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
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:
This has caused the planet to warm like a greenhouse, since fossil fuels were used as fuel (coal, then oil and natural gas):
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
- nitrogen fixing bacteria (often along roots like in bean plants) fix nitrogen gas (N2) into ammonia (NH3)
- this is converted into ammonium (NH4) which plants can use
Abiotic (non living) process:
- lightning or fires have enough energy to combine N2 with O2, making NO3
- NO3 is carried to the ground with rain (the rain smell)
- 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")
- Ammonium (NH4) converts to nitrite (NO2) (look up sodium nitrite and what is is used for)
- NO2 converts to NO3 (nitrate) (plants can use this)
- commercial fertilizers are something with NO3, like NH4NO3, ammonium nitrate (a potent explosive: Beirut port explosion)
Ammonification is when dead organisms return this NH4 back into the ecosystem through denitrification:
NO3 ->N2O->N2 gas
Summary:
- N2 gas in the air fixed by organisms into ammonia (NH3)
- Ammonia (NH3)converts into ammonium (NH4)
- ammonium (NH4) converts into nitrite (NO2)
- Nitrite (NO2) converts to nitrate (NO3)
so:
N2->NH3->HN4->NO2-NO3 (nitrate)
remember: plants ate nitrate
Nitrogen is a limiting growth nutrient in ecosystems, excess nitrogen can cause algal blooms:
- Nitrogen causes algae to bloom
- Algae dies, falling to the bottom of the water body
- 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:
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:
- assimilation
- mineralization
- sedimentation (like sedimentary rocks)
- uplift
- weathering (erosion)
Very little P is found in rivers, so it is a limiting nutrient (eutrophication)
Algal Bloom:
Dead zone, from watershed:
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)
Note what drives this entire cycle is solar energy...
Games to try:
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