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Biogeochemical Cycles - Coggle Diagram
Biogeochemical Cycles
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- The long-term carbon cycles
- Early Earth – 4 Billion years ago
- Then 10% CO2 atmosphere now only 0.04 %
- Came from volcanoes
- On Venus, this led to a runaway greenhouse
- On earth it has not – life evolved, photosynthesis has saved the earth from a runaway greenhouse effect
- we got lucky, temp and shell forming animals
- starting temp on venus was a little too high
- CO2 is taken from the atmosphere by weathering if temps are < 60 degrees
- Temperature on earth has stayed relatively stable
- Without the evolution of life, earth would’ve been like Venus, and we would have been a greenhouse world
- carbon cycling in the ocean
- Co2 in ocean surface waters exchanges occurs in a dynamic equilibrium- carbon solubility series
- C is taken out of ocean to rock storage by 2 processes
- Organic rainout
- Co2 initially gained from photosynthesis is about 20% of C stored since the formation of the earth’s atmosphere 4 billion years ago
- Once carbonates formed things really took off
- 80% of carbon removed from the earth’s surface has been removed by calcium carbonate- shell forming organisms
- Remaining 20% removed by photosynthesis
- main pathway of carbon
- stored in most common rocks worldwide
- lime stone
- formed mostly in the ocean from the shells/structures of organisms
- Banded ironstone and snowball earth
- Banded iron formations result from oxygenation of oceans by photosynthesis
- Caused a major drop in CO2
- Resulted in precipitation of iron from dissolved iron in seawater
- 750-625 MYA
- Snowball earth – continental glaciers reached the tropics - small area of the earth that want glaciated
- summary
- Calcium carbonate precipitates as a direct consequence of biological activity
- Without biological activity carbon would increase = runaway green house
- Photosynthesis and calcite shell building are key
- What is happening geologically
- Global climates have cooled dramatically
- No revolution in photosynthesis or shell building in the last 50 million years so something else is driving the cooling
silicate erosion is the removal of C from the atmosphere
- uplift of Himalayas
- mountain building removes CO2 and has saved the earth from runaway greenhouse
- radiocarbon
- carbon 14
- radioactive
- very useful to us
- Incoming high energy particles strike
Nitrogen in the upper atmosphere
- Convert Nitrogen to Carbon by swapping
a neutron for a proton
- C-14 is taken up by organisms and surface
Water – contains CO2
- When organisms die they no longer breathe and their carbon 14
begins to breakdown. No new C-14 is absorbed.
- C-14 breaks down to N-14 by spontaneous decay reaction
- carbon 14
- half life of 5730 years, 50% of C14 has broken down to N14 after 5730 years
- Every 5730 years the amount of radiocarbon halves
- The amount of radiocarbon left in an organism becomes too small to measure after about 10-12 half-lives so radiocarbon can be used to date materials that contain carbon as 50,000 to 70,000 years old
- It is really rare – 1 atom of C-14 per 1012 atoms of Carbon
- water also contains carbon
- as dissolved organic carbon and dissolved inorganic carbon and particulate carbon
- water has the age of the carbon in it
- small water bodies have the same age as the atmosphere (0years)
- large water bodies have residual age from the carbon in the water
- average age of sea water is 400 years old
- global thermohaline circulation
- system for heat transfer from north Atlantic where there is surplus heat to the north pacific where there is a lot less heat
- also to the southern ocean
- warm salty water for cooler fresher water
- like a pump going around the planet
- 1500 years to move water from north Atlantic to north pacific
- Antarctic circumpolar current
- strongest current in the world
- very turbulent ocean
- nutrients upwelling from deeper ocean promote very active biological activity
- fix carbon trapped from atmosphere
- In the tropics the oceans are deserts
- Southern Ocean is very productive
- Co2 in the atmosphere is controlled by global circulation patterns
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- Atmospheric transport of carbon
- global atmosphere mixes over about a year
- CO2 released over the northern hemisphere is spread planet wide within 12 months – reverse of this for methane in nz
NITROGEN CYCLING
- nitrogen
- N is very common
- Hard to access for plants and animals
- Useable N occurs as- organic N, nitrate, ammonia
- Nitrogen gas is extremely stable – very hard for the bonds to be broken
- Critical for biological activity
- Plants won’t grow without accessible nitrogen
- Bacteria are critical for uptake and conversion of N to usable forms
- Huge human addition to global N cycle – critical
- Causes euthropication and effectively poisons waterways
- It is a major issue in Canterbury
- Available forms of nitrogen
- Nitrogen fixing bacteria convert N2 to NH3 ammonia
- N2 converted to N2O or NO3 by lightening
- Nitrogen fertilizers, urea, inorganic
- Legumes/pea family add nitrogen to the system and therefore increases the fertility of all plants
- Processes of N conversion
- Nitrogen fixation – conversion of N2 to an accessible form of N by biological activity
- Ammonification - chemical reaction in which NH2 groups are converted to ammonia/ammonium as an end product
- Nitrification – oxidation of ammonia to nitrite and then to nitrate - high oxygen environment needed
- Denitrification – reduction of nitrate and nitrite to gaseous forms of nitrogen
- Nitrogen is a necessary fertilizer
- N is critical but has side effects
- Eutrophication – over fertilising a water body- changing the biological activity
- Oxygen depletion – fish kills
- Altered transfer between trophic levels and components
- Autotrophic to heterotrophic
- Problems with nitrates
- Contamination of water
- Needed for enhanced grass growth, by product of animal activity
- Nz has set limit of synthetic N to be used from 2022
- Nitrogen cycling through soil/vegetations systems
- Conversion of N to usable forms is challenging
- Most ecological systems have their productivity limited by the availability of N or P
- Adding N to systems makes them much more productive
- Human addition of N to agricultural systems is huge.
- Pea family used as a rotation crop, which allows nitrogen to be added to the system
- Nitrate contamination in canterbury
- Increased dairy farming
- Nitrate in the water
- Cattle
- Nitrate from farming enter groundwater and rivers
- Most rivers carried N to sea
- Discharge areas for shallow aquifers often contain high levels of N
- Wetlands, shallow lakes become eutrophied
MARINE NITROGEN CYCLING
- Multiple transformation processes
- Microbial mediation central to N cycling
- Can involve multiple different microbial species and or communities
- Some transitions are cyclic
- Relative function of different processes can lead to changes in production in the ecosystem
- Just like carbon N is transferred from surface to deep water
- Upwelling is important
- energy flow and biogeochemical cycling
- concentration of photosynthesis around the mouth of rivers
- due to the supply of nutrients coming in
- availability of nutrients in the surface water is highest around Antarctica and north pacific
- high productivity in these places
- surface ocean currents explain part of the pattern
- Nitrous oxide as a greenhouse gas and pollutant
- Total global emissions 47.5 Tg N
- 300 times more efficient as a greenhouse gas than CO2
- Mostly derived from automobiles, agriculture, and industry
- mercury
- Mercury (Hg) is toxic to life but present in low quantities everywhere
- Forms organic compounds
- Hg compounds can cause serious disease
- Global sources are industrial, nz mostly volcanic
- Metal – liquid at room temp (only metal that can do this)
- Earth’s crust contains 89nanograms per gram
- Soil – 60ng/g
- Seawater – 2-15ng/L
- Open water/freshwater – 0.5-3 ng/l
- Mercury is present in the atmosphere as an elemental gas
- Methylation of mercury
- Biomethylation process, microbially mediated
- Process occurs in sediments and soil
- Methylation and demethylation processes occurring
- Methylation processes are more important in aerobic environments. HgS and Hg0 formed in anaerobic environments
- Organic mercury compounds are more toxic than inorganic and elemental mercury
- Organic mercury can accumulate in the food chain
- Fish contain 80% methyl Hg and 95% is absorbed by the human body when eaten.
- Methyl mercury poisoning
- Loss of peripheral vision
- Pins and needles feelings in hands and feet and around mouth
- Lack of coordination
- Impairment of speech/hearing, walking
- Muscle weakness
- Chisso-minimata disease
- in extreme cases, insanity, paralysis, coma and death follow within weeks of the onset of symptoms.
- Mercury sources
- Occurs as gas in atmosphere
- Moves around the globe like air
- Mercury is diluted in the air
- Rained out of the atmosphere – getting mercury to the ground
- Mercury falling out of the atmosphere at very slow rate
- NZ mercury in fish advice
- Lake rotomahana due to the volcanic nature of the lake, the trout have a high mercury content and It is cautioned that consumption of high numbers of these trout should be avoided.
- Mercury from fish consumption: a global environmental issue
- children IQ effects
- adults cardiovascular effects
- Nz sources of Hg
- volcanic/geothermal sources dominate
- Global mercury production – fossil fuels, metal production, gold production
- China and India, very high mercury
- travels in the atmospheric circulation
- Human activity and Hg transport
- Hg mining goes back at least 4000 years in South America
- Romans and Chinese were mining Hg on an industrial scale by 2000 years ago
- Records are preserved in ice
cores and lake records.
- Massive up step in Hg after the industrial revolution
- UNEP Minimata Convention on Mercury (2013)
- No new Hg mining (old mines allowed to continue)
- • No manufacture of mercury added products (e.g. in batteries, lamps, thermometers) from 2020 (can be extended to 2025)
- Phase out of production of products that contain mercury
- Control of emissions from power
stations etc within 10 years