[13.5] environmental issues of fertilisers

Question 1

what are 3 environmental issues concerning use of nitrogen-containing fertilisers?

Answer 1

1. reduced species diversity
2. leaching
3. eutrophication

Question 2

how do nitrogen-containing fertilisers lead to reduced species diversity?

Answer 2

• nitrogen-rich soils favour the growth of rapidly growing species (eg. grasses, nettles)
• they out-compete many species, which die as a result
• some communities only survive when soil nitrogen concs are low enough to allow other species to compete with the grasses

Question 3

what is leaching?

Answer 3

the process by which nutrients are removed from the soil

Question 4

why is leaching an issue?

Answer 4

• rainwater will dissolve soluble nutrients eg. NO₃⁻ and carry them deep into the soil, eventually beyond the reach of plant roots
• leached NO₃⁻ will find their way into watercourses eg. streams and rivers, that may drain into freshwater lakes
• harmful effect on humans if river or lake is a source of drinking water
• leached NO₃⁻ are also harmful to the environment as they can cause eutrophication

Question 5

what is the effect of very high nitrate ion concentrations in drinking water for people?

Answer 5

• prevents efficient oxygen transport in babies
• link to stomach cancer in humans has been suggested

Question 6

what is eutrophication?

Answer 6

process by which nutrient concentrations increase in bodies of water

Question 7

what is eutrophication caused by?

Answer 7

• mainly leaching of artificial fertilisers into watercourses
• organic manures, animal slurry, human sewage, ploughing old grassland can also contribute
• natural process that occurs mostly in freshwater lakes and lower reaches of rivers

Question 8

describe the process of eutrophication

LF = limiting factor, P&A = plants and algae, ARO = aerobic organism, ANO = anaerobic organism, saprobiontic bacteria = SB, decaying organisms = DO

Answer 8

1. most watercourses have ⭣ [NO₃⁻], LF for P&A growth
2. [NO₃)]⁻ ⭡ due to leaching, now ✗ LF for P&A growth. P&A pops ⭡
3. algae mostly grow at surface, ⭡ layers = densely populated with A (algal bloom, AB)
4. AB absorbs light. prevents it penetrating to ⭣ depths
5. light = LF 4 P&A at ⭣ depths. they die
6. lack of dead P&A no longer LF for growth of SB. SB pops ⭡; dead O = food
7. SB need O₂ for resp, ⭡ demand
8. [O₂] in water ⭣, NO₃⁻ released from DO
9. O₂ = LF for ARO eg. fish. die when all O₂ used up
10. no ARO so ⭣ comp for ANO. ANO pops ⭡
11. ANO further decompose dead material, releasing ⭡ NO₃⁻. water = putrid