Eutrophication + Pollution of Water

Question 1

why do farmers use fertilisers?

Answer 1

to increase the yield of their crops

Question 2

what do fertilisers usually contain?

Answer 2

nitrates and phosphates - these are very soluble in water

Question 3

what is leaching?

Answer 3

when a lot of fertiliser is present on farmland surrounding a river it is washed out of the soil when it rains into the river

Question 4

what are the effects of leached nitrates?

Answer 4

• the nitrates are absorbed by the green algae in the water
• these multiply rapidly and may completely cover the water - the great growth of algae is called algal bloom
• this blocks out the sunlight for other plants in the river or lake
• this mean that they are unable to synthesise and die
• even the algae on the top eventually die
• the dead remains provide good source of food for bacteria
• the bacteria multiply rapidly
• the large population of bacteria respire, increasing the biological oxygen demand - using up oxygen in the water
• this decreases the level of oxygen and results in the death of other organisms in the water, as they cannot respire aerobically
• this whole process is called eutrophication

Question 5

how does sewage enter water supplies?

Answer 5

due to leaking pipes, or run off from farm land

Question 6

what is sewage?

Answer 6

undigested food material - it contains lots of biological molecules, including carbohydrates, proteins, nucleic acids and fats

Question 7

how does sewage pollute water?

Answer 7

• the sewage provide a good source of food for bacteria
• the bacteria therefore multiply rapidly
• the large population of bacteria respire, increasing the biological oxygen demand, using up oxygen in the water
• this decreases the level of oxygen and results in the death of other organisms in the water, as they cannot respire aerobically
• this is different from eutrophication as it does not involve an algal bloom