POND PLANTS

If a pond is to be a successful habitat it must have plants growing in it. They provide food, oxygen and shelter for the animals. Green plants need sunlight to make their food (photosynthesis) so a pond in the open will be more successful than one in the shade. The smallest plants in a pond are the microscopic phytoplankton and these provide most of the food in a pond. The phytoplankton and larger algae form the first part of the pond’s food chains. Plant-eating animals – the herbivores – eat the plants and the herbivores are eaten by carnivores (meat eating animals).

Pond vegetation grows in areas called zones. Plants such as great willowherb and meadowsweet grow in the bankside zone: they like damp places but are not true water plants. The emergent plants grow nearest to the pond edge in the marsh zone e.g. yellow iris and mud-sedge. These fringing plants provide good hiding places for some pond animals such as young frogs, and the tall stems are used by dragonfly nymphs when they climb out of the water before emerging as an adult.

In the aquatic zone live the truly aquatic plants. Some of them float on the surface with tiny roots dangling in the water e.g. duckweed and frogbit. Others have their roots buried in the mud at the bottom of the pond and their leaves float on the surface e.g. water-lilies and crowfoot.

Then there are fully submerged plants such as starwort and Canadian pondweed. These produce most of the oxygen so it is important that they receive plenty of sunlight (oxygen is produced during photosynthesis). If the plants on the surface are completely covering the pond then some of them should be pulled out or the submerged plants will suffer.

Some species of pond plants, such as the water-violet, are becoming very rare indeed.

Even the smallest pond will have a population of amphibians (frogs, toads and newts), small fish e.g. sticklebacks, and a huge variety of invertebrates (minibeasts). Some of these are herbivores such as water fleas and snails, whereas others are aggressive carnivores, hunting down their prey, the unfortunate herbivores! One of the largest invertebrate predators in a pond is the great diving beetle – no tadpole is safe when one of these hunters is around!

Many different food chains are to be found in a pond because each animal eats different things.

ENDANGERED POND ANIMALS

As with any habitat, if ponds are in danger of disappearing then it follows that the wildlife in them is also endangered. Some pond animals are already officially on the list of rare animals, fully protected by the Wildlife and Countryside Act 1981. The great-crested newt and natterjack toad are the two officially endangered species of amphibian but even the common frog is not nearly so common as it used to be. The many species of dragonflies are also becoming increasingly rare – the Norfolk Aeshna is on the list of Britain’s endangered species of insects.

POLLUTION OF PONDS

The water in a pond must remain clean if it is to provide a healthy environment for the organisms (animals and plants) living in it. The natural waste from the living and dead organisms is ‘recycled’ by special tiny organisms called bacteria. Plenty of oxygen is needed for the bacteria to ‘break down’ the waste. The pond can take care of its own waste – it’s people who cause pollution!

The most noticeable kind of pollution is the dumping of rubbish – anything from old cars and cans to bikes and bottles have been found cluttering up ponds. Such thoughtless behaviour not only makes the environment look so unsightly but it may also destroy pond-life.

Perhaps the most serious threat to ponds is chemical pollution as a result of modern farming methods. Over the years fields have been sprayed with pesticides to rid the crops of pests. However, rain often washes the excess chemicals off the crops into nearby ponds, streams or rivers, poisoning some of the animals living there. Fortunately, these poisonous chemicals are not used so freely now and, hopefully, this problem will gradually be reduced.

Another, equally serious, problem connected with agriculture is the use of artificial fertilisers. Powdery chemical fertilisers, containing nitrates, are put on the crops to help their growth but they can also be washed off by rain into nearby ponds. They do not poison the wildlife but the rich supply of nitrogen causes the water plants, especially algae, to grow very quickly. The plants use up so much oxygen during the night and when they decay that there is none left for the other pond-life. The growth also prevents sunlight reaching the organisms below. Eventually, all the algae die leaving a stinking, decaying mass. The case of excess nitrates in water is called eutrophication.