Too much fertiliser

The idea

Excess nitrates from overused fertilisers reach rivers and lakes and cause algal blooms that deplete oxygen and kill fish; this process is eutrophication.

A green pond

After heavy use of fertiliser in the fields, a nearby pond turns thick green.

What do you think happens to the fish?

• They may die for lack of oxygen
• They grow faster
• Nothing happens to them

From field to pond

Press Next step.

Eutrophication

Fertiliser feeds the algae, the algae use up the oxygen, and the fish cannot breathe. This process has a name, eutrophication. It threatens water bodies and coastal fisheries.

Excess nitrates from overused fertilisers reach rivers and lakes and cause algal blooms that deplete oxygen and kill fish. This process is eutrophication.

Notes

Excess nitrates from overused fertilisers cause algal blooms that deplete oxygen and kill fish: eutrophication.

Check yourself

What adds excess nitrogen as nitrates to rivers and lakes?

What do the excess nitrates cause in rivers and lakes?

What happens to the oxygen in the water and to the fish?

What is the process of nitrates causing algal blooms, oxygen loss and fish deaths called?

• Lightning in the clouds. Lightning fixes nitrogen as nitrogen oxides in the air. The excess nitrates in the water come from overused fertilisers.
• Planting trees. The chapter names overuse of fertilisers as the source of the excess nitrates.
• Overuse of fertilisers in agriculture — correct. Yes!
• Widespread growth of algae, called algal blooms — correct. Yes!
• Clear water. The nitrates cause widespread growth of algae, called algal blooms.
• More oxygen in the water. The algal blooms deplete the oxygen in the water.
• Oxygen increases and fish multiply. Algal blooms deplete oxygen and kill fish.
• Oxygen is depleted and fish die — correct. Yes!
• Oxygen stays the same and fish are not affected. The algal blooms deplete the oxygen, which kills fish.
• Denitrification. Denitrification converts some nitrates back into nitrogen gas.
• Nitrification. Nitrification converts ammonia into nitrite and then nitrate.
• Eutrophication — correct. Yes!