Learning outcomesStudents should understand the followingThe environmental issues arising from the

use of fertilisers. Leaching and eutrophication.

Candidates should be able to analyse, interpret and evaluate data relating to eutrophication.

FertilisersFertilisers are very effective but also have

undesirable effects on the environment:

• Reduced species diversity – nitrogen rich soils favour fast growing species (e.g. grasses and nettles)

•Since nitrate and ammonium ions are very soluble, they do not remain in the soil for long and are quickly leached out, ending up in local rivers and lakes and causing eutrophication.

LeachingRain will dissolve soluble

nutrients removing them from the reach of plant roots and eventually releasing them into watercourses.

Very high levels of nitrates in drinking water can prevent efficient oxygen transport in babies and may be linked to stomach cancer.

Leaching of nitrates can also harm the environment, leading to eutrophication.

Eutrophication Oligotrophic - a lake that has a low level of

nutrients.It has clear water and can support a small

population of organisms.

Eutrophic – a lake enriched with nutrients.The water is cloudy because of the presence

of large numbers of algae and cyanobacteria.

Eutrophication is a natural process that takes place over a long period of time.

Eutrophication In the context of pollution "eutrophication" has

come to mean a sudden and dramatic increase in nutrients due to human activity, which disturbs and eventually destroys the food chain.

The main causes are fertilisers leaching off farm fields into the surrounding water course, and sewage (liquid waste from houses and factories).

These both contain dissolved minerals, such as nitrates and phosphates, which enrich the water.

Eutrophication

Th

e p

rocess o

fEu

trop

hic

ati

on

Limiting factor - minerals

Limiting factor - light

The process of Eutrophication cont.

Limiting factor - oxygen

Biochemical oxygen demand (BOD)This measures the rate of oxygen consumption

by a sample of water, and therefore gives a good indication of eutrophication.

A high BOD means lots of organic material and aerobic microbes, i.e. eutrophication.

Aquatic ecosystems can slowly recover from a high BOD as oxygen dissolves from the air, but long-term solutions depend on reducing the amount of minerals leaching into the water.

Reducing leaching can be achieved by applying inorganic fertilisers more carefully, by using organic fertilisers, by using low-phosphate detergents, and by removing soluble minerals by precipitation in modern sewage plants.

As a last resort eutrophic lakes can be dredged to remove mineral-rich sediment, but this is expensive and it takes a long time for the ecosystem to recover. This has been done in the Norfolk Broads.

(a) Why do plants need ions which contain nitrogen?(1)

(b) (i)Explain why it is necessary for farmers to apply

fertilisers to land that is used annually to grow a cereal crop.(2)

(ii) Explain what is meant by the law of diminishing returns

with respect to the application of artificial fertilisers.(2)

(a) (i) protein / amino acid production 1 (b) (i) increased yields;

replace ions taken in by crop; 2 (ii) increased application of fertiliser does not increase yields;

therefore uneconomic 2

Exam question

(c)The graph shows the relationship between nitrate application to farmland and the concentration of nitrate in a nearby reservoir.

(i) Explain why there was an overall increase in the concentration of nitrate of nitrate in the reservoir between 1960 and 1990. (1)

(ii)Suggest one explanation for the large fall in nitrate concentration in the reservoir between 1982 and 1984. (2)

(d) Explain why there is concern at the amount of nitrates being leached into rivers, lakes and reservoirs. (4)

(Total 12 marks)

2 5

2 0

1 5

1 0

5

0

1 2 5

1 0 0

7 5

5 0

2 5

0

N itra teap p lic a tion tofa rm lan d/k g p er h ec ta rep er y ear

N itra teco n c en tra tio nin re serv o ir/m g p er litre

1 9 6 0 1 9 6 5 1 9 70 19 7 5 1 9 8 0 1 9 8 5 19 9 0Year N itra te ap p lic a tio n

to fa rm la n dN itra te co n ce n tra tio nin re serv o ir

(c)(i) increased leaching as result of increased application1

(ii) Eitherincreased rainfall (leading to increased volume of water flowinginto reservoirs);increased volume leads to increased dilution of nitrateOrless rain;therefore more uptake by crop / less leaching 2

(d) increased growth of plants / algae;

(leading to) eutrophication;increase in microorganisms feeding on dead plants / algae;leading to deoxygenation;increased nitrate in drinking water;causing human illness 4

[12] 

Task Read the application – Troubled waters- on

p101 and answer the questions 1-4

Learning outcomesStudents should understand the followingThe environmental issues arising from the

use of fertilisers. Leaching and eutrophication.

Candidates should be able to analyse, interpret and evaluate data relating to eutrophication.