2.5 - carbon and nitrogen cycles, Harber process

biogeochemical cycles

processes that recycle nutrients and elements through the Earth's ecosystems so:

• the elements can continue to be available to living organisms

*finite resources must be cycled around ecosystems constantly is life is to be sustained

carbon cycle

processes through which carbon compounds are circulated in the environment

carbon stores

• organic (complex carbon molecules)

  • organisms in the biosphere

  • fossilized life forms

• inorganic (simple carbon molecules)

  • locked up/ fixed as

    • sedimentary rocks

    • fossil fuel

    • lime stone

  • locked up/ fixed as carbon in shells

  • soil

carbon flows

• transformations

  • respiration

  • photosynthesis

  • combustion

• transfers

  • feeding

  • defecation

  • death and decomposition

carbon sequestration

the process of capturing and storing atmospheric carbon dioxide to mitigate climate change.

agricultural systems and effect on carbon cycle

• no till farming

  • without ploughing soil is protected from erosion and organic matter loss

• cover cropping

  • planting 2nd crop to protect soil and the decay nourishing the 1st cash crop

• crop rotation

  • ensures no nutrient depletion

• agroforestry

  • planting trees in agricultural land to increase biomass and sequestrate CO₂ improving soil structure

• rice paddy fields

  • waterlogged rice fields release methane

human impacts on carbon cycle

• fossil fuels are carbon sinks and when burned become carbon sources releasing carbon into atmosphere

• agricultural systems acting as

  • carbon sinks

  • carbon sources

• oceanic carbon dynamics

human impacts on carbon cycle: agricultural systems

carbon sinks

• regenerative techniques

  • increase amount of organic matter in soil

carbon sources

• drainage of wetlands

• monoculture farming

• intensive tillage

• loss of organic matter

• reduced biodiversity

• increased release of carbon from soils

human impacts on carbon cycle: oceanic carbon dynamics

ocean acts as a carbon sink

• burning more fossil fuels releases more carbon at a faster rate than oceans can absorb

• warming temperatures due to climate change reduce ability to act as carbon sink

• increased carbon dissolved in oceans lowers the pH leading to ocean acidification

  • weakened shells

  • less diverse reef structure

solutions to human impacts on carbon cycle

• low carbon technologies

• reduction in fossil fuels burning

• reduction in soil disruption

• increasing reforestation

• carbon capture and sequestration

• ocean fertilization

  • adding compounds to stimulate phytoplankton growth that absorbs CO₂

carbon sinks

CO₂ intake > CO₂ release

• forests

• wetlands

• oceans

• soil and rocks

carbon stores

CO₂ intake ≈ CO₂ release

carbon sources

CO₂ intake < CO₂ release

• deforestation

• fossil fuel combustion

• industrial processes

nitrogen cycle

The process through which nitrogen is circling between its stores through being converted between its various chemical forms.

nitrogen stores

organic

• protein of living organisms

• DNA

• dead organic matter

inorganic

• atmosphere

  • N₂ gas

• soil and water

  • NH₃ ammonia

  • NO₂^- nitrites

  • NO₃^- nitrates

nitrogen flows

transfers

• mineral uptake

• consumption

• excretion

• death and decomposition

transformations

• nitrogen fixation

  • bacteria

  • lightning

• nitrification (nitrifying bacteria)

• denitrification

• ammonification

role of bacteria in nitrogen cycle

nitrogen fixation

• rhizobium bacteria coverts N₂ gas into ammonia NH₃

• then can be used by plants

• happens in:

  • soil

  • legumes with nitrogen-fixing bacteria

nitrification

• nitrifying bacteria convert ammonia NH₃ into nitrites NO₂^- and then into nitrates NO₃^-

• then plants absorb these nitrates through roots

denitrification

• denitrifying bacteria convert nitrates NO₃^- back into nitrogen gas N₂

• nitrogen gas returns to the atmosphere

• happens in:

  • anaerobic conditions (waterlogged soils)

decomposition/ ammonification

• decomposing bacteria breaks down the nitrogenous compounds into ammonium NH₄

• happens in: soil

mutualistic relationships and nitrogen fixation

plants cannot use nitrogen gas directly

• some plants such as legumes form relationships with nitrogen-fixing bacteria

  • competitive advantage in nitrogen-poor soils

human influences on nitrogen cycle

deforestation

• reduces amount of vegetation that can absorb nitrogen from soil for growth

  • leads to nitrogen leaching into water bodies

    • euthropication, algal blooms, dead zones

urbanisation

• sewage contains nitrogen

  • enters water bodies increasing nitrogen levels

• storm water runoff

• vehicle emission

  • reacts with water vapour and forms acid rain

aquaculture

• fish farms use fertilisers and antibiotics

  • pollute water bodies

    • excess nitrogen and ammonia

agriculture

• nitrogen fertilisers

  • increased rates of denitrification

  • leaching nitrate into groundwater

    • eutrophication

Haber process

A method to synthesize ammonia from nitrogen and hydrogen gases:

• under high temperature

• under high pressure

• in the presence of a catalyst

• primarily used in fertilizers.

N₂ + 3H₂ ⇌ 2NH₃

advantages of the Haber process

• increased crop yields

• reliable and large scale source of nitrogen fertilisers

• food security

• reduced land use

disadvantages of the Haber process

• environmental impact

  • runoff

  • eutrophication

  • dead zones → reduced biodiversity

• energy consumption

  • is reliant on fossil fuels and contributes to greenhouse gas emission

• pollution

  • fertiliser runoff

• soil health

  • over reliance on synthetic fertilisers can degrade soil health

    • disrupting natural nutrient cycles

    • reduced soil biodiversity

need for global collaboration in relation to nitrogen cycle

shared responsibility

• nitrogen pollution affects ecosystems and human health worldwide

agreements and policies

• existing frameworks provide ground for collaborations on nitrogen management

solutions to disrupted nitrogen cycle

• efficient fertiliser use

• promoting sustainable agriculture

  • crop rotation

  • precision farming

• reduced nitrogen emission

• promoting alternative nitrogen sources