Environmental issues concerning use of nitrogen-containing fertilisers

Question 1

what are the 2 main detrimental impacts of nitrogen-containing fertilisers?

Answer 1

1- leaching which may lead to pollution of watercourses

2- eutrophication caused by leaching of fertilisers into watercourses

Question 2

explain what leaching is and its impacts

Answer 2

• leaching is the process by which nutrients are removed by the soils
• rainwater will dissolve any soluble nutrients such as nitrate ions and carry them deep into the soil eventually beyond the reach of plant roots
• the leached nitrate ions find their way into watercourses such as streams and rivers that may in turn drain into freshwater lakes
• here they may have harmful effects on humans if the river of lake is a drinking source
• very high ion nitrate concentrations in drinking water can prevent efficient oxygen transport in babies and link to stomach cancer in humans is suggested
• leached nitrate ions are also harmful to the environment as they can cause eutrophication

Question 3

what is eutrophication?

Answer 3

• process by which nutrient concentrations increase in water bodies
• it is a natural process that occurs mostly in freshwater lakes and lower reaches of rivers

Question 4

eutrophication consists of the following sequence of events:

Answer 4

1- in most lakes and rivers,there is naturally a very low concentration of nitrates and so nitrate ions are a limiting factor for plant and algal growth
2- as nitrate concentration increases as a result of leaching it ceases to be a limiting factor for growth of algae and plants whose populations both grow
3- as algae mostly grow at the surface,the upper layers of water become densely populated with algae
4- this dense surface layer of algae absorbs light and prevents it from penetrating to lower depths
5- light then becomes the limiting factor for the growth of plants and algae at lower depths and they die
6- the lack of dead plants and algae is no longer a limiting factor for growth of saprobiontic bacteria so these populations grow using dead algae as a food source
7- saprobiontic bacteria require oxygen for their respiration = increase demand for it
8- conc of oxygen in water reduces and nitrates are reduced from decaying organisms
9-oxygen then becomes limiting factor for population of aerobic organisms such as fish which ultimately die as oxygen used up altogether
10- without the aerobic organisms, now less competition for anaerobic organisms whose population now rise
11- anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes such as HYDROGEN SULPHIDE which makes the water putrid