there for some time, you would see aquatic insects, insect larva, beetles, bugs, mosquitoes, and small fish or fish fry swimming into the net. Daphnia or water fleas, hydra are some of the common invertebrates seen in ponds. If you scoop up some soil from the edge of the pond, then worms and snails can be seen. Some ponds may have leeches in them.

An interesting insect seen in ponds are the water striders. These are bugs with long legs that use the surface tension of water for their movement.

Observe also human activities around the pond. Are people using the pond to bathe or wash clothes? Observe if people use the pond to clean their vehicles? Are the lotus (if present) being collected?

Collect some water and take it to your class.² Place a drop of the pond water in a glass slide and observe under the microscope. You are likely to see different kinds of protozoa such as paramecium. The links (2 & 3) given in the reference section give you details about setting up a microscope and slides to see microorganisms from a pond, as well as videos³ of these organisms.

Discussion questions
Once you have completed the inventory of the biodiversity⁴ of pond life, explore how many different food chains the pond life supports. Create a food web. Discuss the role of each organism in relation to the pond.

What were some notable features of the ponds that you observed? Was it a pond formed by water from rains? Would it dry if the monsoon failed? What is likely to happen if the pond dried up?

Ponds in stress and on the decline
Despite the economic, cultural and spiritual benefits the ponds provide, many of them are on the decline. Eutrophication is increasingly becoming a common phenomena.⁵ Land needed for housing and industries often target dry ponds. Lotus cultivators use plenty of chemical fertilizers which affect the water quality and the organisms living in there. Similarly, intense aquaculture in ponds create stress in the aquatic system and affects biodiversity. Many ponds in rural areas are used for bathing and washing clothes. Excessive use of detergents have led to increased algal growth and a decline in aquatic life. In some remote areas such as in Rajasthan, ponds are the only source of drinking water for rural populations. If they are not maintained then the health of the rural populace gets affected.

Ponds are stagnant water bodies. The earlier rulers who constructed them took care to create entrances and exits so that stagnant water in the pond would be naturally drained during rainy seasons and replenished. This would ensure that algal growth are kept in check. However, such systems are slowly being destroyed due to construction activities that block exits and so water stagnation and algal blooms destroy the health of ponds.

Those who are water starved understand the significance of ponds and build new ones to store rain water and recharge ground water. But for those who are used to piped water, the importance of ponds is hardly understood. We need ponds for food, to recharge ground water and for sustaining biodiversity.

Pond builders can be seen in the animal world too. Beavers construct them, as do alligators, occasionally excavating the soil for their very own private pool! And they keep them healthy. A lesson there for humans. Private ponds- pools, it would seem, are not the invention of humans but polluting them sure is.

References

1. Lotus: https://agricare.kisanhelp.in/content/lotus-cultivation-potential-field-earning
2. http://www.biologyeducation.net/classroom/the-hidden-world-of-microorganisms-1/
3. https://www.microscopyu.com/galleries/dic-phase-contrast/pond-life
4. https://people.wou.edu/~bledsoek/pond_organisms/pond_organisms_2.htm
5. Housing project a threat to Suchindrum – Theroor Pond-IBA site. https://www.thehindu.com/news/national/tamil-nadu/housing-projects-pose-threat-to-suchindram-theroor-bird-sanctuary-in-tamil-nadus-kanniyakumari-district/article32767615.ece

The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.