Methane Lecture 2- Marc

Question 1

Define NETs

Answer 1

Negative Emission Technologies

Question 2

name sources of atmospheric methane ( answer lister in rough order of highest to lowest contribution)

Answer 2

natural wetlands
fossil fuels
ruminants- ie cows
flooded rice fields
landfills
biomass burning
termites
gas hydrates

Question 3

what is methanogenesis?

Answer 3

Methanogenesis is an anaerobic respiration that generates methane as the final product of metabolism.

Question 4

what percentage of intake in ruminants is lost as methane

Answer 4

2-12

Question 5

what is the pathway required to methanogenesis

Answer 5

polysaccharides
hydrolysis to monomers
acidogenesis to short chain volatile FA
H2, CO2 formate, OR with acetogensis acetate.
both Acetate and h2, co2 undergo methanogenesis to create
CH4 + CO2

Question 6

What performs methanogenesis

Answer 6

Performed by specialised archaea called methanogens (e.g. Methanosarcina, Methanococcus, Methanosaeta)

Question 7

most archaea are ( two choices)

Answer 7

hydrogenotrophic” (CO2 + 4H2 -> CH4 + 2H2O) or acetoclastic (CH3COOH -> CH4 + CO2)

Question 8

methanogenesis occurs where?

Answer 8

Occurs in flooded soils and other environments with a low redox potential (rumen, wastewater treatment plants, lake sediments)

Question 9

what is methane hydrate?

Answer 9

Methane hydrate (also known as clathrate) is a solid where methane is trapped in frozen (crystal) water. Composition is 4CH4·23H2O

Question 10

where is methane hydrate found?

Answer 10

Found mainly along continental shelves (1500-7000 PgC, IPCC 2013)

Also in permafrost (530 PgC)

Stable at low temperature and high pressure

Question 11

when is CH4 released?

Answer 11

if gas hydrates destabilise… i.e if sea level falls.
this is catastrophic, but considered unlikely

Question 12

what are Aerobic methanotrophs (methane oxidisers)

Answer 12

Their key enzyme is the methane monooxygenase
CH4 + O2 -> biomass + ATP

Question 13

is anaerobic methan oxidation possible?

Answer 13

sort of..
Methylomirabilis oxyfera make O2 from NO2-

Question 14

how much methane is in the atmosphere?

Answer 14

542-852 Tg year-1
Biological CH4 oxidation ~800 Tg y-1
Extra 17 Tg year-1 stays in atmosphere

Question 15

what is methanotrophy?

Answer 15

Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy.

Question 16

what is the equation for Aerobic methanotrophy (carbon cycle)

Answer 16

CH4+ 2O2 –> CO2 + 2H2O

Question 17

what is the equation for anaerobic methanotrophy

Answer 17

CH4 + SO (2-/4) OR NO3- –> CO2 + H2S or N2
numbers are end are small- high or low

Question 18

Do hydroelectric dams provide clean energy? what are the downfalls?

Answer 18

runoff- water entering reservoir adds decaying plant matter
water level changes- plants grow on banks. then die when level rises
plankton and leafy plants- release gas as they decay
diffusion- gases released from dying plants and soil
degassing- pressure change when water is released frees gases from the water
flood plants + soil- decay occurs after reservoir is first filled

Question 19

Name the sites you might see during thawing permafrost : TKL, ALD, RTS, GTK

Answer 19

TKL, thermokarst lakes
ALD, active layer detachment slide;
RTS, retrogressive thaw slump;
GTK, thermal erosion gullies

Question 20

true of false? Countries will rely on NETs to meet Paris agreemetn commitments

Answer 20

True

Question 21

Which chemical should be considered in global warming aside from CO2

Answer 21

CH4
N2o

Question 22

how is CH4 (methane) mainly produced?

Answer 22

naturally

Question 23

true or false? Clean energy tech, such as hydroelectricity, also have negative consequences on ecosystems and the planet

Answer 23

true