Fresh Water and Aquatic Life

Water, as we have seen, is an essential part of all living matter. So it is not surprising that water should also be an ideal home for living matter itself. Wherever there are rivers, lakes, reservoirs, and ponds, there is some form of life. Well-water may also contain organisms, but in most water deep underground, life is impossible for lack of nutrients, oxygen, or light.

No organism can live without dissolved salts, for it needs these to build up its protoplasm. Plants absorb salts directly from the water, while animals obtain salts by eating either plants or other animals. Since fresh water is usually moving, it has little time to accumulate salts. The sea, on the other hand, has no outlet, and therefore accumulates salts that have been washed down from the land for millions of years. Thus fresh water seldom supports a plant and animal population to anything like the same extent as the sea.

Nevertheless, lakes and rivers do support a considerable number of organisms, mainly in the top 10 to 20 feet, which is the depth to which light penetrates. Here microscopic plants, called phytoplankton, use light for photosynthesis, and provide food for minute animals, which in turn are eaten by larger ones. At the other extreme, fresh water may contain large water plants, which in excess choke lakes and rivers; they may also contain large animals, such as the hippopotamus. In rivers, most of this life occurs in the slow-moving reaches, in deltas, and in coastal plains, where the river nears its end and therefore has the highest concentration of salts. Also, the flow is not as fast as upstream, so there is a better foothold for organisms.

Much of this life in fresh water is harmless, and some is beneficial. But in water there also lurk organisms, invisible to the naked eye, that have caused more sickness and death than all the wars in history. These are the pathogenic bacteria, viruses, and protozoa. We can show the impact of these organisms by taking the city of London as an example, because it was one of the first cities in the 19th century in which a rapidly expanding population led to serious trouble. Between 1831 and 1893, for example, London suffered badly from nation-wide cholera epidemics that claimed 50,000 victims—almost as many civilians as died in Britain during the air raids of World War II.

At the beginning of the 19th century, the expectation of life was only 30 years. This was largely due to the effect of several water-borne diseases, such as typhoid, cholera, dysentery , virus jaundice, and gastro-enteritis. It took a long time for people to realize that the cause of these diseases was bad sanitation and infected water. Very few people had water closets, and human waste was discharged into ditches and cesspools. This was quite a good method of sewage disposal for small villages, but was not suitable for large cities like London, which drew much of its water from wells. When large amounts of sewage seeped through the ground, the pathogenic bacteria in it sometimes leaked through cracks in wells to infect the water. Thus one infected person spread disease to hundreds of others.

Up to 1815 it was a penal offence to discharge human waste into the River Thames, then the main source of domestic water. But as water closets became more common, a. network of sewers was built, which inevitably ran downhill to the river. Rivers can cope with small amounts of sewage, but the large quantity of sewage that now poured into the Thames meant that London’s main water source became dangerous to health, in addition to the already contaminated wells. People continued for some time to take water from the tidal reaches of the Thames, often from near sewer outlets, so that the old complaints persisted, especially during hot weather when bacteria thrive best. Ironically, the efforts to improve sanitation, and thus health, by providing extensive sewers defeated its own purpose.

In 1852 the first real move to improve the water supply was made in London by the passing of the Metropolis Water Act. Water companies were obliged to remove their river intakes out. of the tidal zone of the Thames, to above the first lock at Teddington, and therefore out of reach of London’s sewage. The Act also ordered the filtration of all river-derived water. The engineer James Simpson had introduced an experimental slow sand filter at Chelsea in 1829, and the subsequent fall in the cholera rate in this area proved it a great success; yet filtration did not become common until after 1866. Meanwhile, Dr. John Snow showed by careful observation that many diseases were not air- borne, as was generally believed, but water-borne. Then came the discovery of bacteria, and the story of water-borne disease was nearly complete. In 1885, the Water Board of London began a routine bacteriological check of all river water, but many years elapsed before bacteriological checks were kept on all rivers.

In spite of filtration, and siting the water intakes at less polluted parts of the river, water-borne disease persisted until the early 1900s. Various improvements took time, but did not keep pace with the rapidly increasing population. The advent of safe water only came with the widespread application of chlorination in the 1930s . Not only do minute amounts of chlorine destroy up to 99.95 per cent of all intestinal bacteria; it can be added to water just before it enters the mains. So whatever pathogens may have survived filtration are destroyed in the end. During this century, there have been sporadic outbreaks of typhoid due to the lack of chlorination, and water authorities finally realized that the process must never be omitted.

In order to eradicate disease, water must not only be sterile, but should be supplied to every house in sufficient quantity. Up to the middle 1800s, few of the houses in large cities had a piped water supply, and then only for a few hours each week. The poor often begged water from the rich, and stored it in vessels, where it was liable to contamination. But when houses began to receive piped water, people were able to wash themselves regularly as well as their clothes and premises, thus removing disease-producing parasites such as lice. More important still, people began to wash their hands, so that intestinal pathogens were prevented from spreading to food and other people by contact.

In many under-developed countries, the prevalence of water-borne disease is still as it was in England 100 years ago. In some of these countries, intestinal disease is still one of the prime causes of infant mortality, and as there is no efficient chemotherapy, the only answer is a safe water supply. But it is very difficult to convince people of the benefits of hygiene, especially where water is concerned; and even when they are convinced, they do not always have the capital to install a safe water supply.

There are many diseases in hot climates that are not caused by bad sanitation, but are simply due to the presence of water. Canals, marshes, cisterns, water butts, and holes in trees, all provide breeding places for the young stages of mosquitoes that transmit malaria, yellow fever, and dengue fever. Water also supports several worms and flukes that infect men and cattle. Of particular importance is the fluke Bilharzia , which in the tropics and sub-tropics causes great suffering to over 130 million people. When a person comes in contact with infected water, the parasite enters the skin and breeds inside the body. The eggs pass back into the water with the excreta, and the offspring then become parasitic on snails, from which hundreds of new parasites later emerge to infect more people. In many areas, irrigation has led to a sharp rise in this disease, largely defeating efforts to improve health by increased food production. In Egypt and the Sudan, irrigation from storing the Nile floodwater increased bilharziasis to a level where, in some areas, 80 per cent of the population were infected.

Some countries are beginning to learn that water projects must be designed to prevent parasites from becoming established, or be prepared for the large cost of killing them by the continual application of selective poisons. At present, the health of a large proportion of the population in many tropical areas is so undermined that their low production and standards of living are hardly surprising. Thus in some parts of Africa, 10 debilitated natives are needed to do the work of one healthy European; the natives are not necessarily idle, but simply miserable and weakened by parasites.

We now move on to the forms of life that do not cause disease but instead give trouble to water authorities. Problems begin as soon as water enters the storage reservoir. Although many bacteria die in static water, it is an ideal habitat for algae. At certain times of the year, algae may reproduce explosively, especially when polluted river water charges the reservoirs with nutrient salts. Algae then block the reservoir filters or slow sand filter beds, so that it is difficult to maintain the flow. Some algae also impart to water a taste that is sometimes difficult to remove; others produce substances that are inoffensive except in certain industries, such as those producing soft drinks.

Even after water has left the waterworks it may be contaminated by other forms of life that establish themselves in the mains. In the past these organisms were quite a problem: in 1886, for example, the pipe network in Hamburg became blocked with eels, sponges, shrimps, water lice, and worms, which although harmless enough were unsavoury things to emerge from the domestic tap. Today, filtration is always practised in efficient waterworks, so that the presence of large organisms in the mains is rare, but this is not so for micro-organisms. However efficient the filtration, some dissolved organic matter may well enter the mains to provide food for these micro-organisms; if the water also contains dissolved iron salts, brownish slimes are produced by iron bacteria, which on decay may give water an unpleasant colour and taste. Iron bacteria also cause nodular encrustations of rust inside pipes, reducing the water flow by as much as 75 per cent, and providing pockets that may harbour larger organisms.

During the last 50 years, water-weeds have gained a strong foothold in many parts of the world. The most troublesome weeds are those that become established in countries far away from their native haunt. One way in which this happens is when foreign aquarium plants are imported with tropical fish and are then emptied into streams. Rooted weeds establish themselves in the slow-moving parts of rivers, impede the current, and therefore cause more silt to accumulate around their stems, providing anchorage for new weeds. The main offenders are the floating weeds, especially the South American water hyacinth. In only four months, a couple of parent plants multiply to over a thousand, creating vast, interlocked mats a metre thick.

In 1890 several southern states of North America were infested, by 1895 Australia, India by 1902, and 1000 miles of the river Congo by 1952. By 1960, 600 miles of the White Nile were covered, as far as the Jebel Awlia Dam near Khartoum. Navigation almost came to a stop, for the White Nile is the only means of communication through southern Sudan. Irrigation pumps were blocked, and fishermen were unable to wade for fish, many of which had already died through deoxygenation of the water. Furthermore, the large amount of water lost by plant transpiration only made matters worse in an area where already half the original Nile flow is lost by evaporation.

Complete eradication of the water hyacinth is unlikely, for the seeds can lie dormant for several years, and are very resistant. With sufficient money, it is possible to control the plant, as practised in the southern states of North America, but money on a large scale is seldom available for underdeveloped countries. At the Jebel Awlia Dam, for instance, £500,000 are spent annually in just keeping part of the White Nile navigable and in preventing fragments of the plant from passing downstream, where there is a danger of obstructing the irrigation canals near Khartoum and the canals of the Gezira cotton plantations. Dragging the mats out of the water is extremely difficult and expensive; so is spraying with herbicides such as 2,4-D. Aerial spraying, which is often the most economical method, is not always feasible, because crops such as cotton are particularly susceptible to 2,4-D. At the moment the possibility of biological control is being examined, but as yet this has not been successful.

Another troublesome floating plant is the water fern. Also a native of South America, the plant has spread to several parts of the world, where it often interferes with irrigation schemes. Over a period of 12 years, the plant has covered 22,000 acres of Ceylon’s rice fields. In 1962, 400 square miles of Lake Kariba were covered, creating a mat that was so dense that it provided anchorage for as many as 40 different rooted plants. Now only 10 per cent of the lake is covered, and fortunately the prevailing winds drift the mats away from the grids of the turbine intakes at the Kariba Dam.

Not all fresh-water organisms, however, are detrimental. Some are invaluable, especially in the yearly disposal of hundreds of thousands of tons of sewage. If this waste accumulated, there would be a very high disease rate, quite apart from its offensiveness. As it is, micro-organisms find in sewage a rich source of nutrients and energy, and break it down into harmless substances. This natural process of purification occurs in rivers, lakes, and in the soil; microorganisms are also used in sewage works and to treat industrial organic waste.

Micro-organisms are also sometimes used for treating domestic water, in combination with slow sand filter beds . Although this old method has been largely superseded by chemical techniques, slow sand filtration still remains an efficient method for some water undertakings. After filtration has proceeded for some time, a jelly-like film appears on the surface of the sand, formed by bacteria and algae; these are followed later by bacteria below the surface that surround each sand particle with a similar film. Both these films form an extremely efficient filter for small suspended solids and bacteria. But the action is more than a straining process: the organisms also oxidize organic matter to inorganic compounds, precipitate iron salts, and retain the copper salts that are used to destroy algae in storage reservoirs. Also, the algae oxygenate the water, hastening the oxidation of harmful substances and preventing anaerobic bacteria from flourishing deep down in the filter bed.

Finally, there are the fish that spend part or all of their lives in fresh water. For people who cannot obtain enough protein from meat and dairy produce, such as those living near the large African lakes, fish may be often the only source. In the Far East, fish are farmed in tanks, and also in flooded paddy fields. In affluent countries, fresh-water fish are not so important as a source of protein, but salmon and trout are still luxury dishes. These edible fish, and many others, have disappeared from many rivers because of pollution, which either deprives the water of oxygen, or directly poisons the fish. Open-air recreations, however, such as fishing, are becoming ever more important as man seeks to escape from the mechanization of city life. It is therefore a moral responsibility that lies with local authorities and industry to do everything in their power to prevent the pollution of rivers.

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