River Pollution: Understanding The Contamination Of Waterways

Water pollution is a pressing issue that affects the lives of one in three people worldwide, according to the United Nations. Unsafe water kills more people each year than war and all other forms of violence combined. Rivers are particularly vulnerable to pollution, as contaminants from a range of human activities can easily enter their waters. From chemical dumping to plastic waste, rivers are facing a constant onslaught of pollutants that degrade water quality and endanger both human and environmental health.

Human activity

Water pollution also occurs when harmful substances, often chemicals or microorganisms, contaminate a river, degrading water quality and rendering it toxic to humans or the environment. This widespread problem jeopardizes our health, with unsafe water killing more people each year than war and all other forms of violence combined. Water pollution is caused by contaminants such as chemicals, nutrients, and heavy metals, which are carried from farms, factories, and cities by streams and rivers into bays and estuaries. Marine debris, particularly plastic, is blown in by the wind or washed in via storm drains and sewers.

Oil spills and leaks, big and small, spoil the ocean and rivers, and the transportation and storage of oil and its derivatives are subject to leakage that pollutes water resources. The UN states that more than 80% of the world's sewage finds its way into seas and rivers untreated. Much of the plastic pollution in the ocean comes from fishing boats, tankers, and cargo shipping.

Human sewage and effluent are discharged into rivers in some areas. This can lower the pH of the water, affecting all organisms from algae to vertebrates. Biodiversity decreases with decreasing pH. Dams also alter the flow, temperature, and sediment in river systems. Reduced flow can alter aquatic habitats, reducing or removing populations of fish, invertebrates, and plants that depend on the flow to bring food.

River water pollution is a growing environmental concern, affecting ecosystems and human health. Lack of awareness and education is a critical factor that hinders effective action against river pollution. Without this awareness, there might be a lack of motivation to take concrete steps to protect rivers and prevent pollution.

Chemical waste

Industrial processes often generate large quantities of chemical waste, which can be accidentally discharged into rivers. For example, chemicals such as cyanide, zinc, lead, copper, cadmium, and mercury may be released into the water in high concentrations, immediately killing fish and other aquatic organisms. These chemicals can also accumulate in the food chain, eventually reaching toxic levels and causing the death of birds, fish, and mammals.

Agricultural activities, such as the use of fertilizers and pesticides, also contribute to chemical waste in rivers. When it rains, these chemicals, along with animal waste from farms and livestock operations, are washed into nearby waterways. Nutrient pollution, caused by excess nitrogen and phosphorus, is a particular concern. It can lead to the growth of toxic blue-green algae, known as eutrophication, which harms both people and wildlife.

Improper waste disposal is another significant source of chemical waste in rivers. This includes municipal and industrial waste discharges, as well as random junk dumped directly into waterways. Contaminants such as chemicals, nutrients, and heavy metals can be carried from farms, factories, and cities into rivers and estuaries, eventually making their way out to sea.

The release of heat energy into rivers, often from power plants or industrial cooling processes, is also considered a form of chemical pollution. The increased water temperature lowers the level of dissolved oxygen, disrupting the balance of life in the water and endangering species such as trout that require well-oxygenated environments.

While there are chemical treatments available for remediating polluted river water, they are often temporary and may produce secondary wastes. Therefore, it is crucial to focus on sustainable strategies and strict policy controls to prevent and manage chemical waste pollution in rivers.

Plastic pollution

A recent study by The Ocean Cleanup revealed that over 1,000 rivers contribute to nearly 80% of global annual riverine plastic emissions, which range from 0.8 to 2.7 million metric tons per year. This finding highlights the extent of the problem, as previously, only a handful of large rivers were believed to be the main sources of plastic pollution in oceans. The remaining 20% of plastic emissions are distributed across 30,000 other rivers worldwide.

Several factors contribute to plastic pollution in rivers. One significant factor is improper waste disposal. When plastic waste is not properly managed, it can easily find its way into waterways, particularly rivers. These include large rivers like the Nile, Amazon, and Yangtze, which are among the top contributors to ocean plastic pollution. However, it is now understood that smaller rivers in densely populated urban areas, such as the Pasig River in the Philippines, can also be significant sources of plastic pollution. This shift in understanding underscores the need for more complex and costly solutions to address the pervasive spread of plastic waste.

The impact of plastic pollution in rivers extends beyond the rivers themselves. As plastic waste accumulates in rivers, aquatic species, such as insects and snails, are increasingly choosing to settle on plastic surfaces rather than natural habitats like rocks or branches. This alteration in behavior further exacerbates the ecological disruption caused by plastic pollution.

To address the issue of plastic pollution in rivers, a multi-faceted approach is necessary. This includes improving waste management practices, raising public awareness, implementing mitigation measures, and supporting organizations like The Ocean Cleanup, which develops technologies to intercept and remove plastic waste from rivers before it reaches the oceans.

Eutrophication

Cultural eutrophication is a significant issue in rivers, where nutrient pollution causes algal blooms and dense growths of aquatic vegetation and phytoplankton. These blooms and vegetation can shade the deeper waters, reducing the viability of benthic plants that provide shelter for fish and other organisms. The excessive growth of algae and bacteria further depletes the oxygen in the water, creating anoxic conditions that are harmful to aquatic life, including fish and shellfish.

Fertilizer runoff from farms is a common cause of eutrophication in rivers. When large amounts of fertilizer drain into a river, the concentration of nitrates and phosphates increases significantly. Algae use these nutrients to grow and multiply rapidly, leading to a dense algal bloom that turns the water green. This process, known as eutrophication, can result in the depletion of oxygen in the water, causing the death of many aquatic organisms.

The retention time of water in rivers also plays a crucial role in eutrophication. Long retention-time rivers, where water remains in the system for extended periods, are more likely to transition from being dominated by macrophytes (submerged aquatic plants) to being dominated by phytoplankton. In contrast, short retention-time rivers, with faster-flowing water, tend to exhibit benthic and filamentous algal domination.

Mercury and other heavy metals

Human activities that contribute to mercury and other heavy metal pollution in rivers include industrial, agricultural, and domestic sources. Industries such as coal washery, steel, food processing, plastic processing, metallic work, and leather tanning release large amounts of wastewater containing these metals. This wastewater is then discharged into rivers, either directly or indirectly through sewage systems. In the case of the Ganga River in India, a daily industrial wastewater equivalent of 260 million liters is released into the river, according to a report by the Central Pollution Control Board (CPCB).

Agricultural activities also play a significant role in heavy metal contamination. The use of fertilizers, pesticides, and manure can introduce heavy metals into the water through runoff or drainage. Additionally, the proliferation of urban landscapes and the use of chemical fertilizers in agriculture have further increased the levels of toxic metal contaminants in rivers via urban drainage networks and stormwater runoff management systems.

Natural processes also contribute to the presence of heavy metals in rivers. For example, mercury can be released from natural sources such as volcanic eruptions or forest fires. However, human activities have significantly increased the levels of mercury and other heavy metals in rivers beyond what would occur naturally.

The impact of mercury and other heavy metal pollution in rivers is far-reaching. These metals tend to accumulate in sediments and are then taken up by aquatic organisms, leading to bioaccumulation in the food chain. This can result in various health issues for humans who consume contaminated fish or other aquatic organisms, including liver damage, kidney damage, cancer, mental disorders, and reproductive problems. Therefore, it is crucial to continuously monitor and manage heavy metal pollution in rivers to protect both aquatic ecosystems and human health.

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