Algal Bloom: Definition, Meaning Causes, Importance, Types

What Is an Algae Bloom?

An algal bloom is a sudden increase in the population of algae in an aquatic system, resulting in visible changes, such as water discolouration. This phenomenon can occur in both freshwater and saline environments and is influenced by physical, chemical, and biological factors. The rapid growth of algae that can alter the characteristics of the water.

Importance of Algae

Algae play a crucial role in ecosystems, and understanding algal blooms is essential for their management.

• Algal bloom research contributes significantly to our knowledge of the impact on the environment, economy, and human health.

• From an ecological perspective, algal blooms can disrupt oxygen levels in aquatic ecosystems.

• Economically, algal blooms can damage fisheries, tourism, and water treatment processes, resulting in significant financial losses.

• Moreover, certain phytoplankton blooms produce toxins that can contaminate drinking water sources, posing a threat to both human and animal health, leading to illnesses or even death.

Types of Algal Blooms

The various types of algal blooms are defined as:

Harmful Algal Blooms (HABs)

• The harmful algal blooms result from algae producing toxins poisonous to aquatic life, humans, and animals.

• Common types of harmful algae include cyanobacteria also known as blue-green algae, dinoflagellates, and diatoms.

• They result in fish kills, shellfish poisoning, and other health problems.

Non-Harmful Algal Blooms

• They do not produce toxins, but nontoxic algal blooms still have major ecological implications.

• For example, they can produce hypoxia, which creates dead zones where no aquatic life can live.

• It can block sunlight from going down to underwater plants and throw off the aquatic food chain.

Cause of Algal Bloom

Algal blooms are caused by these reasons:

Nutrient Pollution (Nitrogen And Phosphorus)

The excess nutrients, mostly nitrogen and phosphorus, are key reasons behind algal blooms. These nutrients enter into the water from agricultural runoff, discharging of wastewater, or other industrial processes. High nutrient levels increase the growth rate of algae, promoting blooms.

Light Availability

Light is another essential element required in algal blooms. It is linked to photosynthesis and high light availability in clear shallow waters favours high populations of algae.

Water Temperature

Most blooms occur in summer. Climate change is, therefore, raising the water temperature, likely to lead to significantly more frequent and serious algal blooms.

Water Movement and Stability

Stable water conditions of stagnant or slow-flowing waters tend to favour algal blooms. On the contrary, the turbulent nature of waters can disperse algae and limit bloom formation. Human activities, in particular on rivers by way of damming and flow alteration, create the perfect conditions for blooms.

Algal Bloom NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Types of algal bloom

• Causes of algal bloom

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 Algal Bloom

• Types of Pollution

• Solid Waste Management

Recommended Video for Algal Bloom