Flashcards · IB Diploma Programme Environmental Systems and Societies · Topic 4

Water flashcards

20 cards on Topic 4, subtopics 4.1 to 4.4. Pick a subtopic or study them all.

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What drives the hydrological cycle?: Solar energy and gravity. It is the system of storages and flows that moves water between the oceans, atmosphere, land and living things.
Water transfers versus transformations: Transfer: water moves without a change of state (infiltration, runoff, advection, precipitation). Transformation: the state changes (evaporation, condensation, melting). A change of state is the test.
How do you calculate residence time?: Residence time = storage ÷ flow rate. Example: an aquifer holding 150 km³ recharged at 0.5 km³ per year → 300 years. Pumping faster than recharge mines it like a non-renewable resource.
How does urbanisation change the water cycle?: Impermeable surfaces mean less infiltration and more surface runoff, so lag time shortens and flood peaks are higher.
Thermohaline circulation and upwelling: Thermohaline circulation: deep ocean circulation driven by differences in temperature and salinity. Upwelling: the rising of cold, nutrient-rich deep water to the surface, supporting high productivity.

What is water security?: Reliable access to enough safe water for people and ecosystems, with an acceptable risk from floods and droughts.
Physical versus economic water scarcity: Physical: there is not enough water in the region. Economic: water exists but people cannot afford or reach it.
What are the water-availability thresholds per person per year?: 1,700 m³ or more: no stress. 1,000–1,699 m³: stress. 500–999 m³: scarcity. Below 500 m³: absolute scarcity. Remember 1 km³ = 10⁹ m³ when dividing by population.
Water footprint versus virtual water: Water footprint: the total freshwater used to produce what a person or country consumes. Virtual water: the water embedded in traded goods.
How do you evaluate a water-security strategy?: Say whether it increases supply or reduces demand; give one benefit and who gains; give one environmental and one social or economic cost; judge under what conditions it would work best.

What are MSY and CPUE?: Maximum sustainable yield (MSY): the largest catch that can be taken every year without shrinking the stock. Catch per unit effort (CPUE): catch ÷ fishing effort, a proxy for stock size.
Why can a steady catch hide a collapsing fish stock?: If effort rises, the total catch can hold steady while CPUE falls. Falling CPUE with rising effort means a shrinking stock.
Name four fishery controls and one limit of each: Quota: needs honest reporting; discards may rise. Mesh size: does not cut overall effort. Closed season: effort may shift to other months. No-take marine protected area: needs patrols; fishers lose grounds.
What is the feed conversion ratio in aquaculture?: Feed mass ÷ increase in body mass (no units). A lower value means the farmed organism turns feed into body mass more efficiently. Aquaculture is not automatically sustainable: name its impacts.

Point versus non-point source pollution: Point: from one identifiable outlet, such as a pipe, which can be licensed and monitored. Non-point: from many diffuse sources, such as farm runoff, which is much harder to control.
What is biochemical oxygen demand (BOD)?: The oxygen used by microorganisms to break down organic matter in a water sample over a set time. BOD is the demand; dissolved oxygen is the supply left. High BOD usually goes with low dissolved oxygen.
Outline the stages of eutrophication: Nutrients (nitrate, phosphate) enter → algal bloom → light blocked, plants die → decomposers use oxygen → animals die → more nutrients released → positive feedback. Decomposers, not algae, cause the fall in oxygen.
What is an indicator species?: An organism whose presence or absence shows the level of pollution. It gives an indirect measurement: a record of conditions over time, unlike a chemical snapshot.
Bioaccumulation versus biomagnification: Bioaccumulation: build-up of a persistent pollutant within one organism. Biomagnification: rising concentration at each higher trophic level. Factor = higher-level concentration ÷ lower-level concentration (0.2 → 5.0 ppm gives 25).
What are the three levels of pollution management?: Change the human activity that produces the pollutant; control its release; clean up and restore the damaged ecosystem.