The Physical Environment (AS); The Hydrosphere (Complete)

Question 1

What is the hydrosphere?

Answer 1

Total amount of water on the planet

Question 2

Why is water a significant resource?

Answer 2

It is renewable & essential for all living organisms. Human Society has only been able to develop easily where water is available

Question 3

What are the most prominent human uses of water? (Use %)

Answer 3

Agriculture - 70%, eg. Irrigation
Industry- 20% eg. Cooling, heating, washing, solvent
Domestic uses- 8% eg. Flushing toilets, washing clothes/dishes, hygiene

Question 4

What are the list of reasons for an increasing demand for water?

Answer 4

• Increase in population
• increase in per-capita use w/ increased affluence
  In the poorest communities, there is no piped supply and so water is often limited to the amount that can be carried. As piped water becomes mare available & people more affluent, modern appliances are more common.
• increased irrigation of farmland
  As commercial agriculture expands, increased income allows ↑ irrigation schemes, the water of which may be pumped from aquifers/rivers. Irrigation now uses more water then all human uses combined.
• industrialisation
  Industries have varying water requirements. Heavy industry like chemical & steel use much more water than lighter manufacturing industries

Question 5

What are the reservoirs of water?

Answer 5

Oceans- 97%, residence up to 4000 years
Land ice- 2%, residence 20-100 years
Groundwater- 0.7%, 100-10,000 years
Lakes,rivers- 0.01%, 2 months-100 years
Soil moisture- 0.005%, 2 months
Atmosphere- 0.001%, 10 days
Living organisms- 0.00004%, 1 week

Question 6

Why can the importance of water not be predicted from its quantity?

Answer 6

Some reservoirs are abundant but are transferred slowly, like groundwater
Others have a small total quantity but are transferred quickly, like atmospheric water

Question 7

How can you calculate residence time?

Answer 7

Volume of water in reservoir/mean transfer time

Question 8

Why do human activities impact the hydrological cycle and how does this vary?

Answer 8

-Affect the transfer rates in the cycle, upsetting exiting dynamic equilibria
-This changes amount of water in different reservoirs on global/regional/local scales
-The rate of change can vary, eg- some glaciers are shrinking rapidly while others are slowly changing
-The extent and direction of the changes may differ in different areas, eg- one area declining rainfall another increases

Question 9

What is the main impact of the industrial/domestic use of water?

Answer 9

-On water quality, through the release of pollutants
-Their impact on the hydrological cycle tends to be local & most obvious where large urban centres have developed in areas w/ restricted water supply

Question 10

How does deforestation impact the hydrological cycle?

Answer 10

-Vegetation intercepts rainfall which may evaporate before reaching ground
-Trees also return a lot of water from soil to atmosphere by transpiration
-The loss of trees can cause a significant reduction in precipitation in downwind areas as more water infiltrates ground/runs off into rivers

Question 11

How does agriculture impact the hydrological cycle?

Answer 11

-Soil can be compacted by use of heavy farm machinery/livestock trampling
-Water doesn’t infiltrate easily into compacted soil so soil moisture levels drop, runoff increase
-Crop irrigation increase evaporation rates
-Loss off soil biota like worms reduces infiltration, increases surface runoff & reduce water retention by soil

Question 12

How dies urban development impact the hydrological cycle?

Answer 12

-Urban areas often have impermeable surfaces like concrete,tarmac
-This reduces infiltration while increasing rate of runoff
-Rapid runoff from large urban areas can increase river flooding downstream

Question 13

How does global climate change affect the hydrological cycle?

Answer 13

-Higher global temperatures affect rates of melting, evaporation, condensation & wind patterns
^These combined with to alter the type, amount, timing & location of precipitation
-More rapid melting of snow & ice—> caused by warming associated w/ global climate change
-Snow fall in cold weather & later melting in warm weather reduces extremes in river flow, so loss of ice may increase flooding after heavy rain & low river flow during periods of low rainfall

Question 14

How is river water abstraction impactful and not impactful depending on the situation?

Answer 14

-Some river water abstraction= little impact on river as used water is cleaned, returned to river
-But, rivers have often been used to carry away wastes
-Some abstractive uses do not return water to river—> reduces downstream flow, eg agricultural irrigation

Question 15

How do reservoirs create habitat change and wildlife barriers?

Answer 15

Habitat change- flooding reservoir destroys previous habitats but also creates new, valuable ones. Wetlands= uncommon habitats in most regions, so reservoir may be more valuable than what was lost

Wildlife change- dam + reservoir act as barrier to wildlife that migrate along river, like salmon. Free movement along river= important part of recolonising areas that have become vacant in bad years, dam may prevent this

Question 16

How do reservoirs affect the river regime downstream of dams?

Answer 16

-Reservoirs may be used in 2 ways
-Water may be used to regulate river flow, holding water back in times of surplus to ensure adequate river flow in times of shortage—> reduces risk of flooding downstream + periods of lower flow, important for species like turtles who lay eggs in sandbanks
-Rapid flow period= important to wash away sediments from gravel river beds where salmon & trouts lay eggs
-Changes in river fluctuations can change river erosion & sedimentation, so also development of meanders

Question 17

How do reservoirs impact sedimentation?

Answer 17

-Sediments carried into reservoir will settle there + not be carried further downstream
-In past, they may have been important to fertilise floodplain downstream
-May also have built up river banks & coastlines & counteracted erosion

Question 18

How do reservoirs affect microclimates?

Answer 18

-Large body of water may change local climate
-High heat capacity of water helps reduce temp fluctuations—> warmer in winter, cooler in summer
-Water provides less friction than land—> windspeeds higher
-Greater evaporation from reservoir surface may increase humidity, cloud cover & precipitation downwind of reservoir

Question 19

What are the implications of the over-exploited rivers flowing into the Aral Sea?

Answer 19

-Syr Darya + Amu Darya rivers flow through Central Asia to Aral Sea (formerly 4th largest lake)
-Since 1960s, huge irrigation schemes in part of Soviet Union (now part of Kazakhstan) used river water to irrigate cotton & rice crops
-River flow—> Aral Sea declined, sometimes to 0. Area of lake reduced by 90% & pollution by pesticides, fertilisers, and industrial waste caused serious problems.
-Still disagreements betw. countries sharing river (Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, Krygystan)
-Abstraction for irrigation reduces downstream flow. Flow through HEP dams in summer may be reduced to store water for winter gen but this reduces availability of summer irrigation water downstream

Question 20

How is the River Nile over-exploited and why does this cause conflict?

Answer 20

-Longest river in world; flows through 10 countries incl Egypt, Sudan and Ethiopia.
-Long disagreement w/ countries over direct water abstraction for irrigation & construction of dams to regulate flow, give water, and generate electricity
-As populations grow + these countries develop economically, demand for water may increase and risk of conflict may grow.

Question 21

What are the implications of the Rivers of Tibet being over-exploited?

Answer 21

-Tibet= formally independent, now part of China since 1950
-Tibetan plateau—> source of many of Asia’s major rivers, w/ more than 1500m people depending on water from the rivers Indus, Ganges, Yellow rivers, Mekong and more.
-Growing populations + increased demand for agriculture, industry may lead to water shortages & conflict between countries
-Issue of water shortages may be made worse by seasonal fluctuations in river flow due to climate change
-Melting of glaciers in Himalayas maintain river flow in dry seasons but receding glaciers may produce less reliable river flow in future

Question 22

What are some other examples of over-exploited rivers and their locations?

Answer 22

Colorado; USA, Mexico
Murray-Darling; Australia
Yellow River; China
Indus; Pakistan
Euphrates & Tigris; Turkey, Iraq, Syria
Jordan; Isreal, Lebanon, Jordan,Palestine

Question 23

What does the abstraction of rivers reduce and what does this affect?

Answer 23

-Often reduces downstream flow
-Affects river and lake it feeds, some rivers completely cease to flow

Question 24

What are aquifers and why do they need certain features?

Answer 24

-Bodies of rock, holds water which is exploited as a resource
-For a rock to form an aquifer must have certain features

Question 25

What features are necessary for aquifers?

Answer 25

-Porosity; measure of proportion of rock’s volume that is space, therefore can hold water. Chalk, limestone and sandstone= porous rocks that can form aquifers

-Permeability; measure of ease with which fluids may flow through rock bc of interconnections betw spaces & their size. Materials like clay are porous but pores= too small for water to flow through easily

-Associated geological structure; rock below water-bearing rock must be impermeable to prevent escape of water. Granite & clay= suitable impermeable rocks. Some above rock must be permeable; allows recharge of aquifer

Question 26

How does abstraction of water by humans affect aquifers and why?

Answer 26

-Natural # of water in aquifer= state of dynamic equilibrium of natural inflow/recharge of water into aquifer & water flowing out of aquifer.
-If abstraction of water by humans > rate of recharge= volume of water in aquifer will decline. May be long time before this as original volume stored may have been v large.
-Reduction of water in aquifer may have serious consequences

Question 27

What are the consequences of aquifers not being recharged for a long time?

Answer 27

-Some aquifers= recharged during last ice age 10-20,000 years ago (global climate was wetter)
-Many of these aren’t currently being recharged—> exploitation will eventually lead to shortages
-Some contain huge volume of water + will last long time, but relying on this long-term is dangerous as supplies aren’t sustainable

Question 28

What is the property of ancient aquifer water and what can this cause?

Answer 28

-Ancient aquifer water= often saline, can cause soil salinization as irrigation water evaporates, leaving salt behind
-Can cause osmotic dehydration + death of crops

Question 29

How do over-exploited aquifers cause changes in surface hydrology?

Answer 29

• Many rivers, lakes & marshes → fed by groundwater flowing out of aquifers
• If groundwater = overexploited, water table may be ↓, reducing/ stopping outflow of water into water → dries up

Question 30

How do over-exploited aquifers result in ecological impacts?

Answer 30

-If water table → lowered then plants w/ higher water requirement will die/ become less abundant as fail to compete w/ plants that have a ↓ requirement for water.
-Aquatic/ semi-aquatic animals will die if wetlands dry out
Other species may be affected, even though they don’t rely on water, as they depended for food on species that needed the water

Question 31

How do over-exploited aquifers result in salt water incursion?

Answer 31

-Coastal areas → water table may be slightly ↑ than sea level
-As rainwater percolates down to aquifer, water flows sideways & out into sea
-This seawards flow of freshwater prevents seawater from flowing → aquifer under land surface
-If aquifer = overexploited, sea water from sea/in rock under sea flows sideways → aquifer to replace freshwater
-Salt makes aquifer water unsuitable for irrigation → could kill crops by osmotic dehydration

Question 32

How do over-exploited aquifers result in subsidence?

Answer 32

-Water no longer present in interstitial spaces in rock cannot provide support for rock particles so will be compacted by weight of material above
-Will cause subsidence at surface → can cause serious damage to buildings & pipelines

Question 33

How do over-exploited aquifers result in reduced supplies?

Answer 33

• If extraction rate > recharge rate → volume of water available for abstraction =↓
• unsustainable use of aquifer water may have carried on for many years before problems became obvious → human activities relying on it may suddenly have to stop
• nearly 1/ 2 world’s pop live in countries over-exploiting aquifers

Question 34

How can aquifer depletion be monitored?

Answer 34

-Aquifer water levels can be monitored by checking level of water table in wells / boreholes → this is very slow & difficult to coordinate on large scale
- NASA operates 2 GRACE (gravity recovery & climate experiment)
-Orbit → affected by force of gravity, influenced by mass of water in aquifers below flight path
-Entire Earth = surveyed every 30 days

Question 35

How is the High Plains Aquifer an example of an over-exploited aquifer?

Answer 35

• Includes Ogollala Aquifer - extends <450,000 km² in mid-west states
• one of most important agricultural regions of the world & food production relies on irrigation w/ aquifer water → largely paleowater (fossil water) recharged aquifer during/ before last ice age
• long-term abstraction rates for agriculture >current recharge rates

Question 36

How is the North China Plain an example of an over-exploited aquifer?

Answer 36

• Largest agricultural region in China w/ fertile soil but few rivers → groundwater used for irrigation
• growing demand for irrigation water & demands of growing pop caused water table of aquifer to ↓ by approx 1m per year

Question 37

What measures are being introduced to reduce water use at the North China Plain?

Answer 37

• Low-pressure irrigation pipes used to ↓ leaks;
• most important crops = wheat & maize but growth of crops requiring less water proposed;
• consumers charged for volume of water used to encourage conservation
• large scale afforestation projects developed to sequester carbon as method of tackling climate change &↓ soil erosion but transpiration by trees ↓ soil moisture levels
• plans to transfer water 450 km from Yangtze River → area

Question 38

How are aquifers in Malta examples of over-exploited aquifers?

Answer 38

Malta has precipitation rate of 550mm but evapotranspiration rate = 400 mm, so only 150mm available for use
Many of island’s aquifers → contaminated by industrial/ agricultural wastes or over-exploited so water table ↓, salt water incursions contaminated freshwater
- sewage effluent used for agricultural irrigation
- large proportion of public water supply now provided by desalination of seawater → very expensive

Question 39

Why may it be necessary to exploit previously unused resources/increase exploitation rate of existing supplies?

Answer 39

To satisfy the growing population & increased per-capita demand

Question 40

Why is rainwater collection important?

Answer 40

-Increasingly important in areas where public supplies can’t match consumer demand eg many cities in India
-↓ urban flooding after heavy rain
-Important in rural areas where there’s no public water supply → water often cleaner than other sources like rivers

Question 41

Why are rivers important sources of water?

Answer 41

-River water = often most convenient source of water
-Being long → accessible over large land area
-Natural contaminants rarely serious problem, human problems not usually problem until population density ↑ to point where waste from community upstream didn’t break down before reaching next community

Question 42

What are the main features affecting the usefulness of a river?

Answer 42

• Total annual water flow (river discharge);
• flow fluctuations;
• level of natural contaminants;
• pollutants from human activities

Question 43

What do reservoirs allow?

Answer 43

The storage of water from times when there’s a surplus of water, so can be used when there’s a shortage

Question 44

How does topography influence reservoir site selection?

Answer 44

-Main cost of reservoir construction = building dam
-Income created by reservoir = from # of water it can provide
-Ideal topography → narrow exit from larger deep basin so relatively small dam = hold back huge volume of water

Question 45

How does geology influence reservoir site selection?

Answer 45

• Rock beneath must be impermeable so water can’t percolate into rock, be lost
• rock should also be strong enough to support weight of dam & reservoir w/out faults/ seismic activity that could cause an earthquake, collapse dam

Question 46

How does catchment area influence reservoir site selection?

Answer 46

-This → area of land over which rain will flow/through ground then → river
-So ability of reservoir to provide water = controlled by reservoir site itself & area collecting for it
-Even if it hasn’t rained recently, may be a lot of water from previous rain on its way to reservoir
-Catchment area doesn’t have to be around reservoir itself, may be in mountain range w/ water flowing → river carrying water to reservoir site downstream.

Question 47

How does water supply influence reservoir site selection?

Answer 47

-Ideally → rainfall / river inflow = regular + large volume
-Climate not too hot/dry to cause excessive evaporation losses

Question 48

How does pollution risk influence reservoir site selection?

Answer 48

-Land uses in catchment area shouldn’t pose serious pollution risk to water
-Main risk caused by toxic pollutants from industry & agricultural pesticides
-Pollutants like sewage & manure = biodegradable, break down relatively quickly. Unlikely to become as concentrated as could in a river
-If flooded area of reservoir → covered w/ forest/lots of dead vegetation carried into water → may decay anaerobically, releases methane adding to global climate change

Question 49

How does sedimentation influence reservoir site selection?

Answer 49

-Soil erosion in catchment area can make inflow river very turbid → sedimentation in reservoir.
-Gradually ↓ volume of water reservoir can hold

Question 50

How does infrastructure influence reservoir site selection?

Answer 50

-Building dam, treating water & transporting it → area of demand requires = workers, building materials, access routes & machinery
-Convenient site near are a of demand may be chosen rather than site supplying more water but is isolated/difficult to reach

Question 51

How does existing land use & its conflicts influence reservoir site selection?

Answer 51

-Use of land that’s to be flooded can’t be so important that it can’t be lost
-Loss: benefit analysis must be considered → balance benefits of having reservoir against what’s lost
-In UK = large urban areas & important wildlife conservation areas → probably protected, while agricultural land = less valued
-Other countries may assess priorities differently

Question 52

What are estuary barrages and their advantages/disadvantages?

Answer 52

-Freshwater reservoir created by building a dam across an estuary where river enters sea
-Had fewer land conflicts than those on land (has to be flooded)
-Change important inter-tidal habitats, create obstacle for shipping & can be polluted by human activities anywhere in rivers catchment area

Question 53

Why is desalination of water uncommon?

Answer 53

Very energy-intensive & expensive; only used in countries where seawater is available + adequate supplies of freshwater

Question 54

How can aquifers be artificially recharged and why is this needed?

Answer 54

-Aquifer water can be abstracted during dry seasons but recharge rate may be low in wet seasons when infiltration capacity of surface rocks is exceeded & surplus runoff flows—> sea via rivers
-Aquifer supplies can be maintained using surplus water in periods of high rainfall to recharge aquifers by pumping it underground/diverting it—> lagoons, can infiltrate into ground gradually

Question 55

How can reservoirs regulate river flow?

Answer 55

-Human activities often increase extremes in river flow, eg deforestation/urbanisation within river catchment area
-Reservoirs can be used to regulate the extremes
-Times of low rainfall—> reservoir maintains river levels by opening dam to allow more water into river
-Times of heavy rain—> reservoir stores surplus water to reduce flooding downstream

Question 56

How and why are inter-basin transfers used + what countries use this?

Answer 56

Canal + pipe systems can be used to transfer water from areas w/ surplus—> deficit
Used in countries like; China, Russia, Australia, Wales, England

Question 57

Why are unexploited aquifers important?

Answer 57

Newly discovered aquifers, like in N Africa & Kenya, may increase water supplies

Question 58

How does afforestation benefit rivers?

Answer 58

-Trees—> reduce soil erosion & reduce rate of rainwater flow into rivers
-Reduces fluctuations in river level—> helps reduce flooding post heavy rains + maintain river levels in low rainfall

Question 59

What are methods of low-volume uses of water to increase water conservation?

Answer 59

-Low water appliances; eg washing machines, dishwashers, tap timers, dual flush toilets

-Xeriscaping; management of gardens, parks & urban spaces, eg roundabouts by planting them w/ species adapted to dry conditions so demand less water

-Low-volume irrigation; drip irrigation delivers water directly to plants—> lower evaporation losses than overhead sprays

Question 60

What are the methods of recycling used water to increase water conservation?

Answer 60

‘Grey water’= retaining water that’s been used but is still quite clean. It’s then reused for other purposes, eg water for showers can be used to flush toilets/garden uses

Question 61

What are the consequences of contaminated water and what methods can be used to treat it?

Answer 61

Activities may produce contaminated water; cant be reused + may pollute other sources like rivers
Effluent treatments processes can treat contaminated water, eg:
-Oil pollution control
-Sewage treatment
-Acid mine drainage
-control of heavy metal waste
-landfill leachate treatment
-buffer strips next to rivers; reduces fertiliser runoff

Question 62

How is water commonly wasted and what can be done to combat this?

Answer 62

-Lots of water infrastructure in UK= old, poor condition
-Approx 20% water intended for public use—> lost from leaking pipes and dripping taps

-Repairs + good maintenance can fix this
-Water meters that match charges consumers pay to vol of water used—> encourage water conservation

Question 63

Why is water treatment needed?

Answer 63

-Some abstracted water may not be suitable for use
-Quality problem may be natural/man-made

Question 64

What are examples of water uses and their quality requirements + problems if not met?

Answer 64

Potable water for public supply- No pathogenic microorganisms, toxins at acceptable level, looks/smells/tastes good. If not met; public health risks and complaints

Spray irrigation- Low turbidity, low # of absorbable toxins for crops, like metals. If not met; blockage of water pipes, contamination of food

Textile washing w/ soap- ‘soft’ water w/ low calcium conc. If not met; scrum forms on textile

Power station condenser cooling water- No gross solids. If not met; Pipe blockage

Industrial boiler water- no dissolved minerals. If not met; mineral deposits build up, fall in heat exchange, pipe blockage

Question 65

What is sedimentation in the water treatment process?

Answer 65

Water allowed to remain static—> lets suspended solids like silt to settle

Question 66

Why are screens important in the water treatment process?

Answer 66

-Many items enter fluid flow—> problems later on
-Metal grills/meshes used to remove vegetation & litter like plastic/paper

Question 67

-What is aeration and why is it important in the water treatment process?

Answer 67

-Bubbles of air/water sprays used to aerate water, ensure high dissolved oxygen content
-Anaerobic water sources may have hydrogen sulfide from decay of organic matter; makes water smell of bad eggs
-Some dissolved metals= toxic, give water bad taste—> removed by aeration as become insoluble

Question 68

What is flocculations/coagulation and clarification, how is it important in the water treatment process?

Answer 68

-Clay particles—> don’t settle out in sedimentation lagoons bc electrostatic charges on surface cause them to repel each other
-Can be neutralised by adding flocculants, eg aluminium sulfate/polyelectrolytes. Mixed quickly w/ water—> passed into clarifier tank where particles can settle

Question 69

What does filtration involve in water treatment processes?

Answer 69

-Some treatment plants= filters—> used to remove any remaining bacteria & suspended solids.
-Often involve slow flow through layers of sand + gravel

Question 70

How are activated carbon filters used in the water treatment process?

Answer 70

Particles of activated carbon—> used to remove organic chemicals, eg pesticides; absorb into carbon particles

Question 71

How is sterilisation done in the water treatment process?

Answer 71

-Addition of chlorine, ozone or exposure to UV light—> used to sterilise water + kill pathogens
-Chlorine= most common process but if water is from peaty sources, organic matter may be present—> could react w/ chlorine, make toxic substances. Here, ozone is added/UV light used.
-Addition of chlorine should keep water sterile during distribution but is gradually lost. Chloramine keeps water sterile for longer (breaks down gradually, releases chlorine)

Question 72

Why is pH control needed after sterilisation in the water treatment process, and how is this done?

Answer 72

-Sterilisation w/ chlorine can make water too acidic
-pH adjusted by adding crushed lime

Question 73

What does fluoridation involve and why is it done in the water treatment process?

Answer 73

Fluorides added to water in some areas to improve dental health of people drinking the water

Question 74

What does ion exchange involve in the water treatment process and why is it used?

Answer 74

-Toxic ions, eg lead/mercury/arsenic can be removed from water w/ ion exchange resins.
-The toxin ions absorb onto polymer beads/particles of zeolite
-Ion exchange—> also used to remove calcium ions & magnesium ions to make ‘soft’ water

Question 75

What is the process of reverse osmosis and why is this used in the water treatment process?

Answer 75

-Seawater—> most abundant source of water but high salt content= unusable, except for uses where its composition is unimportant, eg condenser cooling water for power stations
-Removing salt from seawater via desalination= expensive, only carried out if other sources of water are unavailable
-Saline water—> filtered at very high pressure through partially permeable membranes of v small polyamide tubes. Lots of energy needed for the high pressure= very expensive
-Fresh water collected—> approx 1/2 OG volume. Remaining v salty water= returned to sea

Question 76

What is distillation in the water treatment process?

Answer 76

Water- boiled by heating and/or reducing pressure. Steam produced- condensed & collected