elss sg5

Question 1

what are negative and positive feedback loops and dynamic equilibrium?

Answer 1

negative feedback: self-limiting, lessens the effect of the original change e.g. CO2 in atmosphre increases = extra CO2 causes more plant growth = plants remove and store CO2= atmospheric store reduces.
positive feedback: self-enhancing, causes further change or a snowball effect e.g. temps rise = evaporation increases = amount of water vapour in atmosphere increases = greenhouse effect increases and repeat.
dynamic equilibrium: despite inputs and outputs in a system changing in the short term, in the long term balance will be maintained

Question 2

effect of urbanisation, farming and forestry on cycles

Answer 2

WATER:
urbanisation: woodland replaced by concrete/tarmac, impermeable = less infiltration = overland flow = more flooding.
farming: vegetation and biomass removed for farming, less interception mroe ifniltration = more overland flow.
forestry: planting of coniferous trees = more interception and interception loss via evapotranspiration = reduced run off and river discharge.
CARBON:
urbanisation: vegetation removed for urban areas, reduces store = less photosynthesis, urban areas emit roe carbon emission e.g.vehicles.
farming: If trees cleared for crops = reduced photosynthesis = reduced above ground store
forestry: increased photosynthesis = increased above ground store

Question 3

impact of surface water extraction: aral sea

Answer 3

• on boundary of kazakhstan, uzekistan in central asia and used to be supplie yb the amu durya and syr darya rivers. From 1930s, water extraction has occured for crop irrigation - mainly silk and cotton crops.
• sea level has dropped 10m, surface area shrunk from 70,000km2 to 25,000km2.
• impact on flows and stores: summers are warmer, winters cooled. HUmditiy fallen by 28%, mroe evaporation with the warm conditions, less precipitaion, creates dust storms due to dryness.
• created a PFL: Less surface water = less evaporation = less water vapour = less condensation = less
  precipitation = continues to get drier.

Question 4

impact of water extraction on groundwater

Answer 4

• The London basin is aan artisan basin at the centre of a synclinee (dipping rocks that form a bowl structure), groundwater is held by a band of chalk.
• Industrial revolution: groundater exracted for industry, its store decreased due to overexploitation, levels fell by 90 metres - water table fell. But there is an increase in percolation and infiltration so more water can be stored.

Question 5

impact of fossil fuels on carbon cycle

Answer 5

• humans have produced 1997GT of carbon since 1750 - 68% of these come form fossil fuels. 44% is stored in the atmosphere, 29% stored in the oceans and 26% on land.
• CCS - carbon capture and storage: Capturing carbon emissions from factories, transporting it and storing it in underground in geologically suitable locations. UK is investing in this in North sea, it could capture 1,000,000 tonnes of co2 a year. BUt it is expensive to install, questions over safety e.g. possible CO2 leakages?

Question 6

diurnal and seasonal changes in cycles

Answer 6

Alaska has more seasonal changes: temp range of 33 degrees and large changes in daylight hours creates distinct seasons. In the Amazon the temp range is less than 2 degrees and daylight hours are the same all year.
Amazon has more diurnal changes: 12 hrs of sunlight & 12 hrs of daylight means evapotranspiration and
photosynthesis are both much higher in the daytime. In Alaska it can be 24hrs of day (in summer) or night (in winter) for 8 months of the year.

Question 7

long terms changes in the cycles

Answer 7

• 10% of our land today 30% during the last glacial was covered in ice. I the last glacial, sea level heights were 100 – 130m lower.
• concentration of CO2 in atmosphere today is 418ppm , it was 180ppm 20,000 years a go.
• during last glacial: increase in store of carbon in cryosphere - plants and soil trapped in ice, decrease in store in biomass. In an interglacial: less in cryosphere adn mroe in biomass.
• last glacial: icnrease in water store in cryosphere - it covered more land mass, less water stored in biomass,soils and oceans. in an interglacial: decrease store of water in cryosphere, increase store of water in oceans and atmosphere.