Question

What is the condition of the river today? What impacts are affecting the river and how has it changed?

Answer 1

ANS)

Today rivers are suffering from water pollution. Water pollution is a major environmental issue nowadays. The largest source of water pollution is untreated sewage.Other sources of pollution include agricultural runoff and unregulated small scale industry. Most rivers, lakes and surface water are polluted due to industries, untreated sewage and solid wastes.

Discharge of untreated sewage is the single most important source of pollution. Organic and bacterial contamination is severe in water bodies nowadays.

Several key areas of human impact on river ecosystems are:

• pollution
• flow modifications
• exotic species
• harvesting.

Pollution

Pollution is difficult to control because it is often the result of human infrastructure around a river. Pollution enters the river, sometimes in small amounts, at many different locations along the length of the river. Common sources of pollution come from rural and urban areas.

The clearing of forests to produce farmland has led to on-going erosion, with large quantities of sediment deposited into rivers. Agricultural intensification (substantial increases in fertiliser application and increased stock numbers) has resulted in nutrient and chemical loss to nearby streams and rivers. Elevated nutrient concentrations (especially nitrogen and phosphorus – key components of fertilisers) can result in the eutrophication of slow-moving waterways.

Urban areas add to this pollution when contaminants (PAHs and heavy metals) are washed off hard surfaces such as roads and drain into water systems. Sulfur dioxide and nitrous oxide emitted from factories and power stations enter river systems through acid rain. Sewage and effluent are discharged into rivers in some areas.

Pollution can lower the pH of the water, affecting all organisms from algae to vertebrates. Biodiversity decreases with decreasing pH.

Flow modifications

Dams alter the flow, temperature and sediment in river systems. Reduced flow alters aquatic habitats – reducing or removing populations of fish, invertebrates and plants that depend on the flow to bring food. Reduced flow also decreases tributary stream flow, changing habitats and altering the water table in the stream aquifer. Consequently, riverside vegetation may be affected and decline in numbers. This may affect animal biodiversity, for example, bird species may leave the area if their habitat is lost or altered.

Changes in water temperature due to flow modification can affect insect development by not allowing them to complete their life cycle.

Rivers are connected systems, and barriers such as dams, culverts and floodgates disconnect one area from another. They prevent species such as eels from migrating, isolating previously connected populations.

Water taken from rivers for irrigation can lower river flows.

Exotic species

Exotic species have been introduced to river systems sometimes intentionally (for example, for fishing purposes or as food for other species) and sometimes unintentionally (for example, species come in on the bottom of boats or on fishing gear or they escape from pond areas during flooding, such as koi carp).

These organisms can affect native species. They may compete with them for prey and habitat. They may prey on native species, alter habitats, breed with native species to produce another species or they may introduce harmful diseases and parasites. Once established, these species can be difficult to control or eradicate, particularly because of the connectivity of the flowing river. They can easily migrate to many areas affecting native species.

Harvesting

Excessive fishing in river ecosystems can drastically reduce numbers of species. For example, numbers of eels and whitebait in the Waikato River have reduced since the 1970s. Commercial eeling began in the 1960s and peaked in the 1970s with an annual average catch of 2000 tonnes. In the early 1980s, 400–450 tonnes per annum were harvested, with less than 200 tonnes per annum harvested since 2000.

Whitebait tonnage has also drastically reduced from an average of 46 tonnes per annum in the 1950s to 3 tonnes in 2000. Reducing stocks of a particular species can have an effect on other species such as birds that feed off river fish. The birds leave the area when river fish decline.

Eliminating agricultural pollution

Pollution in rivers is either “point source” such as industrial sewage, which enters the river in high volumes from a few locations or “non-point source”, such as agricultural runoff, which can enter the river from thousands of locations along its course. Agricultural runoff is harmful to rivers because of the use of chemicals for cultivation, which has become the norm today. This can be rectified if farmers are supported to move to organic cultivation. This is not only good for the river, it is also good for the soil, the farmer’s income and public health.

Farmers are coming to their senses and hence shifting to organic cultivation rather than use of chemicals. It is also essential to ensure the food security of the nation and the well-being of hundreds of millions of farmers.

Treating industrial and chemical waste

Point source pollution is generally chemical and industrial waste from industries or domestic sewage from towns and cities. One important aspect in towns and cities is that just as electricity, water and gas are metered, sewage should be too, with households and industries paying according to the meter.

Right now the way chemical and industrial waste is handled is that the polluting industry itself is expected to clean its effluent before letting it out into the river. In effect, this just leads to many industries treating their effluent wastes using sophisticated technologies before letting them out into rivers.

Hence we can see changes or improvements in the way river water was treated earlier.

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