ESS W2 L2 biogeochemistry

biogeochemistry: carbon and nutrient cycles

Biogeochemistry:

•     How the biosphere functions

• Life support systems of the planet

• Biological, geological, and chemical processes cycling elements through the earth system

Biogeochemical cycles:

• carbon cycle

• nitrogen cycle

• phosphorous cycle

The carbon cycle:

•    Left – living short term

• Right – long term, non-living

• Processes within carbon cycle happen on these different time scale

living short term carbon cycle

• Short term living part is photosynthesis

• Plants draw co2 out of atmosphere and convert into sugars – glucose, carbohydrates. Also oxygen

contemporary short term carbon cycle

• Heterotrophs produce carbon dioxide and water which is needed by autotrophs

•   Light/ solar energy converted by chloroplasts/ chlorophyll into chemical energy by ATP. Take carbon dioxide and water and convert it into glucose and oxygen

photosynthesis

Enzyme called rubisco draws in carbon dioxide into plant biomass. Essential in converting it into sugar

ATP - ADP cycle powering life

•   Photosynthesis

• ATP – three phosphate groups. Energy gets stored in bond between second and third group. When that bond is broken, energy gets released

• Atp becomes adp.

• They cycle through going between atp and adp as they pick up a phosphate then bond is broken

•   P = phosphorous

Contemporary organic C cycle:

• The biosphere is estimated to contain 3170 gigaton (GT)s of carbon, broken down into:

  • Soils = 2500 GT

  •   Living plants and animals – 560 GT

  • Atmosphere = 800 GT

• In the atmosphere, there are 100,000s GT of O₂ in the atmosphere

• For every molecule of CO₂ fixed one molecule of O₂ is released

  •   6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

• So where is the rest of the carbon if not in the biosphere?

long term carbon cycle

  The long term carbon cycle is important to answer it – explains movement of carbon into geosphere

non living carbon cycle

• Carbon dioxide in the atmosphere is released by volcanoes (terrestrial and along ocean ridges on the sea floor – where it is spreading) releasing CO2

• From lithosphere/ geosphere

• Chemical weathering pulls down carbon from the atmosphere to the lithosphere. Atmospheric carbon reacts with water. Forms a weak acid (carbonic acid) that dissolves rocks into bicarbonates. Transport to oceans where marine organisms use calcium carbonate to make shells.

• Most of the calcium carbonate in oceans is made by calcifying (shell building) organisms (corals, plankton like coccolithophores).

• When they die, these organisms sink to the seafloor, where over time, layers of shells and sediments become compressed together and turn to rock, capturing carbon in the bedrock (limestones, or marble – a form of metamorphic limestone).

• The eruption of volcanoes and seafloor spreading releases carbon dioxide and the process starts again. 

Peatlands: terrestrial C accumulation and burial:

•   “Peatlands store vast quantities of carbon – 'locking in' an estimated 3.2 billion tonnes in the UK alone.

• Where peat continues to form this helps to offset the effects of human activities (such as fossil fuel burning) that are raising CO2 levels in the atmosphere, leading to climate change.”

• Peats from ~ 1m / 1000 years

• Carbon sinks due to waterlogged conditions and little oxygen. Also quite acidic where organic matter doesn’t decompose

•   Help keep carbon locked in geosphere

Geosphere: carbon storage:

•   20 % of carbon-containing rock contains carbon from living organisms (organic carbon) that have deposited in layers of sediments.

•    Over millions of years, heat and pressure will result in the formation of sedimentary rocks, e.g. shales,

• However, where dead organic carbon accumulates faster than it can decay, carbon-rich layers of oil, natural gas or coal form.

Terrestrial carbon burial: coal:

•    Over time plant matter accumulates

•   E.g. from peat

• Gets compressed and heated up

Marine carbon burial: oil and gas:

• occurs in ocean – not a terrestrial process

• Tiny organisms – phytoplankton - autotrophic

• aquatic plants and animals die and are buried on the ocean floor by layers of sand and silt

• layers of sediment are deposited above and the pressure and heat causes compaction of the remains

• the remains become oil and gas which are forced out of porous rock to form deposits which we drill for

Oil and gas:

•   Marine sediments: zoo and phytoplankton - buried under anoxic (no oxygen) conditions.

• Sedimentation increased the pressure and temperature

•   Organic matter - converted into oil & gas

• Get buried under anoxic conditions

•    Sedimentation increased the pressure and temperature

• Organic matter – converted into oil and gas

Burial of organic matter:

• Huge amounts of carbon in these sediments (100,000s of giga tonnes)

• Burying the carbon that became fossil fuels was key to advanced animal life on Earth as allowed oxygen to build up in the atmosphere.

• Without burial, decomposition would have released almost all the carbon as CO₂ and consumed the oxygen in the atmosphere

•    Link between biological and geological processes is key = Biogeochemistry

Human influence on the carbon cycle:

•   Humans releasing carbon thats been locked away for millennia in geosphere and releasing it into the atmosphere.

• Causes an imbalance in carbon cycle

when last uk coal fired power station closed

30^th September 2024

CO2 and global warming:

•   Known as the Hockey stick graph

•     Shows long-term cooling trend interrupted by rapid rise in temperature during the 20^th century

• Human –produced green houses gases (including CO2) are causing global warming

•   Change in global surface temperature over time.

• Data from 1902-1998 – observed data

• Before that – reconstructed from proxy records: e.g., ice cores, tree rings

How is global warming impacting the biosphere:

-              Some examples:

•    Extinction- rates higher than natural, particularly impacting vulnerable species (limited range or isolated populations).

•    Loss of habitat

• Ecosystem changes (e.g,. ocean acidification)

• Range shifts - forcing plants and animals to migrate to escape temperature increases.

• Timings of bird migration and caterpillar hatchings not working properly due to warming but not having resources available for offspring

 

Nitrogen cycle:

 Key nutrients for life:

• Nitrogen

  • Proteins, nucleic acids (DNA)

• Phosphorous

  • Nucleic acids, ATP, membranes

• Potassium

  • Osmosis, transport

• Sulphur

  • Proteins

• Calcium

  •   Membrane, and enzyme function

• Magnesium

  • Chlorophyll

•    Iron

  • Chlorophyll synthesis, oxygen transport

•   Others:

  •   Sodium, manganese, boron, copper, zinc, molybdenum

nitrogen gas abundance

  Most abundant gas in atmosphere – 78% air

nitrogen triple bond

• In atmospheric form – 2 nitrogen atoms bonded together – covalent bond

•     Very strong bond

•   Plants and animals can’t break and use it

Nitrogen cycle: soil microorganisms:

• Conversion can only happen by nitrogen fixing bacteria (in soil)

•   Bacteria take nitrogen from atmosphere and fix it into soil making it available to plants

• Atmospheric nitrogen into ammonia

• Ammonia can pick up extra nitrogen atoms in soil to make ammonium

• Ammonium taken up by plants to make dna etc.

•   Lightning and wildfires play important role in nitrogen cycle as the energy  can break apart the atmospheric nitrogen bonds.

ammonium in nitrogen cycle

• Ammonium is positively charged (soil is negatively charged)

•   They are attracted to soil particles so are retained din soil – not vert mobile

• Nitrate is negatively charged – repelled by soil particles – is highly soluble – leeches out of soils

  • As they aren’t retained well humans add them back in

Human activity and the N cycle:

•   Human activity is having a major impact on the nitrogen cycle: fertilizers

• We can now make liquid nitrogen (nitrate) from N2 (gaseous nitrogen)

• Nitrogen fertiliser (using chemicals using the Haber process)

• Has become an important part of the N cycle

• 80% of the nitrogen in your body comes from an artificial fertiliser source.

The Haber process:

Nitrogen accumulation in oceans:

• quantities of nitrogen

• Accumulates in soils/ lakes

Eutrophication:

•   Causes oceans to acidify

• Nature based solution using oyster reefs to remove nitrogen from oceans

Acid rain:

•       1 - Emissions of SO2 and NOx are released into the air

• 2 - pollutants are transformed into acid particles that may be transported long distances

•    3- These acid particles then fall to the earth as wet and dry deposition (dust, rain, snow, etc.)

•    4 - may cause harmful effects on soil, forests, streams, and lakes.

Phosphorous cycle:

 Phosphorous: PO₃^-3

•   Essential in living organisms:

• phospholipids in cell membranes

•   DNA and RNA

• ATP, NADPH

Phosphorous cycle: the slow cycle:

• Units = teragrams = 10¹² g P yr^-1

•   Phosphorous is a very slow cycle

Saharan dust and the phosphorous cycle:

•     Dust blown off the Sahara crosses the Atlantic and fertilises the Amazon – where amazon gets its phosphorous from

• The most productive ecosystem on the planet is dependent on one of the least productive for key nutrients

• Amazon rainforest – phosphorous poor – doesn’t have that bedrock.  Heavy rainfall means that P is lost rapidly

Nitrogen versus phosphorous:

Similarities

•    Effective recycling within terrestrial ecosystems

• Transport to oceans through rivers

• Human addition through fertilizers

•    Long-term burial in sediments

Nitrogen versus phosphorous: differences

•   No gaseous phase in phosphorus cycle

•   Main inputs differ

•    Biological nitrogen fixation

• Geological rock weathering

What happens if all the phosphorous is mined:

 Summary:

•     Biogeochemistry = study of the biological, geological and chemical processes cycling elements through the Earth System

• Carbon, nitrogen and phosphorus cycles are essential to life on Earth

• All cycles are being affected by human activity