Eutrophication

Which of the following is NOT a source of nitrates and phosphates into a river?

• Fertilizers

• Animal waste

• Wastewater

• Burning fossil fuels

What is the very next thing that happens after fertilisers enter a river in eutrophication?

• Fish die due to a lack of oxygen

• Plants below the surface die due to a lack of sunlight

• The number of aerobic bacteria increases

• Fast growth of plants

In eutrophication, what directly causes the death of fish?

• The plants use up oxygen in respiration

• The fish are poisoned by high CO₂ levels

• Bacteria use up oxygen in respiration

• The fish use up oxygen in respiration

In eutrophication, what does 'algal bloom' refer to?

• The rapid increase in the number of bacteria

• The rapid increase in the number of plants

• The rapid decrease in the number of fish

• The rapid increase in the amount of nitrates in the river

Eutrophication is defined as a change that occurs to an aquatic ecosystem. This change is mainly due to what?

• Newly introduced fish

• Depletion of the ozone layer

• Increased nutrient concentration

• Increase in atmospheric carbon dioxide.

Which is the correct order of changes that occur during eutrophication?

• Aquatic plants cannot photosynthesize and die. Algal blooms blocks light from entering lower levels of a pond or lake. The fish and other aquatic organisms die. The bacteria decompose the algae, and they use up a lot of oxygen during this process. The algae die.

• Algal blooms blocks light from entering lower levels of a pond or lake. Aquatic plants cannot photosynthesize and die. The algae die. The fish and other aquatic organisms die. The bacteria decompose the algae, and they use up a lot of oxygen during this process.

• Algal blooms blocks light from entering lower levels of a pond or lake. Aquatic plants cannot photosynthesize and die. The algae die. The bacteria decompose the algae, and they use up a lot of oxygen during this process. The fish and other aquatic organisms die.

• Aquatic plants cannot photosynthesize and die. Algal blooms blocks light from entering lower levels of a pond or lake. The bacteria decompose the algae, and they use up a lot of oxygen during this process. The algae die. The fish and other aquatic organisms die.

The green plants on the surface of the lake turned out the be algae! There is a sudden increase in the rate of growth of the algae. What would happen next?

• The algae continue to grow due to excess nutrients, and some of the algae die

• The algae would stop growing

• The algae are not affected by the fertilisers

Why do nitrates and phosphates cause algal blooms?

• They are critical plant nutrients.

• They kill off competition.

• Because algae grow faster than decomposers.

• Nitrates and phosphates are density independent limiting factors.

In eutrophication, dissolved oxygen levels decrease because

• decomposers use it in cellular respiration

• algae bloom and use it up

• plant nutrients react with the dissolved oxygen

• fish use it up