6.5 Environmental consequences of using nitrogen fertilisers

Question 1

EXAM QUESTION

Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water. (5)

Answer 1

1. Growth of algae/surface
plants/algal bloom blocks light;
2. Reduced/no photosynthesis so
(submerged) plants die;
3. Saprobiotic
(microorganisms/bacteria);
4. Aerobically respire / use oxygen
in respiration;
5. Less oxygen for fish to respire /
aerobic organisms die;

Question 2

EXAM QUESTION

An increase in nitrate concentration in the water entering the lake could affect algae
and fish in the lake. Explain how. (5)

Answer 2

1. Algal bloom / increase in algae;
2. Algae block light / plants/algae
   die;
3. Decomposers/saprobionts/bact
   eria break down dead plant
   materials;
4. Bacteria/decomposers/saprobio
   nts use up oxygen in respiration
   / increase BOD;
5. Fish die due to lack of oxygen;

Question 3

How do nitrogen fertilisers cause reduced species diversity? (2)

Answer 3

Nitrogen-rich soil favours rapidly-growing species

Other species out-competed and die

Question 4

Define leaching 
Rain water causes? enter?
Dangers:
humans (2)
environment (1)

Answer 4

Soluble nutrients to dissolve and leach through soil out of reach of plant roots, watercourses/ bodies of water:

Humans - inefficient oxygen transport in babies, stomach cancer
Environment - eutrophication

Question 5

Define eutrophication

Process? (5)

Answer 5

The process by which nutrients build up in bodies of water.

1. Growth of algae/algal bloom
2. Algae blocks light
3. Reduced/no photosynthesis so (submerged) plants die
4. Saprobiotic microorganisms/decomposers break down dead plant materials;
5. Use oxygen in aerobic respiration
6. Less oxygen so aerobic organisms (e.g. fish) die.

Question 6

EXAM QUESTION

Suggest 2 advantages of processing waste in anaerobic digesters rather than open ponds. (2)

Answer 6

1. Gases / correct named gas not released;
2. Conditions (in digester) can be controlled;
3. Products/named product can be collected;
4. Open ponds associated with health risk/environmental
   damage/eutrophication;

Question 7

EXAM QUESTION

The over-application of fertiliser increases the rate of leaching. Explain the
consequences of leaching of fertiliser into ponds and lakes. (3)

Answer 7

1. Increase algae/algal bloom;
2. Light blocked out;
3. Plants can’t photosynthesise / plants and/or algae die;
4. Bacteria/saprobionts/EW feed off/breakdown dead
   organisms;
5. Bacteria/saprobionts/EW use up oxygen/bacteria
   respire/BOD rises;