Water Exploitation and Pollution
Water Circulation and Its Importance
The existence of water on planet Earth and its circulation are closely related to atmospheric processes. The ocean is a giant reservoir for heat, acquired from solar radiation and released to the atmosphere with delays of several months to decades. The movement of water masses of different temperatures is one of the driving wheels of the climate machine. The proximity to the ocean also has a pronounced effect on local climates (oceanic and continental climates). In addition, the hydrosphere includes groundwater and water in glaciers, in soil, rivers and lakes as well as water in the form of atmospheric vapour. Besides its cardinal function on the global scale, water is also important for individual organisms. It is the primary building material of living bodies. Normally, organisms contain about 60% of water; some, up to 99%.
On this planet, water is virtually never found in its pure state. It always contains some admixtures and dissolved chemical compounds.
As a result of human activity, water contains other substances beyond the natural admixtures or its content of otherwise natural substances is increased unproportionally. The most common causes of water contamination include soil soaking, industrial wastewater discharge, and tank accidents involving hazardous liquids. Polluted water has adverse effects on human health and on the composition and vitality of organic communities. Toxic substances contained in water do not always cause acute intoxication in humans. Instead, they may cumulate in plant and animal bodies and increase their concentrations on their way up the food chain before they reach humans. The consequences may be much delayed (Minamata disease). What is more, many contagious diseases and parasites are diffused through water. Wells are still the sources of typhoid and cholera contagion in some developing countries.
Some waters suffer from excessive content of nutrients – substances essential to plant growth. These include mainly soluble salts – nitrates and phosphates – which come into existence as by-products of organic matter decomposing and are part of agricultural fertilisers. These substances enter the waters via wash-off from fields and pastures. Sewage water from human settlements is also a major contributor of phosphorus and nitrogen-containing substances. Phosphates originate from cesspools and dung, also detergents are a significant source of phosphorus. The process through which water is fortified with excessive nutrients is termed eutrophication. Waters overly rich in nutrients are characterised by progressively increasing consumption of oxygen, needed both by the organisms to breathe and by the bacteria to decompose the dying bodies of those organisms. Such contaminated waters develop anaerobic (zero-oxygen) conditions, leading to reduced aquatic life. Excessive amounts of otherwise necessary nutrients may thus cause a collapse of pre-existing ecosystems due to oxygen insufficiency.
Effect on Water Regime
Human activity need not always cause water pollution. Inappropriate interference with the natural aquatic regime, too, may have numerous negative impacts. Draining of wetlands is unnatural. Straightening of rivers and streams not only reduces their self-cleaning capacity but also enables rapid drainage of the country, resulting in water insufficiency. Filling up of oxbow lakes reduces wild species diversity. Soil amelioration has resulted, among other things, in the draining of large, especially foothill areas. Meadows and forests have lost their retention capacity, and heavy rains trigger floods. Rapid draining of a territory implies reduced water supply for underground reservoirs. Watercourses are fragmented with dams and weirs.
Moreover, excessive irrigation of agricultural land leads to increased evaporation and thus water losses. The textbook example of environmental disasters caused by such interventions was the diversion of the waters of the Amu Darya and the Syr Darya rivers from their original beds, discharging into the Aral Sea, for use in cottonbush irrigation in plantations inside the Kara Kum desert. This has resulted in the drying up of the Aral Sea as well as salinisation of the plantation soil. The construction of Aswan Dam on the Nile was probably another such human error. Admittedly, it has reduced the floods, but with them it has reduced the supplies of the fertile mud, which used to guarantee downstream farmers regular harvests. However, the eroded soil from the upper reaches has been silting up the reservoir; its complete silting is expected, resulting in a shutdown.
The ocean is the largest store of water. More than 97% of all water is saltwater and belongs to the world ocean. This water is thus unsuitable for drinking or irrigation or many other possible uses. Theoretically, immense amounts of freshwater are available underground and in glaciers, lakes and rivers. However, not all this water is within reach and technically exploitable. The amount which the circulation allows us to reuse continually is virtually only that part which returns from land to the oceans annually – in fact a ‘tiny’ fragment of about 40,000 km3 of water per year. This amount is called the stable annual runoff. Not all of this water, however, is usable for plants, animals and humans. Most of it runs off in the form of torrential waters after heavy rains (26,000 km3); more runs down rivers and streams from uninhabited areas (5,000 km3). This means that humans can ‘only’ dispose of about 9,000 km3 annually. Assuming that the global average annual consumption is between 7,000 and 8,000 m3 per capita, the world’s entire population consumes some 3,000-4,000 km3 of water a year, which is less than a half of the water available for human use, about one tenth of the stable runoff, and a mere fragment of what is contained in the large-scale reservoirs, such as the underground or glaciers. Theoretically, there is water galore for us to use.
However, there is a catch: neither precipitation, nor rates of evaporation, groundwater reserves and runoff are distributed evenly across the globe. This uneven supply is the main cause of the concern about lack of drinking and utility water for human use. For example, each Canadian citizen is free to use more than 120,000 m3 a year thanks to the high precipitation; a citizen of Malta, on the contrary, has no more than 70 m3 a year available on the average. People live in even less favourable conditions in many parts of the world. Droughts may drag on for years in some places; other areas are frequently flooded due to high precipitation. In countries with rapidly growing populations, where water sources are scarce, the availability of both drinking and utility water per capita decreases with the multiplying population. It is worth mentioning that this is not only water for drinking, but mainly for irrigation, thus for food production. Globally, 50-80% of all water used goes into irrigation.
Population growth in certain areas of the planet is not the only factor to affect the future availability of drinking and utility water in those areas, which are even now well below the global average in water consumption. Water consumption does not depend on the population count only, but largely on the way of life. Industrial water consumption and its usage in improved household hygiene will increase with growing industrial production (which many developing countries envisage – see Changing Consumption Patterns). Judging the situation soberly, there is often no way out of the problem. The growing populations, particularly in the arid East and Sub-Saharan Africa, will suffer shortages of water both for personal use and for industry and irrigation.