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 drinks cans to bikes and bottles have been found cluttering up ponds. This 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 during decaying processes 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 smelly, decaying mass. The case of excess nitrates in water is called eutrophication.
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