The Hydrosphere Flashcards
What are the 7 reservoirs of water in the water cycle?
Oceans
Land ice
Groundwater
Atmosphere
Living organisms
Lakes and rivers
Soil moisture
What is residence time (RT)?
The average amount of time that a water molecule is present in a reservoir of water
What is transfer rate?
The volume of water that is transferred over a period of time (e.g. litres per second)
What is the calculation for residence time?
RT = Volume of water in a reservoir / Mean transfer rate
What is the estimated volume of water in Earth’s hydrosphere?
1,500,000,000 km3
Which reservoir has the longest RT?
Groundwater (5000 years)
Which reservoir has the shortest RT?
Living organisms (7 days)
Which reservoir contains the largest volume of water?
Oceans (97% of water on Earth)
Which reservoir contains the smallest volume of water?
Living organisms (0.00004%)
Where does the energy that drives the water cycle come from?
The Sun
What is abstraction?
Taking water from a natural reservoir for human use
What are some examples of human activities which affect the water cycle?
Urbanisation, agriculture, deforestation, afforestation, global climate change
What are the effects of agriculture on the water cycle?
- Abstraction for irrigation can cause aquifer depletion (over-drafting)
- Heavy machinery or livestock trampling can cause soil compaction which would increase surface runoff
What is the link between interception and infiltration?
Water is more likely to infiltrate when slowed down by interception
What are the 4 factors which cause a change in the demand for water?
Change in population
Change in affluence
Change in industry
Change in agriculture
How does population affect demand for water?
Increased population leads to increased demand
How does affluence affect demand for water?
Increased affluence (wealth) leads to increased demand due to more money and appliances
How does industry affect demand for water?
Heavy industry (such as paper production) requires more water than the service industry
How does agriculture affect demand for water?
Intensive agriculture requires more water than small-scale or subsistence agriculture
What are the consequences of human impacts on the water cycle?
- Dynamic equilibria in the hydrological cycle are negatively affected as transfer rates are changed
- Reservoirs of water may become depleted and be unable to recover immediately
What is per capita water use?
The mean water use per person within a country (m3/yr)
What is GDP?
Gross Domestic Product is a measure of the monetary value of all goods and services produced within a country in a year (used as a measure of affluence)
What is a water footprint?
The volume of water needed for the production of goods and services consumed by a person or a group of people (e.g. business, country)
What are some abstractive uses of water?
Desalination, HEP, mining, transportation, heavy industry, domestic use
How has unsustainable exploitation affected the Mekong River?
Increasing water demand due to population rise and agricultural use has caused pressure on the fishing industry (largest inland fishing industry in the world) as well as water scarcity
What is a reservoir and why are they built?
An artificial lake in which water is stored (dams are built to control the volume of water leaving the reservoir)
What are the advantages of reservoirs?
- Water security during droughts
- Stores for irrigation
- HEP generation
- Improves sanitation in urban areas
What are the disadvantages of reservoirs?
- Large land requirement
- Human displacement and relocation
- Alters fish migration patterns
- Micro-climatic changes
How do reservoirs cause habitat change?
The area upstream of a reservoir is flooded and becomes a freshwater habitat, whereas the area downstream of a reservoir becomes a dry habitat
How do reservoirs create wildlife barriers?
The natural flow of a river is prevented which creates a migration barrier for marine organisms, especially fish which would normally travel upstream to spawning grounds
How do reservoirs cause changes in river flow?
Less water arriving downstream may cause the river to reduce in size (impact on water availability)
How do reservoirs cause sedimentation?
Suspended material settles and builds up behind the dam as regular river flow is prevented (reduced reservoir capacity and nutrient availability downstream)
How do reservoirs cause micro-climatic changes?
Water affects local abiotic factors as it has a high specific heat capacity and retains thermal energy for a long period of time (moderates temperature extremes)
What are the examples of micro-climatic changes caused by a reservoir?
- Warmer than surrounding areas in winter
- Cooler than surrounding areas in summer
Which factors affect reservoir location?
Topography, geology, catchment area, water supply, existing land use, pollution risk, sedimentation, infrastructure
What is the ideal topography for a reservoir?
A valley with steep sides and a river (or a natural depression in the ground)
What is the ideal geology for a reservoir?
Impermeable rock base to prevent reservoir drainage (e.g. granite, clay)
What is a river’s catchment area?
The area where all runoff will flow into a particular river
What is the ideal catchment area for a reservoir?
A larger catchment area will increase the volume of water which is transferred to the reservoir
What is the advantage of a large catchment area?
Water will still flow through runoff into the river and reservoir during dry periods with little precipitation
What is the ideal water supply for a reservoir?
High levels of precipitation
What is the ideal existing land use for a reservoir?
Not located on or near existing designations, urban areas and agricultural land
Why must pollution risk be taken into account when siting a reservoir?
Chemical runoff from agriculture may concentrate in the reservoir due to runoff from farmland
Why must sedimentation be taken into account when siting a reservoir?
The amount of soil erosion within the catchment area should be low in order to reduce sedimentation (increased vegetation reduces soil erosion)
What is the ideal infrastructure for a reservoir?
Existing roads which would reduce the cost of new access roads to the reservoir
What is an estuary barrage?
A dam built across the mouth of a river which prevents freshwater reaching the ocean
- Migration barrier
- Prevents maritime transport
- Affects inter-tidal zones which may be legally protected by a designation
What is an aquifer?
A body of permeable rock which stores and transmits groundwater
What are the 3 main features of aquifer formation?
- Porosity
- Permeability
- Suitable geological structures
Why is porosity required for aquifer formation?
It is a measure of the proportion of a rock’s volume that is empty space and could store water
Why is permeability required for aquifer formation?
It is a measure of the ease of water flow through a rock due to pathways between spaces which allow for the downward movement of water into the aquifer
What are the suitable geological structures required for aquifer formation?
- Impermeable rock beneath the aquifer to prevent drainage
- Syncline basin on which the aquifer sits (curved)
What are some examples of porous and permeable rocks?
Chalk, limestone, sandstone
What are some examples of impermeable rocks on which an aquifer could sit?
Clay, granite
What are the 2 types of aquifer?
- Confined aquifer - situated between two layers of impermeable rock
- Unconfined aquifer - exposed to the surface and can be directly recharged
What is an artesian well?
A well that transports groundwater to the surface using hydrostatic pressure (no pumping required)
What is the water table?
The upper limit of groundwater within Earth’s surface (the boundary between the saturated zone and the unsaturated zone)
What are the 5 main consequences of aquifer overuse?
- Reduced groundwater supplies
- Subsidence
- Changes in surface hydrology
- Ecological impacts
- Saltwater incursion
What are the impacts of reduced groundwater supplies?
- Limited supplies for agriculture, domestic and industrial use
- Reduced food production and security
- Negative economic impacts (decreased GDP)
What is subsidence?
The downward movement of sediment and rocks, caused by the loss of hydrostatic pressure in the aquifer which leads to pores becoming empty and compacting
What are changes in surface hydrology?
Disappearance of surface water features if the water table drops (loss of lakes, rivers, ponds, wetlands)
What are the ecological impacts of aquifer overuse?
- Loss of freshwater habitats due to changes in surface hydrology
- Extinction of endemic species
- Species migration
- Loss of inter-species relationships
What is saltwater incursion?
Aquifer overuse in coastal areas causes the rock to draw in water from stores of salt-water in the ocean as the water table drops below sea level
Why is saltwater incursion particularly damaging?
- Groundwater has the longest RT of any reservoir (5000 years) and therefore salt water incursion may cause long-term contamination
- Water is unsuitable for irrigation and could kill crops through osmotic dehydration
Which 2 methods are used for monitoring aquifer water levels?
- Boreholes - physically monitor the height of the water table and can be compared to previous years
- GRACE satellites - Gravity Recovery and Climate Experiment
How do GRACE satellites work?
They carry out gravity surveys
- Increased mass below the surface increases gravitational pull (and vice-versa)
- An increase in mass indicates an increase in volume of water in the aquifer
What is a cone of depression?
A depression in the water table caused by over-abstraction around an artesian well
Which is the most important aquifer in the UK?
The London Basin - a confined aquifer in SE England with a reservoir rock of chalk and a base rock of clay
What is aquifer recharge?
The natural replenishment of groundwater stores in aquifers (mainly due to precipitation)
What are 2 examples of over-exploited aquifers?
- North China Plain - large scale irrigation has led to over-exploitation, causing subsidence and loss of surface water features
- Malta - lack of freshwater resources has led to over-exploitation, causing saltwater incursion and threats to food security
What are 3 examples of exploitation of new sources of water?
- Rainwater collection
- Rivers
- Seawater
What are the advantages of rainwater collection?
- Reduces urban flooding
- Provides water to rural areas with no public water supply
What are the 4 main features which affect the usefulness of a river?
- Total annual river discharge
- Flow fluctuations
- Levels of natural contaminants
- Human activity pollutants
What is the disadvantage of seawater?
Desalination is very energy-intensive and expensive
What are the 6 ways in which water can be sustainably managed?
- Artificial recharge of aquifers
- River-regulation reservoirs
- Inter-basin transfers
- Unexploited aquifers
- Afforestation
- Water conservation
What is artificial aquifer recharge?
The use of surplus water during periods of high rainfall to replenish groundwater stores
What are river-regulation reservoirs?
Dams can be operated to either decrease or increase the flow of water in a river during periods of high or low levels of precipitation
What are inter-basin transfers?
Water can be transferred from regions of water surplus to regions in demand (e.g. Wales to England)
What effect does afforestation have on the water cycle?
- Reduces soil erosion
- Increases interception which decreases runoff into rivers (prevents flooding)
What are some examples of water conservation?
- Low-water appliances
- Drip irrigation
- Use of recycled ‘grey-water’
- Water meters
How is litter removed from contaminated water?
Water is passed through screens (metal grids) to remove large items such as plastics
How are suspended solids removed from contaminated water?
- Sedimentation (water is stored for a number of days in large tanks to allow suspended particles to settle and then be collected)
- Flocculation (chemicals are added to neutralise the charge of suspended solids that have not settled such as clay)
How are metals removed from contaminated water?
An ion exchange resin such as zeolite is added and metals such as lead, mercury and arsenic adsorb onto it
How are organic pollutants removed from contaminated water?
- Activated carbon filters (use of fine C particles which have been treated at a high temperature to remove pesticides through adsorption)
- Aeration (oxygen is bubbled through the water which encourages aerobic bacteria to breakdown organic matter)
How is salt removed from contaminated water?
Desalination:
- Reverse osmosis (water is forced through a semi-permeable membrane - energy intensive)
- Distillation (Water is heated to allow evaporation and water vapour is condensed and collected)
How are pathogens removed from contaminated water?
Sterilisation is used to remove pathogens which could cause disease (using either O3, Cl or UV)
