# 24.11.06 earth science: biogeochemical cycles - Bio-geo-chemical cycles: bio=life, geo=earth, chemical=chemical - These are cycles as the go from some reservoir through the environment and back - These are known as sources and sinks - Often the reservoir will be the key to identifying the cycle ### Carbon cycle: air and living things

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Notice: - fast processes involve living things (you eat sugar, exhale carbon dioxide) - slow processes involve minerals, rocks and soil, hydrocarbons, and the oceans - photosynthesis: light energy creates chemical energy (e.g. sugar) - respiration: oxygen combines with sugar or other carbon fuel, releasing carbon dioxide and energy - chemosynthesis: same process only using heat instead of light, sulfur instead of oxygen (look on periodic table) - aerobic respiration: uses oxygen - anaerobic respiration: uses carbon based fuels without oxygen, much less efficient - carbon stored in the ocean as carbonate (H2CO3 or carbonic acid) - carbon stored in corals as CaCO3 (calcium carbonate) - carbon sediments can turn into fossil fuels (coal, oil, natural gas) with time, heat and pressure - steady state: sources and sinks are equal - fossil fuel extraction: combines with oxygen to form carbon dioxide and energy (reverse of photosynthesis) - released CO2 increases the heating of the earth:

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This has caused the planet to warm like a greenhouse, since fossil fuels were used as fuel (coal, then oil and natural gas):

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How fast is this changing?:

In 1990, the CO2 parts per million was increasing 0.4 ppm/year

In 2025, it is increasing 2.5 ppm per year

54% of the CO2 in the atmosphere has been added since ~1975

OMG...

A global temp increase of +1.5° by the year 2100 when you are ~80 years old WAS the warming target in 2000

+2° was the next one in 2010...

Latest predictions in 2025: +3° C and perhaps several meters of water rise

Last time the CO2 was this high: prehistoric water levels were 300m higher (Kamuela is at 800m).

### Nitrogen cycle: proteins - Nitrogen is in the air as N2, a diatomic molecule - We can't metabolize this as is, it needs to be incorporated into plants or animals we eat. - Plants cannot use nitrogen directly from the atmosphere, it has be in the form of nitrates ("plants ate nitrate") - Nitrogen goes through many changes to get from the air to food, usually involving oxygen, like nitrates (NO3) - Nitrogen fixation "fixes" nitrogen in the air into forms plants can use, either biotically (living things) or abiotically (not living things) - Nitrogen is the basis for amino acids, and therefore proteins in living thing

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Biotic process: Nitrogen fixing, most common

1. nitrogen fixing bacteria (often along roots like in bean plants) fix nitrogen gas (N2) into ammonia (NH3) 2. this is converted into ammonium (NH4) which plants can use

Abiotic (non living) process:

1. lightning or fires have enough energy to combine N2 with O2, making NO3 2. NO3 is carried to the ground with rain (the rain smell) 3. can also be done using the Haber process for chemical nitrate synthesis

Next step: Nitrification

Ammonium needs to be converted to Nitrate for plants ("plants ate nitrate")

1. Ammonium (NH4) converts to nitrite (NO2) (look up sodium nitrite and what is is used for) 2. NO2 converts to NO3 (nitrate) (plants can use this) 3. commercial fertilizers are something with NO3, like NH4NO3, ammonium nitrate (a potent explosive: [Beirut port explosion](https://www.youtube.com/watch?v=FnSr820S2Mk))

Ammonification is when dead organisms return this NH4 back into the ecosystem through denitrification:

NO3 ->N2O->N2 gas

Summary:

1. N2 gas in the air fixed by organisms into ammonia (NH3) 2. Ammonia (NH3)converts into ammonium (NH4) 3. ammonium (NH4) converts into nitrite (NO2) 4. Nitrite (NO2) converts to nitrate (NO3)

so:

N2->NH3->HN4->NO2-NO3 (nitrate)

remember: plants ate nitrate

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Nitrogen is a limiting growth nutrient in ecosystems, excess nitrogen can cause algal blooms:

1. Nitrogen causes algae to bloom 2. Algae dies, falling to the bottom of the water body 3. As it decays, it consumes the Oxygen from the water: dead zones

### Phosphorus cycle: energy

- Phosphorus is used as an energy molecule: AMP, ADP, ATP use P bonds to store energy (look these up) - P is also a key component in DNA and RNA - P is a limiting nutrient for plants, along with Nitrogen

Phosphorus cycle:

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Trick AP question: which cycle has no gas phase component?

Answer: Phosphorus, just between land and water

P is carried as dust from the Sahara to the US, and from the Gobi desert to Kauai (!) Usually in the form of phosphate (PO4) 5 processes:

1. assimilation 2. mineralization 3. sedimentation (like sedimentary rocks) 4. uplift 5. weathering (erosion)

Very little P is found in rivers, so it is a limiting nutrient (eutrophication)

Algal Bloom:

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Dead zone, from watershed:

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### Water (hydrologic) cycle: basis of life

- Transpiration: when water leaves plants through leaves (not the same as evaporation) - Evaporation: when water changes from liquid to gas phase (vapor) - Condensation: when vapor forms into drops (liquid) - Precipitation: when water drops fall from the sky (rain) - Evapotranspiration: a combination of sunlight, wind, humidity, temp, to increase transpiration from plants (known as EtO) - Runoff is when water moves across land into other bodies of water - Percolation is when it flows through soil, think of a coffee percolator (like in your soil lab) - Transit time: the time between when rain falls on the surface until it enters a stream or river body (recall #2 on your homework)

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Note what drives this entire cycle is solar energy...

Games to try:

[https://www.classtools.net/vortex/202201-VCk3Yb](https://www.classtools.net/vortex/202201-VCk3Yb)

[https://wordwall.net/resource/10488872/biology/eutrophication-mix-and-match](https://wordwall.net/resource/10488872/biology/eutrophication-mix-and-match)

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