Water scarcity and water quality
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Define water quality.
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All Flashcards in Topic 7.3
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7.3.112 cards
Define water quality.
How clean and usable fresh water is — its levels of **nutrients, oxygen, sediment, salts and chemicals**.
Define eutrophication.
Enrichment of water with **nutrients (nitrate, phosphate)**, causing algal blooms and oxygen loss.
What is an algal bloom?
A rapid surface growth of algae that **blocks light** and later **uses up oxygen** as it decays.
What is a dead zone?
Water so low in oxygen (**hypoxic**) that fish and other animals cannot survive.
Define salinisation.
A **build-up of salts** in soil and water, often from over-irrigation in dry areas.
Point vs diffuse source?
**Point source** = one identifiable outlet (a pipe); **diffuse (non-point)** = spread across an area (run-off from fields).
Trace the eutrophication chain.
Nutrients to **algal bloom** to algae decay to bacteria use the **oxygen** to **dead zone** to fish die.
One human cause of eutrophication?
Fertiliser run-off (also sewage, detergents, industrial discharge) adding nutrients to the water.
One physical cause of eutrophication?
Shallow, warm, slow-moving or enclosed water that concentrates nutrients and speeds algal growth.
How does irrigation cause salinisation?
It raises the water table; as that water evaporates it leaves **salt concentrated at the surface**, poisoning crops.
Two ways agriculture pressures wetlands?
Fertiliser run-off causing eutrophication, and **draining/abstraction** altering the water flow.
What does a top [10] Examine answer need?
Two+ developed effects/stakeholders, an example, a weighing of relative severity, and a clear judgement.
7.3.212 cards
Define water scarcity.
When there is **not enough fresh water** to meet people's needs (measured per person per year).
What is water stress (Falkenmark)?
Supply **below 1 700 m3 per person per year** — demand begins to strain supply.
Physical vs economic scarcity?
**Physical** = the natural supply is too small (dry climate, low water table); **economic** = water exists but money/infrastructure stops people reaching it.
List the three Falkenmark thresholds.
Below **1 700 m3** = stress; below **1 000 m3** = scarcity; below **500 m3** = absolute scarcity (per person per year).
What is an aquifer?
An **underground rock store of groundwater**; over-abstraction is pumping it faster than it recharges.
What is over-abstraction and one impact?
Pumping groundwater faster than rainfall refills it; it causes the **water table to fall** (also subsidence, saltwater intrusion).
Name two physical causes of water scarcity.
Low/seasonal rainfall and drought (also rain shadow, falling water table, El Nino/La Nina, cold currents).
Name two economic causes of water scarcity.
Lack of money for pipes/pumps/dams and rising demand from population, cities and irrigation (also weak governance).
How does drought hit farming economically?
Crops fail and yields drop, so farmers lose income, food prices rise and people may migrate.
Give a named case of physical scarcity.
The **Sahel** of West Africa — low, erratic rainfall and recurring drought leave little surface water.
Give a named case of economic scarcity.
Much of **rural sub-Saharan Africa** — water exists but villages lack boreholes, pipes and funds to use it.
What does a top [10] scarcity essay need?
Developed physical AND economic causes, a named example for each, weighing by place/scale, and a clear judgement.
Topic 7.3 study notes
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