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Presentation on theme: "THE NITROGEN CYCLE."— Presentation transcript:


2 Warm Up How much of the atmosphere is made up of Nitrogen?
Why do plants and animals need nitrogen? Read “The nitrogen cycle” and answer questions 1-10

3 What is Nitrogen? -the most abundant element in the earths atmosphere (78% of the atmosphere) -can’t be absorbed by animals/plants until it is converted by the nitrogen cycle -needed to make protein


5 Nitrogen Fixation-converting nitrogen to ammonia.
Bacteria along with electrical storms can help convert Nitrogen gas (N2) into ammonia (NH4+) Lightning provides sufficient energy to split the nitrogen atoms of nitrogen gas Forming oxides of nitrogen NOx and NO2 © 2008 Paul Billiet ODWS

6 Nitrification-Ammonia to Nitrates by Bacteria
This involves two oxidation processes The ammonia produced by ammonification is first converted to nitrite (by bacteria): NH3 + 11/2O2  NO2- + H2O The nitrite is then converted to nitrate (by bacteria): NO3- + 1/2O2  NO3- The bacteria to do this are chemoautotrophs © 2008 Paul Billiet ODWS

7 Ammonification-Nitrogen to Ammonia by decomposition.
Nitrogen enters the soil through the decomposition of protein in dead organic matter Creates ammonia © 2008 Paul Billiet ODWS

8 Denitrification-Returning Nitrogen to the Atmosphere
Nitrates and nitrites can be used for their oxygen for bacteria once the oxygen is used.....Nitrogen (N2) is returned to atmosphere. 2NO3-  3O2 + N2 2NO2-  2O2 + N2 © 2008 Paul Billiet ODWS

9 Nitrogen from the atmosphere
Out gasing Atmospheric fixation Atmospheric Nitrogen 4 000 000 000 Gt Root uptake Nitrate NO3- Plant protein Soil organic nitrogen Biological fixation © 2008 Paul Billiet ODWS

10 Root nodules Alafalfa (Medicago sativa) USDA - ARS
University of Sydney

11 The nitrogen fixers Cyanobacteria are nitrogen fixers that also fix carbon (these are photosynthetic) Rhizobium bacteria are mutualistic with certain plant species e.g. Legumes They grow in root nodules Azotobacter are bacteria associated with the rooting zone (the rhizosphere) of plants in grasslands © 2008 Paul Billiet ODWS

12 The human impact Atmospheric Nitrogen Industrial fixation
Nitrate NO3- Atmospheric fixation Out gassing Plant protein Atmospheric Nitrogen Ammonium NH4+ Soil organic nitrogen Industrial fixation Biological fixation © 2008 Paul Billiet ODWS

13 Industrial N-Fixation
The Haber-Bosch Process N2 + 3H2  2NH3 High temperatures (500°C) High pressures (250 atmospheres) The energy require comes from burning fossil fuels (coal, gas or oil) Hydrogen is produced from natural gas (methane) or other hydrocarbon © 2008 Paul Billiet ODWS

14 The different sources of fixed nitrogen
Production / M tonnes a-1 Biological 175 Industrial 50 Internal Combustion 20 Atmospheric 10 © 2008 Paul Billiet ODWS

15 Eutrophication-Nitrogen into water.
Nitrogen finding its way into bodies of water Usually washed from draining soil When fertiliser is added to these soils it too will be washed out into water bodies This leads to a serious form of water pollution © 2008 Paul Billiet ODWS

16 Fertilisers washed into river or lake Sewage or other organic waste
Eutrophication Fertilisers washed into river or lake ALGAL BLOOM Rapid growth of algae Dead leaves New limiting factor imposes itself Sewage or other organic waste Death of algae Decomposers (bacteria) increase in numbers © 2008 Paul Billiet ODWS

17 Making things worse! Pollution from oil or detergents
Decomposers (bacteria) increase in numbers Pollution from oil or detergents Hot water from industry (Thermal pollution) Increased Biochemical Oxygen Demand (BOD) Reduction in dissolved O2 © 2008 Paul Billiet ODWS

18 The death of a lake Death/emigration of freshwater fauna
Reduction in dissolved O2 ANAEROBIC CONDITIONS Increased nitrite levels NO3-  NO2- Death/emigration of freshwater fauna Methaemoglobinaemia in infants Stomach cancer link (WHO limit for nitrates 10mg dm-3) © 2008 Paul Billiet ODWS

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