The Role of Rivers in the Water Cycle

The water cycle begins when water evaporates from the oceans into the atmosphere. Atmospheric water returns to Earth as precipitation in the form of rain, hail, or snow. Generally, highlands receive more precipitation than lowlands, and it is in the mountains that most rivers originate. The precipitation on reaching the ground usually seeps into the soil percolating down to the water-table to become groundwater or flowing slowly downhill as through-flow. However, where human activities have compacted the soil surface or covered it with concrete, or where the soil is already saturated, not all the water is able to infiltrate and the excess collects on the surface before flowing downhill to the nearest stream as overland flow.

Water that reaches the river either by through-flow or overland flow is termed run-off. The role of the river in the water cycle is to complete the cycle by collecting run-off from the surrounding area and carrying it back to the ocean or a lake in order to replace water that has evaporated.

The Role of Rivers in the Food Chain

The water flow in rivers has enormous significance for plants, animals, and people living along the course of the river. Rivers and their flood plains possess diverse and valuable ecosystems. Not only is the availability of fresh water in itself vital to sustaining life, but it also supports lush vegetation and abundant insect life that form the base of the food chain.

In the river channel fish feed on the plants and insects and are themselves eaten by birds, amphibians, reptiles, and mammals.

Rich and diverse habitats that are important not only for resident species, but also for migrating birds and animals are formed in the wetlands maintained by seepage and occasionally flooded by the river support.

The Historical Importance of Rivers

Historically, rivers along with their flood plains, estuaries, and deltas have been central to human development involving agriculture, transport, industry, waste disposal, and settlement. In fact, the Tigris and Euphrates rivers in modern-day Iraq provided the cradle for the dawn of civilization in Mesopotamia (literally, “between two rivers”) over 4,000 years ago. The long historical association of society and rivers is also evident in their mystical and religious significance. River Ganges is sacred to Hindus, who visit the river to bathe in it to be spiritually purified.

The human beings were attracted to rivers initially, by the reliable supply of water and the rich agricultural soils laid down by fluvial deposition. Other very attractive opportunities provided by the river were the ability to travel and explore new regions and move bulky produce over long distances without having to build roads through tough terrain or thick vegetation. The river water also supported early industrial development by:

1. providing an important raw material, and
2. being a source of power when harnessed by a water wheel.

Many industries remain centered on rivers even though water-power is no longer used commercially.

The Exploitation of Rivers

Conflict between natural and human exploitation of rivers is, of course, nothing new. Man, for his need has long been using rivers. However owing to the rise in the population and rapid industrial growth in the past 30 to 40 years, this use is being, constantly and to an alarming extent, turning to abuse.

Besides other abuses the rivers are being used for the disposal of human, agricultural and industrial waste. Through their natural flow and ecology rivers have the capacity to cleanse themselves and they can cope with surprisingly large amounts of effluent. However, any river has a limited capacity to digest sewage and absorb fertilizers washing from croplands. Whenever this capacity is exceeded, over-abundant bacteria, algae, and plant life consume all the oxygen dissolved in the water, suffocating insect and fish life, and leading to the destruction of the entire riparian ecosystem through disruption of the food chain.

EFFECTS OF RIVER POLLUTION

GENERAL

Water pollution by chemicals not normally present in the natural system can also have dire consequences, and rivers are extremely vulnerable to poisoning by toxic substances such as heavy metals (lead, zinc, cadmium), acids, solvents or chlorinated organic compounds, produced by mining, smelting, and manufacturing industries. The following are the known effects:

1. These chemicals kill during acute pollution incidents.
2. They accumulate slowly in the sediments and soils of the flood plain.
3. When the chemicals are concentrated in riparian plants growing on contaminated land, and the wildlife that feeds on those plants, mutation and infertility may lead to irreversible destruction of entire natural communities and permanent blighting of the landscape.

HUMANS :

Humans are not exempt from the dangers of pollution. Consumption of water and food from contaminated rivers and soils possess real, but largely unknown, hazards to public health. The health impact of water pollution results in:

1. Reduced life expectancies
2. Increased levels of stillbirths and congenital deformities in the worst-affected areas.
3. Doubling of cases of intestinal infections, including dysentery, typhoid, and viral hepatitis.

THE CHALLENGE :

Most rivers in the industrialized nations of the world are already polluted to a greater or lesser degree, and the challenge facing today and tomorrow’s society is not only to reduce current pollution inputs, but also to restore the natural ecology of rivers and make them safe for people to use by cleaning up toxic chemicals already residing in contaminated sediments and flood-plain soils.

The challenge in the developing world is to avoid repeating the mistakes made by the industrialized nations through preventing pollution of rivers and their ecosystems. These rivers are the last refuge of many plant and animal species and the water resources that they can supply represent the best hope for sustainable development in many nations.

The significance of the world’s rivers transcends national boundaries and local interests. Hence, river conservation and management requires a balanced approach, with developed and developing nations sharing the costs equitably in a partnership that recognizes the importance of rivers as a global natural resource.