Eutrophication: Definition, Causes, Classification, Types, Effects, Topics

What Is Eutrophication?

Eutrophication is an anthropogenic process in which water bodies such as lakes, rivers, and coastal areas are overly enriched with excessive nutrient loading, chiefly nitrogen and phosphorus. Sources include agriculture, urban runoff, and industrial discharges of nutrients into aquatic systems. Consequently, this leads to the explosive growth of algae and other water plants, which may turn out ecologically to be unbalanced.

Causes Of Eutrophication

This primarily leads to eutrophication in water bodies, where there are abundant nutrients, especially nitrogen and phosphorus, caused by the excessive input.

Agricultural Runoff

• Fertilisers rich in nitrates and phosphates

• Pesticides washed into rivers and lakes

Atmospheric Deposition

• Further accelerated by atmospheric deposition of nitrogen compounds caused by the burning of fossil fuels.

Industrial Discharges

• Effluents containing nutrients and chemicals

Urban Runoff and Sewage

• Another pathway is urban runoff, which is composed of sewage effluents and detergents.

• Detergents containing phosphates promote excessive growth of algae.

Process Of Eutrophication

Eutrophication is a process that begins with nutrient enrichment, which is the excessive supply of nitrogen and phosphorus to the water body. This causes algal blooms to form, which is an event of rapid growth in algae and other phytoplanktons. This oxygen reduction may promote death in aquatic animals, causing an imbalance in the ecosystem.

• Nutrient enrichment of water body

• Rapid algal bloom formation

• Blocking of sunlight to submerged plants

• Death and decomposition of algae

• Oxygen depletion (hypoxia/anoxia)

• Death of fish and aquatic organisms

• Formation of dead zones

Classification Of Eutrophication

Eutrophication is of two forms: natural and cultural.

Natural eutrophication

• It is the slow process over centuries as water bodies age and accumulate natural nutrients and sediments.

Cultural eutrophication

• It is a result of the speeding up of these natural processes caused by human activities that have led to fast nutrient enrichment and changed ecology.

Based on Nutrient Source

Eutrophication can also be categorised based on the source of nutrition.

• Point source eutrophication pertains to nutrient fertilisation by discernible sources, usually discharged from wastewater pipes.

• Non-point source eutrophication, meanwhile, results from markedly dispersed and distant sources, such as agricultural runoff and atmospheric deposition, and therefore becomes less readily controllable.

Fate of Algal Biomass In Eutrophic Water

Massive algal blooms in eutrophic waters finally decay and die. Decomposition absorbs considerable amounts of oxygen and causes the water to turn into a hypoxic if not anoxic, condition. That is, the oxygen concentration in the water reduces considerably, reaching a level at which most fishes and other aquatic organisms cannot live beyond a survival threshold. This is what might lead to dead zones with minimal aquatic life.

Effects Of Eutrophication

The effects of Eutrophication are:

Environmental Impact

• Eutrophication results in the loss of biodiversity because oxygen-depleted waters do not support a large variety of aquatic life.

• Water quality change does not just affect the aquatic ecosystem alone.

• It also means the organisms that depend on this aquatic ecosystem are also affected.

• Hypoxia and anoxia create dead zones that most aquatic life cannot survive in.

Economic Impact

• Eutrophication reduces the population of fish as a result of decreasing levels of oxygen.

• It also reduces the fishing industry, which brings losses to the economy within the community.

• In addition, the price of water treatment increases because the eutrophic waters need intensive purification to make them drinkable.

Social Effect

• Eutrophication deteriorates recreational activities like swimming, boating, and fishing, causing a change in tourism.

• Public health impacts result from harmful algal blooms that grow in eutrophic waters, releasing toxins into bodies of water used for drinking supplies and hence causing a problem for human health.

Mitigation And Control Measures

Following are the control measures for Eutrophication

Prevention Strategies

Prevention strategies includes, for example, buffer strips and the correct use of fertilizers to reduce nutrient runoff from agriculture. Urban planning is necessary concerning effective wastewater treatment and developing green infrastructure for good stormwater management.

Restoration Techniques

Aeration along with enhanced oxygen levels and biomanipulation, changing the food to lower the algal blooms, are two ways toward restoring eutrophic water bodies.

Policy and Legislation

Effective policies and laws are essential in eutrophication management. Water quality standards shall be defined and maintained through the limitation of nutrient discharge. Promotion of good practices can be done through international agreements and collaboration between states.

Eutrophication NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Causes of eutrophication

• Effects of eutrophication

Practice Questions for NEET

Q1. A higher biochemical oxygen demand in a particular segment of a river indicates that

1. the segment is free from pollution

2. the segment is highly polluted

3. aquatic life has started flourishing

4. the river has high number of aquatic animals

Correct answer: 2) the segment is highly polluted

Explanation:

A higher BOD in a river segment signifies organic pollution. BOD quantifies oxygen utilised by microbes to decompose organic substances like sewage and decaying plants. An elevated BOD implies increased organic content, necessitating more oxygen. This excessive demand can deplete water oxygen, adversely impacting aquatic life by decreasing available oxygen for fish and similar organisms.

Hence, the correct answer is option 2). The segment is highly polluted.

Q2. A lake which is rich in organic waste may result in

1. increased population of aquatic organisms due to minerals

2. drying of the lake due to algal bloom

3. increased population of fish due to lots of nutrients

4. mortality of fish due to lack of oxygen

Correct answer: 4) mortality of fish due to lack of oxygen

Explanation:

Eutrophication: The rich growth of micro-organisms consumes most of the dissolved oxygen, to deprive other organisms. It generally occurs at the bottom layers of deep lakes. The addition of excessive plant nutrients intensifies eutrophication. It is harmful to fish and other aquatic life.

A lake rich in organic waste will reduce the dissolved oxygen. The organic waste will increase the biological oxygen demand of the lake thus depleting the O2 content and may result in the death of fish.

Hence, the correct option is 4) mortality of fish due to lack of oxygen.

Q3. The amount of biodegradable organic matter in sewage water can be estimated by measuring.

1. Biochemical oxygen demand

2. The growth of anaerobic bacteria in water

3. Biogeological oxygen demand

4. The growth of aerobic bacteria in water.

Correct answer: 1) Biochemical oxygen demand

Explanation:

BOD is the quantity of oxygen needed by microbes to decompose the organic matter in water during a predetermined time frame, often five days at 20°C. Because microorganisms need more oxygen to break down organic material, a greater BOD denotes a larger degree of organic pollution. This measurement is crucial for evaluating the quality of water and figuring out how polluted sewage or wastewater is.

Hence, the correct answer is option 1)Biochemical oxygen demand.

Also Read:

• MCQs on Eutrophication and Thermal Waste

• Types of Pollution

• Solid Waste Management

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