People and the water cycle (not in specified)

Question 1

name 3 land use changes affecting carbon and water cycle

Answer 1

Urbanisation
Farming
Forestry

Question 2

what is urbanisation and how does it affect the two cycles?

Answer 2

the conversion of land use from rural to urban, farmland and woodland replaced for housing, offices etc. natural surfaces give way to concrete, brick or tarmac.
these surfaces are largely impermeable + allow little infiltration. = high proportion of water from precipitation quickly flows in streams, leading to rapid rise in water level.
also encroaches on floodplains, which reduces water storage capacity in drainage basin, increasing river flow + flood risks.

Question 3

what is farming and how does it affect the two cycles?

Answer 3

brings changes to vegetation + soils.

• clearance of forest for farming reduces carbon storage in above + below ground biomass. also reduced by ploughing + exposure of soil organic matter to oxidation. further losses through harvesting of crops with only small amounts of organic matter returned to soils. soil erosion is common and is most severe when crops have been lifted + soil have little protective cover.
• changes to carbon cycle = less apparent on pasture land. carbon exchanges through photosynthesis are generally lower than in natural ecosystems. due to lack of biodiversity + the growth cycle of crops compressed into 4/5 months.
• interception of rainfall by annual crops is < the forest + grassland, so is evaporation + transpiration from leaf surfaces. ploughing increases evaporation + soil moisture loss + furrows ploughed downslope act as drainage channels, accelerating run off + soil erosion. Infiltration is greater, artificial drainage increases the rate of water transfer to streams. surface run - off increases where heavy machinery compacts soils. peak flows on streams draining farmland are higher than in natural ecosystem.

Question 4

how does forestry affect the water cycle?

Answer 4

water cycle changes:

• higher rates of rainfall interception in plantations in natural forests.
• increased evaporation, large proportion of intercepted rainfall is stored on leaf surfaces + is evaporated directly to the atmosphere
• reduced run off + stream discharge, high interception + evaporation rates + absorption of water by tree roots, drainage basin hydrology is altered. Long lag times, low peak flows + low total discharge.
• transpiration rates increased (compared to farmland + moorland)
• clear felling creates sudden but temp changes to local water cycle, increasing run off, reducing evapotranspiration + increasing stream discharge.

Question 5

how does forestry affect the carbon cycle?

Answer 5

• increases carbon stores, soil is even larger carbon oil. (in UK forest soil = 500 tonnes C/ha
• forest trees extract CO2 from the atmosphere + sequester for 100s years. however only become an active carbon sink for the first 100 years after planting thus amount of carbon captured levels off + is balanced by inputs of little to soil, the release of CO2 In respiration + activities of soil decomposers. usually after this time trees are felled + reforestation happens.

Question 6

what is water extraction and do humans affect it?

Answer 6

water is extracted from surface + groundwater to meet public, industrial + agricultural demand.
direct human intervention in the water cycle changes the dynamics of river flow + groundwater storage.

Question 7

water extraction on river Kennet facts

Answer 7

• drains an area of 1200km2
• upper catchment mainly comprises on chalk which is highly permeable
• its water filtered through chalk, exceptional clarity, high oxygen levels + is fast flowing
• Kennet supplies water for local industries, agriculture + public use

Question 8

how does Kennet extraction + its catchment have an impact on regional water cycle?

Answer 8

• rates of groundwater action have exceeded rates of recharge, + falling water table has reduced flows in river by 10-14%
• during the 2003 drought flows fell by 20% + in dry conditions of early 1990s by up to 40%
• lower flows have reduced flooding + temp areas of standing water + wetlands on the Kennet’s floodplain

Question 9

what is an aquifer?

Answer 9

permeable or porous water bearing rocks eg chalk

Question 10

what is an artesian basin?

Answer 10

when sedimentary rocks from a basin like structure, an aquifer confined between impermeable rock layers may contain groundwater which is under artesian pressure. if this is tapped by a well, the water will flow to the surface under its own pressure.