Water Cycle Pack J Flashcards
(19 cards)
What is an aquifer?
Permeable and porous water-bearing rocks, such as chalk and sandstone
What is an unconfined aquifer?
Where rock is directly open at the surface of the ground and groundwater is directly recharged (e.g. by rainfall or snowmelt)
What is a confined aquifer?
Where thick deposits overly the aquifer and confine it from the Earth’s surface or other rocks
What is an artesian aquifer?
A confined aquifer containing groundwater under positive pressure
What is happening to the aquifer in Mexico City?
- Population is >20 million
- City is subsiding
- Buildings collapsing and railways/roads damaged
- 80% of supply comes from groundwater
- Impermeable surfaces limits recharge
What happened to the aquifer in London?
- Water levels went down during the Industrial Revolution
- Enabled houses with basements to remain dry
- When industry moved out of London, the aquifer should have recharged but this would flood basements and underground railway tunnels
- Therefore, Thames Water removes water from the aquifer to prevent this
How are aquifers recharged?
Natural:
- Precipitation falls on land surface, infiltrates into soils and moves through pore spaces to water table
- Surface water runoff from rivers, streams, lakes and wetlands
Artificial:
- Injection of water through wells
- Reservoirs keep water stores on the surface help water to infiltrate
E.g. dams, terraces, contour bunds
What physical conditions lead to humans having to extract groundwater rather than surface water?
- Low precipitation levels
- High temperatures
- Arid regions
How does groundwater move?
- Enters by infiltrating into the soil surface during or after a precipitation event
- Water percolates through the soil to bedrock
- Sub-surface water moves horizontally due to gravity or laterally from wetter to drier areas
- Travels into surface water bodies, re-emerges at surface as a natural spring and is lost via evaporation
- Abstracted from reserves by humans through digging boreholes/wells
What is over-abstraction?
- Extracting groundwater more quickly than it can recharge
- Driven by population growth and agricultural and industrial growth
- Coupled with rising temperatures and falling precipitation so groundwater reserves are depleted
- Environmental, financial and social consequences
What are the impacts of over abstraction on abstraction yields?
- Water table drops below level of existing wells
- Dries up wells as the groundwater becomes inaccessible
- Wells will need to be deepened or new wells installed
- Pumping costs increase to bring water to the surface
- Higher infrastructure costs and declining yields may make it unachievable
What are the impacts of over abstraction on surface water?
- Reductions of groundwater mean less water is available to flow into surface water bodies
- Groundwater maintains base low
- Flows will reduce
- Some streams/river may being ephemeral or intermittent
What are the impacts of over abstraction on ecosystems?
- Rivers, soils and streams dry out
- Fish are left stranded and die
- Wetlands dry out due to lack of water seeping to the surface
- This leads to a reduction in vegetation abundance and biodiversity
- Habitat loss, which impacts wildlife
What are the impacts of over abstraction on carbon cycling?
- More susceptible to wildfires
- This further damages soils and vegetation
- Large amounts of gaseous carbon are released through combustion
- Increases atmospheric greenhouse gas concentrations
- Reductions in water tables leads to drying of wetlands which increases carbon emissions from respiration
- Pore spaces in soil are filled with air not water
- Increases aerobic respiration from organisms
What are the impacts of over abstraction on salinsation?
- Water travels from wetter to drier areas as less water into surface bodies
- Seawater ingresses into aquifers/groundwater stores in coastal regions (saltwater intrusion)
- Saline water isn’t suitable to drink
- Na, Mg and Ca accumulate in soils as water evaporates and these soluble salts precipitate at the surface
- Reduces fertility which harms ecosystem functioning and crop yields
What are the impacts of over abstraction on subsidence?
- Water in soils/bedrock provides support for the overlying ground surface, buildings and infrastructure
- Weight of overlying infrastructure causes soils/rocks to collapse and compact
- Causes land subsidence
- Damages properties and risks to human life
What are the impacts of over abstraction on cultural services?
- Degrades a range of cultural services
- Services include leisure services provided by natural water courses/sources and positive impacts from spending time in healthy natural spaces
What are the impacts of over abstraction on water insecurity?
- Communities suffer from the wider effects of water insecurity
- Particularly affects developing countries
- Decline in agriculture as less water is available for irrigation so food production declines
- Limited industrial capacity
- Increased risk of disease as only dirty drinking water is available
- Disruption to education as girls are required to collect safe water instead of attending school
How can groundwater reserves be protected?
- Groundwater usage requires a license in the UK with checks to ensure that abstraction will not cause environmental degradation
- Environmental regulations to control pollutants entering waterways will protect current water reserves
- Water distribution infrastructure (e.g. pipe networks) Need to be good quality to prevent avoidable leakages of water which lead to further abstraction to replace what has been lost
