Rivers are a clear example of surface water. They are defined as the natural current of water flowing through a bed from a high place to a lower place. The vast majority of rivers flow into the sea or a lake, although some disappear because their water seeps into the land or evaporates into the atmosphere.
They are an important source of water supply for agricultural and domestic uses. But, in recent years, the rivers have been affected by the negative effects of pollution.
The amount of water flowing in a river, flow, varies over time and space. These variations define the hydrological regime of a watercourse. Temporal variations occur during or just after storms, the runoff produced by the river increases the flow. In extreme cases, flooding can occur when the supply of water exceeds the capacity of the river to discharge it, overflowing and covering flat areas or nearby floodplains.
Water that travels underground, such as furrowed streams or groundwater, takes much longer to feed the river flow and can reach the river days, weeks or months after the rain that generated the runoff . Also, the flow of a river provided by groundwater is called base flow, which fluctuates with the height of the water table.
If there is no rain at all or if the average precipitation is below normal for long periods, the river can dry up as the inflow of rainwater accumulated in the ground and sub- ground reduces the base rate to zero. This can have disastrous consequences for life in the river and its banks and for the people who depend on it for their water supply.
The spatial variation occurs because the flow of the river increases downstream, as waters from the watershed and contributions from the basins of other rivers that join it as tributaries are collected. For this reason, the river is generally small in the mountains near its source, and much larger in the lowlands near its mouth. The exception is in deserts, where the amount of water lost to the atmosphere by seepage or evaporation exceeds the amount brought in by surface currents. For example, the flow of the Nile, which is the longest river in the world, decreases dramatically as it descends from the mountains of Sudan and Ethiopia through the deserts of Nubia and the Sahara to the Mediterranean Sea.
The quantity, variations and regularity of the waters of a river are of capital importance for the plants, animals and men who live along its course. Rivers and their floodplains support diverse and valuable ecosystems, not only because of the vital capacity of fresh water, but also because of the abundance of plants and insects it supports and which form the basis food chains. In the riverbed, fish feed on plants, and insects are food for birds, amphibians, reptiles and mammals. Outside the channel, wetlands produced by seepage and flooding support rich and varied environments, not only important for native species, but also for migrating birds and animals that use the wetlands as passageways during their migrations. seasonal. River ecosystems, also known as fluvial ecosystems, can be considered a group belonging to the most important in nature and their existence depends entirely on their regime. Care must therefore be taken not to modify this regime when acting on the river and its basin, because irresponsible management of water resources or their overexploitation can have disastrous effects for the riparian ecosystem.
The use of rivers And the conflict between nature and the exploitation of river resources is not new. Rivers and their floodplains, estuaries and deltas have played a central role in history, influencing agriculture, transport, industry, waste dumping and human settlements. In fact, the Tigris and Euphrates rivers in present-day Iraq made Mesopotamia, which literally means “between the rivers”, the cradle of civilization around the second half of the 4th millennium BC. The long historical association between society and rivers is evident. because of their great strategic, commercial and religious importance. For example, the Ganges in India is sacred to Hindus, who visit it to purify themselves by bathing in its waters.
Initially, rivers attracted people because of the security they offered in water supply and the rich agricultural soils they provided. Along the river, one could travel and explore new regions or transport bulky goods over long distances without the need to build roads through difficult terrain or thick vegetation. Later, it contributed to the early days of the Industrial Revolution by providing both an important raw material and a source of energy to power water wheels. Many industries still exist along the rivers, although they no longer use this hydropower for commercial purposes.
In many cases, rivers have been used as sinks for agricultural and industrial waste. Thanks to their current and ecological nature, the rivers are able to regenerate themselves by admitting dizzying amounts of tributaries. However, all rivers have a limited capacity to assimilate wastewater and fertilizers from agricultural land. If this limit is exceeded, the proliferation of bacteria, algae and plants will consume all the oxygen dissolved in the water, eutrophication, which leads to the destruction of the entire river ecosystem because the trophic chains are interrupted.
Contamination of water by chemicals that are not usually present in the system can have dire consequences, as rivers are highly vulnerable to poisoning by toxic products generated by mining, smelting and smelting. industry, such as heavy metals: lead, zinc, cadmium. .., acids, solvents, etc.
Not only do these chemicals destroy life as the pollution occurs, but they also slowly accumulate in the sediments and soils of the floodplain. The mutations and sterility they cause in animals by eating the vegetation that grows on these lands, in which pollutants are concentrated, can lead to the irreversible destruction of entire natural communities and the permanent degradation of landscapes.
Human beings and animals are not exempt from the dangers that derive from the direct consumption of water or food from these contaminated rivers and soils. The public health problems that can arise are real, even if they have not been sufficiently studied.
Most rivers in industrialized countries are more or less polluted. Tomorrow’s society will not only have to take up the challenge of reducing the current inputs of pollutants, but it will also have to rebuild the natural ecology of these rivers. You will need to clean soils and sediments of chemicals that contaminate them to make drinking water safe.
In developing countries, the challenge is not to repeat the mistakes made by industrialized nations and to prevent the pollution of their pristine rivers and ecosystems. The rivers of these countries, as in the case of the Amazon in South America, are the last refuge of many animal and plant species and the water supply they can provide is the best hope for the sustainable development of many nations.
The importance of rivers transcends national boundaries and local interests. Thus, for its conservation and management, a balanced approach is necessary between developing and developed countries, in order to equitably distribute the costs of its conservation between the two thanks to the recognition of rivers as a global natural resource.
In the article of this section: Rivers and lakes of the world you will find more interesting information.
Wastewater treatment group. Polytechnic University School. University of Seville.
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