Biogeochemical Cycles Flashcards
What is the importance of biogeochemical cycles?
continual recycling means a small quantity of of material can support ecosystems over long time periods
What are the two main carbon cycles?
Give examples
Fast carbon cycle e.g. photosynthesis
Slow carbon cycle e.g. ground storage
What is the fast carbon cycle?
Where carbon is mainly cycled around living organisms and the biosphere
between 1,000 - 100,000 million metric tonnes move through the fast carbon cycle each year
What is the slow carbon cycle
carbon moves through rocks, soil, oceans and atmos through chem reactions and tectonic activity
taking between 100-200 million years
What are the reservoirs of the carbon cycle and nitrogen cycle?
Atmosphere
Hydrosphere
Lithosphere
Biosphere
What are the main chemical forms of carbon in:
a) the atmosphere
b) the hydrosphere
c) the lithosphere
d) the biosphere
a) gas - CO2, CH4, CO
b) Hydrogen carbonate ions, dissolved CO2
c) carbonaceous rocks e.g. limestone (mainly CaCO3), fossil fuels (mainly carbon and hydrocarbons)
d) carbs e.g. starch, cellulose
Proteins
Lipids e.g. veg oil, animal fat
What are the main processes of the carbon cycle?
Photosynthesis
Respiration
Food webs
Fossilisation
Combustion
What is photosynthesis?
- where light energy is captured by pigments e.g. chlorophyll
- converts low energy substances e.g. carbon dioxide and water into high energy substances e.g. carbohydrates
- carbs may then be converted into proteins/lipids
What is respiration?
The chemical reaction occurring within all living cells, which releases the energy from photosynthesis, which is then used to drive metabolic processes
What are the two types of respiration and explain
Aerobic - releases more energy and breaks down organic compounds more completely
Anaerobic - allows some organisms to survive/use food sources in oxygen-depleted env. Returns carbon to atmosphere as methane
What are food webs?
The combination of feeding relationships within an ecosystem
- carbs/proteins/lipids produced by plants are eaten by herbivores, which are eaten by carnivores…
What is fossilisation?
Give an example
The incomplete decomposition of dead organic matter under anaerobic conditions forming substances that form long term carbon stores e.g. ff
e.g. organisms with CaCO3 exoskeletons (corals, molluscs) fossilise into carbonaceous rocks such as limestone which contain most of the carbon in the lithosphere
What is combustion?
Give an example
The burning of organic materials releasing CO2,
e.g. forest and grassland fires started by lightning
How do humans change the carbon cycle?
Human activities unbalance the natural equilibria and changes carbon distribution in reservoirs
What changes do human bring to the carbon cycle?
Changes in:
- photosynthesis
- aerobic respiration
- anaerobic respiration
- carbonic acid conc in the sea
- methane/CO2 released by ff
- combustion
- biomass movements
How do humans change photosynthesis?
- Deforestation
- less carbon from atmos into biomass - Afforestation
- more carbon from atmos into biomass - Toxic material pollution
- kills phytoplankton which decreases CO2 absorption
- less stored in marine sed when pp dies
- so less CO2 dissolved to replace it in equilibria
- increases atmos conc - CC reducing sea ice
- less CO2 absorbed by algae on sea ice bottom
- less C sinks in poo of algae eating krill
- less CO2 removed from atmos
How do humans change aerobic respiration?
PLOUGHING
- when soil orgs respire (bacteria, fungi), C in dead organic matter gradually releases as CO2
- ploughing aerates soil so increases O availability
- faster resp = less C in dead org matter, more in atmos
How do humans change anaerobic respiration?
Anaerobic env = no oxygen. Resp by soil orgs releases methane, which oxidises in the atmos to CO2
INCREASED AR ENV:
- padi fields (when flooded, oxygen content is depleted in the bulk soil)
- landfill sites
- anaerobic sed. in reservoirs
- livestock intestines (to break down complex carbs e.g cellulose in plants)
DECREASES AR ENV: (drained for housing/infr/agri)
- waterlogged fields
- marshlands
- peat bogs
How do humans change the carbonic acid conc in the sea?
CC:
- if temps rise, more CO2 dissolves and dissociates
- CO2 goes to hydrogen carbonate and H+ ions
= more acidic
How do humans change methane releases from fossil fuels?
gas venting and leaks from ff infrastructure/wells goes into atmos during extraction
How do humans change combustion?
combustion of ff/wood releases CO2 into atmos
INCREASED:
- manufacturing (e.g. demand for cars, increased pop)
- consumerism (e.g. more deforestation for material)
- military testing/war (e.g. UKR, Gaza)
DECREASED:
- demand for electric cars (no ff)
- increased recycling/alternatives/protections/mindset (e.g. FSC)
How do humans change biomass movements?
INDIRECT:
- addition of compost/mulch to improve soil fertility
- deforestation/crop harvesting = less soil organic matter, soil erosion
- movement of biomass into sea when sewage is discharged
- movement of marine biomass into terrestrial system (fishing, aquaculture)
How can the carbon cycle be sustainably managed?
- Conservation of biomass stores
- alternatives to ff
- carbon sequestration
- Carbon Capture and Storage
What is CCS?
capturing CO2 at emission sources, transporting it, then storing/burying it in a suitable deep, underground location
- removal of CO2 directly/indirectly from the atmos
Give some solar power stats
- 4.9% UK’s total energy gen
- most widely used alternative energy source worldwide
- solar energy extracted using PV cells
- used for light and heat e.g. solar water heating
How do photovoltaic cells work?
- cells made from silicon material which absorbs light, causing electrons to move
- generates a DC
- each PV cell = small, so they are mounted into a module which is further grouped with other modules into an array
- the power generated is used to charge cells or inverters and then onwards to power common electrical appliances
How does solar thermal work for solar water heating?
solar panels used to trap energy then water circulating within the panels is warmed
- panels painted black to absorb heat in order to obtain the maximum energy from the sun
- using the hot water produced can reduce energy usage and elec bills
What percentage of the air is nitrogen?
78%
What state is nitrogen at RTP?
gas
What do living organisms need nitrogen for?
biological molecules:
- amino acids (protein building blocks)
- structure of DNA (nucleic acid base)
What are the main chemical forms of nitrogen in:
a) the atmosphere
b) the hydrosphere
c) the lithosphere
d) the biosphere
a) nitrogen gas (N2)
oxides of nitrogen (NOx)
b) dissolved nitrates and ammonium ions
c) Soil: ammonium compounds, nitrites, nitrates
Rocks: minerals containing nitrogen
d) Living orgs: DNA, proteins (cell membrane, hormones, enzymes)
Dead organic matter: proteins, which release ammonium compounds as they decompose
What are the main processes in the nitrogen cycle?
Fixation
Ammonification
Nitrification
Denitrification
Ionisation
Decomposition
Food chains
Leaching
Root absorption
Why is it unhelpful that nitrogen is a gas in the atmosphere?
most orgs cannot use this form because N has is inert so does not readily undergo chem reactions
How do plants get their nitrogen?
must incorporate nitrogen in ‘fixed compounds’ e.g. nitrate ions, ammonia or ammonium
How do animals get nitrogen?
from digest, absorb and assimilate forms of nitrogen from their food and pass it up the food chain e.g. from plants or other animals that have eaten plants
What is ionisation?
where processes from ionising phenomena (e.g. lightning and meteor trails) provide the energy to break the N triple bond, allowing it to react and produce oxides of nitrogen
What is nitrogen fixation?
where some microorganisms can chemically reduce nitrogen to compounds such as ammonia
- N taken out of atmosphere and stored in the ground
e.g. lightning and root nodules of leguminous plants
How do legumes fixate nitrogen?
LEGUMES: have N-fixing bacteria called rhizobium that form a symbiotic relationship with root nodules. They convert N gas into ammonia that undergoes nitrification into nitrites then nitrates that plants use to make proteins
e.g. peas, beans, clover
Where can bacteria (not rhisobium) that fixate nitrogen be found?
free living in soils
- AZOTOBACTER
How does rhizobium fixate nitrogen?
- contains an enzyme called nitrogenase
- converts N and H to ammonia
- used to make AA which the legume can then use to make proteins in return for supplying the bacteria with carbohydrates
What is decomposition? (NITROGEN CYCLE)
Where some free living bacteria and fungi break down animal and plant proteins with the nitrogenous waste released into the soil as a form of ammonium
What is the process before, during and after decomposition? (NITROGEN CYCLE)
- proteins made by plants enter and pass through food chain
- at each trophic level, metabolism produces organic nitrogen compounds that return to the env mainly in excretions
- the final beneficiaries of these materials are microorganisms of decay which break down the molecules in excretions and dead organisms into ammonia, a form of ammonium
basically: root absorption, food chain, excretions, decomposition
What is nitrification?
oxidation of ammonium ions to nitrites, then nitrates, by nitrifying bacteria in the soil (free living and aerobic)
How does nitrification work? (bacteria)
Nitrosomonas convert ammonium to nitrites
Nitrobacter convert nitrites to nitrates
BASICALLY: ammonium, bacteria, nitrites, nitrates, roots
What is denitrification?
the chemical reduction of nitrates in soil into nitrogen and NOx gases, by anaerobic denitrifying bacteria, decreasing soil fertility
How does denitrifictaion work?
denitrifying bacteria in soil or anaerobic aquatic sediments e.g. pseudomonas use nitrates as an alternative to oxygen for the final electron acceptor in their respiration
when they convert the nitrate back into nitrogen gas, it then gets released into the atmosphere
What is feeding along a food chain?
where nitrogen passes between organisms as amino acids and proteins in food
What is root absorption/assimilation? (NITROGEN CYCLE)
soluble ions such as nitrates and ammonium compounds are taken into plant roots
What is leaching?
loss of soluble ions such as nitrates from the surface layers of the soil as it is carried away by water
- often carried into water bodies, where it acts as nutrients for aquatic plants and algae - EUTROPHICATION
What is the difference between fixation, decomposition, nitrification and denitrification?
fixation, decomposition, nitrification - remove N from atmos, pass it through ecosystems
denitrification - reduces nitrates to N gas, thus replenishing atmos, closing the N cycle
What is ammonification?
Where amino groups in proteins are released as ammonium ions by the actions of bacteria, fungi and detritivores as they decompose dead organic matter
What are the human actions having an impact on the nitrogen cycle?
The Haber process
Agriculture
Pollution/ff emissions
How does the Haber process have an impact on the nitrogen cycle?
- making ammonia from N and H using iron catalyst at high temp and pressure
- artificial fixation of N to ammonia requires loads of energy - ff=unsustainable
- ammonia can then be converted to nitrates
- main purpose is for fertilisers - more N out of atmosphere, more N in soil
How does the Haber process work?
combines N from air with H derived from mainly natural gas (methane) into ammonia
equal volumes of gas contains equal numbers of molecules
N2+3H2 = 2NH3
- N2 and H2 are fed in
- compressor @ 200 atm
- reaction: iron catalyst @ 450 degrees
- cooling chamber: NH3 is cooled to liquify the gas and unreacted N2 and H2 are cycled back into the compressor
How does agriculture have an impact on the nitrogen cycle?
- nitrate fertiliser use increases leaching and eutrophication problems if applied near a river or before heavy rain
- draining fields makes soil conditions aerobic so there are more nitrifying bacteria, so less N in the atmos due to decreased denitrification
- ploughing = soil disturbance = increased rate of decomposition of dead organic matter which releases more NOx into the atmos
- leguminous plants (peas, beans, clover) may be grown to increase soil nitrogen compound level which other crops can then absorb = less N in atmos
How does pollution have an impact on the nitrogen cycle?
- NOx released into the atmos by combustion, produces acid rain (nitric acids) that affects pH of soils and solubility of N. Some ecosystems need low N content to survive and excess nitrates can lower the species diversity
- acid rain increases the quantity of nitrates washed into the soils by rain (plus leaching)
What are the problems with NOx fossil fuel pollution?
- MOBILE: can be transported long distances on prevailing winds
- SMOG: ground level ozone from NOx and Volatile Organic Compounds (VOCs)
- damage to lungs, veg, crops - ACID RAIN: damages forests, buildings, water sources
- VISIBILITY: Nitrates and Nitrites block light and reduce visibility (e.g. increased car crashes)
- GLOBAL WARMING: N2O (nitrous oxide)= 300x more damaging than CO2
- PARTICLES: NOx reacts to form acid vapour and particles, penetrates lungs = emphysema, bronchitis, respiratory disease
What is eutrophication?
- increased rapid algal growth in water bodies due to increased nutrient levels
- biological waste may be washed into water bodies or dumped there
- ammonium compounds converted to nitrites and nitrates which cause the algal growth
How does eutrophication work?
- nutrients wash in
- rapid growth and proliferation of algae and phytoplankton
- block light so plants cannot photosynthesise (but the algae can be a food source)
- decompose: produce lots of CO2 leading to acidification, which lowers pH
- the decomposers decomposing them use lots of O2 so there is a drop in O2
- plants and animals die of hypoxia (lack of oxygen)
How can we sustainably manage the nitrogen cycle?
Control of combustion processes
Control of NOx releases
Management of biological wastes
Organic fertilisers
Management of soil processes
What are the chemical symbols for:
a) ammonia
b) ammonium
c) nitrites
d) nitrates
e) nitrous oxide
f) oxides of nitrogen
a) NH3
b) NH4+
c) NO2-
d) NO3-
e) N2O
f) NOx
Give some nitrogen fertiliser stats
- 800% increase in nitrogen fertiliser use from 1960-2000
- human activities contribute to twice as much terrestrial N fixation as natural sources and provides about 45% of the total biological useful N produced annually on Earth
- 1/4 all global food produced is wasted along the supply chain - excessive use of nitrogen fertilisers for food that’s never eaten
- as a component of fertiliser, N helps feed around 1/2 world’s pop
- N fertiliser prices rising, threats to food security
- NOx = 300x warming potential of CO2
Why is management of the nitrogen cycle so complex?
We need to balance food production with reducing CC. NOx emissions = 300x warming potential of CO2 but we need fertilisers to beat food insecurity
What is the importance of phosphorus?
BIOLOGICAL FUNCTIONS:
component of bones,
DNA,
RNA,
cell membrane,
proteins
Why is phosphorus a limiting factor on biological processes?
most P compounds have low solubility and there is no P gaseous reserve, meaning it is not biologically available
Where is the main reserve of phosphorus?
solid (particulate) P in Earth’s crust/phosphate rocks (sedimentary rocks) and deep sea sediments
What form is phosphorus mostly found in?
phosphate ions (PO4 3-) aka orthophosphate
- inorganic and biologically available to plants
How does the phosphorus cycle work?
- phosphate compounds found in sed. rocks
- rocks weathers - phosphorus slowly leaches into surface water/soils
- phosphate compounds in soils taken up by plant roots. P conc in soil = low, so plants develop symbiotic relationships with mycorrhizal fungi which extend hyphae into soil to enhance P uptake
- animals eat plants, get the P
- When plants/animals excrete/die, P taken up by detritivores (e.g. beetles, earthworms) and returns to the soil
- P compounds may also be carried in surface runoff to rivers, lakes, oceans. P = not very soluble in water, so binds tightly to molecules in soils and reaches water by travelling in runoff with eroded soil particles
- P compounds from water bodies/bio wastes of marine orgs sink to sea floor, forming sedimentary layers
- over long periods of time, P-containing sedimentary rock is uplifted to the land. Process very slow: average phosphate ion has oceanic residence time of 20,000-100,000 years
Why is it important that phosphorus is very efficiently recycled?
the amount released by rock is a very small fraction of the amount stored in biomass
How is the phosphorus cycle linked to the rock cycle?
phosphorus compounds in marine organisms are locked into the rock when dead organisms/waste sink to the sea floor then compact and cement into rock, then eventually gets uplifted into mountains, weathered, and the cycle starts again
a) What mineral is phosphorus found as?
b) What is the mineral commonly formed from?
c) Which three major rock types contain this mineral?
a) apatite, a type of calcium phosphate
b) remains of aquatic organisms
c) limestone, marble, mudstone
Why is the phosphorus cycle slower than carbon or nitrogen cycles?
- P compounds have low solubility
- no gaseous reserves/cycle
- sedimentation and erosion takes longer
- amount of P released by rocks is a very small fraction of the amount stored in biomass
a) What is the use of phosphorus in agriculture?
b) Why is phosphorus mined from rock for agriculture?
c) Why is mining rock for phosphorus agricultural supply unsustainable?
a) phosphorus fertilisers (e.g. ammonium phosphate)
b) because before apatite was mined, they strip mined guano deposits at the surface e.g. Nauru in Pacific Ocean (one of first sites) but now most large guano deposits have been fully exploited
c) because rock takes thousands of years to form so we are exploiting it faster than it replenishes and we will eventually run out
Which human activities impact the phosphorus cycle?
- deforestation e.g. rainforest
- fertiliser use and agricultural run off
- mining of phosphate rocks
How does deforestation impact the phosphorus cycle?
- rainforest ecosystems are supported through recycling of nutrients, with little/no nutrient reserves in soil
- as forest cut/burned (mainly for agriculture) nutrients originally stored in plants/rocks are quickly washed away by heavy rain, making the land unproductive, so more and more is chopped. Vicious cycle
- no roots means soil erosion, and also no assimilation so less P is available for the cycle
- recovery is affected by P availability in soil, if there is rapid rates of soil loss (e.g. wind and water erosion) it may prevent complete ecosystem recovery
How does fertiliser use and agricultural run off impact the phosphorus cycle?
- fertilisers mobilises P compounds into the env in more soluble forms, increasing crop production but also run off and eutrophication
- crops cannot absorb all fertiliser in soil, which leads to increases phosphate levels in waterways, excessive growth of algae, and eutrophication
- algae produce toxic compounds, and when they die, their decomp by decomps uses O2 which causes hypoxia for other aquatic orgs (see eutroph flashcard)
How does the mining of phosphate rocks impact the phosphorus cycle?
most phosphorus mined as apatite (calcium phosphate) then treated to produce ammonium phosphate which is more soluble, and the full exploitation of guano deposits means more and more rock is mined
What are the main processes in the phosphorus cycle?
- root absorption/assimilation
- decomposition
- sedimentation
- mountain building and weathering
What is root absorption/assimilation?
(PHOSPHORUS CYCLE)
- plant roots absorb the phosphates they will use in metabolic processes
- not effective at absorbing phosphates as there is a low P conc in the soils, so forms symbiotic relationship with mycorrhizal fungi
- MF have extensive fungal networks of hyphae in the soil with increases SA for absorption
What is decomposition? (PHOSPHORUS CYCLE)
The breakdown of phosphorylated proteins in dead org matter releases phosphates that are often made more soluble by soil microbes so they can be absorbed by plants. Alternatively, they get washed into waterways
What is sedimentation and how does it affect the phosphorus cycle?
Give an example
- where the P in sediments and particles settle on the seabed
- P in orgs that die and become incorporated into sediments may no longer be available to other orgs
e.g. plankton dies, sinks to sea floor. This reduces productivity of surface waters of oceans because P availability is often a limiting factor
What is mountain building and weathering and how does it affect the phosphorus cycle?
- where continental drift and uplift forms new mountain ranges and breakdown of rocks in situ (weathering) releases phosphates
- processes that mobilise phosphates and make it available to living orgs are often slow, so the P in marine sediments may not become available until the processes above happen
What methods can we use to sustainably manage the phosphorus cycle?
- Selective breeding/genetic engineering of crops
- improved farming practises
- biological fertilisers
How can selective breeding/crop engineering be used to improve sustainability of agricultural phosphate usage?
- some plants have evolved to adapt to P shortage: by identifying the genes associated with phosphorus efficiency (PE) it informs the development of engineering strategies in improved PE in P limited soils
- engineer root symbiosis with mycorrhizal fungi for inorganic phosphate (Pi) acquisition, or enhance Pi uptake per root length
(increases efficiency of P absorption by crops)
What improved farming practises can be used to sustainably manage the phosphorus cycle?
- Riparian buffers
- Subsurface injection
- Timing of fertiliser application
- Right amount of fertiliser application
What are riparian buffers and how do they sustainably manage the phosphorus cycle?
- vegetated areas next to waterways that protect water quality, flood control, erosion and wildlife
- they trap particulate nutrients and takes up some P, reducing runoff: reduced eutrophication, makes more P organically available, reduces need for more fertiliser
How do subsurface injections help sustainably manage the phosphorus cycle?
- injecting fertiliser/manure below the surface reduces runoff because it can go straight to the roots
How can the timing of fertiliser application sustainably manage the phosphorus cycle?
- maximises uptake
- reduces runoff
- reduces leaching
- reduces gaseous losses
How can the right amount of fertiliser applies sustainably manage the phosphorus cycle?
- by testing the soil, plants and manure to determine the optimum fertiliser amount, it minimises the excess that will be runoff or get leached and reduces the amount needed to be mined
How can the use of biological fertilisers sustainably manage the phosphorus cycle?
- it maintains P nutrient availability without needing more to be mined, and more can be recycled quicker and more efficiently
