Causes, Effects and Solutions to Eutrophication

What is Eutrophication?

Eutrophication presents as one of the most serious ecological problems of open water sources such as lakes, oceans and reservoirs. It is characterized by dense algal and plant growth owing to the enrichment by phosphorus and nitrogen nutrients needed for photosynthesis. As a result, it often contributes to the formation of extensive mats of floating plants. Examples of the plants include algal blooms, Nile cabbage and water hyacinths.

The nutrients come from animal wastes, fertilizers and sewage which are washed by rain or irrigation into the water bodies through surface runoff. Eutrophication can also take place naturally over thousands of years as the lakes grow old and get filled with sediments. Human activities top the list that speeds up the degree and rate of eutrophication through both point-source and non-point source discharges of the chemical nutrients (phosphates and nitrates) into water systems.


Below are few of the causes, effects and solutions to Eutrophication.

Causes of Eutrophication

  1. Fertilizers (nitrates and phosphates)

Eutrophication is predominantly caused by human action due to the dependence on using nitrate and phosphate fertilizers. Agricultural practices and the use of fertilizers on lawns, golf courses and other fields contribute to phosphate and nitrate nutrient accumulation.

When these nutrients are washed by surface runoff into lakes, rivers, oceans and other surface waters when it rains; the hungry plankton, algae and other aquatic plant life are well fed and their photosynthesis activity is increased. This causes dense growth of algal blooms and plant life such as the water hyacinths in the aquatic environments.

  1. Concentrated animal feeding operations

Concentrated animal feeding operations (CAFOs) are as well a main contributor of phosphorus and nitrogen nutrients responsible for eutrophication. The concentrated animal feeding operations normally discharge high scores of the nutrients that find way into rivers, streams, lakes and oceans where they accumulate in high concentrations thereby plaguing the water bodies by recurring cyanobacterial and algal blooms.

  1. Direct sewage discharge and industrial waste into water bodies

In some parts of the world, especially the developing nations, sewage water is directly discharged into water bodies such as rivers, lakes and oceans. As a result, it introduces high amounts of chemical nutrients thereby stimulating the dense growth of algal blooms and other aquatic plants which threatens survival of aquatic life in many ways.

Some countries may also treat the sewage water, but still discharge it into water bodies after treatment. As much as the water is treated, it can still cause the accumulation of excess nutrients, ultimately bringing about eutrophication. The direct discharge of industrial waste water into water bodies presents similar outcomes.

  1. Aquiculture

Aquiculture is a technique of growing shellfish, fish and even aquatic plants (without soil) in water containing dissolved nutrients. As a highly embraced practice in the recent times, it also qualifies a top ranking contributor to eutrophication.

If aquiculture is not properly managed, the unconsumed food particles together with the fish excretion can significantly increase the levels of nitrogen and phosphorous in the water thereby resulting in dense growth of microscopic floating plants.

  1. Natural events

Natural events such as floods and the natural flow of rivers and streams can also wash excess nutrients off the land into the water systems thus causing excessive growth of algal blooms. Also, as lakes grow old, they naturally accumulate sediments as well as phosphorus and nitrogen nutrients which contribute to the explosive growth of phytoplankton and cyanobacterial blooms.

Effects of Eutrophication

  1. Threatens the survival of fish and other aquatic life forms

When aquatic ecosystems experience increased nutrients, the phytoplankton and other photosynthetic plants grow explosively, commonly known as algal blooms. As an outcome, the algal blooms limit the amount of dissolved oxygen required for respiration by other animal and plant species in the water. Oxygen depletion happens when the algae/plant life die and decompose.

When the dissolve oxygen reaches hypoxic levels, the animal and plant species under the water such as shrimp, fish and other aquatic biota suffocate to death. In extreme cases, the anaerobic conditions encourage the growth of bacteria that produces toxins which are deadly to the marine mammals and birds. The growth of phytoplankton also causes reduced light penetration into the lower depths of the water. This can bring about aquatic dead zones, loss of aquatic life and it also lessens biodiversity.

  1. Deterioration of water quality and limits access to safe drinking water

Algal blooms are highly toxic and once the water reaches the anaerobic conditions, the growth of more toxic bacterial is promoted. The consequence is extensive deterioration of water quality and decline in the availability of clean drinking water. The dense growth of algal blooms and photosynthetic bacteria in surface waters can also block water systems hence limiting the availability of piped water.

On this regard, toxic algal blooms have shut down numerous water supply systems across the globe. In 2007, for instance, more than 2 million residents of Wuxi, China could not access piped drinking water for more than a week due to severe attack by algal blooms on Lake Taihu.

  1. Poisoning and impact on human health

The cyanobacteria, also referred to as dinoflagelates which generates red tide, release very powerful toxins with high poison levels in the water even at very low concentrations. The anaerobic conditions created by explosive plant growth in the water also results in the doubling of the toxic compounds.

It can also cause death in humans and animals even at the least concentration when ingested in drinking water. Besides, freshwater algal blooms can threaten livestock health. The toxic compounds can also make their way up the food chain, contributing to various negative health impacts such as cancers. Biotoxins are linked to increased incidence of neurotoxic, paralytic and diarrhoetic shelfish poisoning in humans, which can lead to death.

The shellfish accumulate the poison in their mussles and then poisions humans upon consumption. High nitrogen concentraion in drinking water is associated with the ability of inhibiting blood circulation in infants, a condition known as blue baby syndrome.

  1. Endangers fishing

One of the main characteristic of eutrophication is the increased growth of minute floating plants such as algae and photosynthetic bacteria and the development of extensive and dense mats of floating plants such as Nile cabbage and water hyacinths. Whenever this happens on a water body, fishing is endangered. It simply becomes difficult to set the fishing nets in water and the plants floating on water limits the mobility of boats and other fishing vessels.

  1. Degradation of recreational opportunities

The main problem of eutrophication is the algal blooms and other aquatic plants that float on an extensive area of the water surface. It reduces the transparency and navigation in the water which lessens the recreational values and opportunities of the lakes, especially for boating and swimming. Nile cabbage, algal blooms, and water hyacinth can spread over an extensive area along the shores and can sometimes float over the entire surface into the land area.


Solutions to Eutrophication

  1. Composting

Eutrophication mainly arises from the use of nitrate and phosphate fertilizers. In a bid to address the phenomenon, composting can be used as a solution. Composting is the practice of converting organic matter such as food residues and decaying vegetation into compost manure.

The nutrients present in the compost manure are deficient of the high concentration of nitrates and phosphates that feed the algae and other microbes in water bodies. In compost fertilizer, all the essential elements are broken down and synthesized by the plants thereby not creating the cycle of eutrophication. This method of controlling eutrophication is termed as nutrient limitation.

  1. Reducing pollution

Just like composting, limiting pollution is an easy and effective method of cutting back on the amount of nitrogen and phosphates discharged into water systems. Big manufacturing companies and municipalities ought to reduce pollution and desist from discharging waste into water systems so as to reduce the amount of toxins and nutrients ending up in the waters that feed the algae and other microscopic organisms.

If industries and municipalities can cap their waste discharge and pollution to a lower level, then nutrient content is reduced in the water systems which can subsequently control eutrophication.

  1. Strengthening laws and regulations against non-point pollution

Strengthening laws and regulations against non-point water source pollution can substantially control eutrophication. According to EPA, non-point pollution presents the most serious challenge in the management of nutrient entry into water systems. Controlling nutrient sources therefore results in decreased eutrophication.

By minimizing non-point pollution, we are essentially lessening the amount of nutrients entering the aquatic ecosystems. The laws should aim at enhancing high water quality standards and zero-tolerance to non-point solution. With the support of policymakers, citizens, pollution regulatory authorities and the government, it is easy to control eutrophication.

  1. Ultrasonic Irradiation

The world is constantly seeking advanced methods for resolving some of the environmental problems. When it comes to eutrophication, the use of ultrasonic irradiation is one such mechanism which has been exploited as an alternative solution to control and manage algal blooming. The process works by causing cavitations which produces free radicals that destroy algae cells. Still, research is still underway to determine the uniqueness of its use in controlling the eutrophication problem.

Reference: NOAA , Nature
Image credit: flickr , flickr


Rinkesh is passionate about clean and green energy. He is running this site since 2009 and writes on various environmental and renewable energy related topics. He lives a green lifestyle and is often looking for ways to improve the environment around him.