Types and sources of water pollution
Big idea: Water pollution comes from point sources (easy to identify, like a factory pipe) and non-point sources (spread across the landscape, like farm runoff). Non-point sources are harder to control!
Point vs non-point sources
Point sources
- Single, identifiable location
- Examples: factory discharge, sewage pipes, oil spills
- Easier to regulate and control
- Can be treated at source
Non-point sources
- Diffuse, spread across landscape
- Examples: agricultural runoff, urban stormwater, atmospheric deposition
- Very difficult to regulate
- Requires landscape-level management
Major types of water pollutants
- Nutrients - nitrates, phosphates from agriculture and sewage (cause eutrophication)
- Pathogens - bacteria, viruses from sewage (cause disease)
- Organic matter - reduces dissolved oxygen as it decomposes
- Heavy metals - mercury, lead, cadmium (toxic, bioaccumulate)
- Synthetic chemicals - pesticides, industrial chemicals, pharmaceuticals
- Thermal pollution - heated water from power plants (reduces oxygen)
- Plastics - especially microplastics (persist, enter food chains)
- Sediment - soil erosion clouds water, smothers habitats
Paper 1 tested this! Outline two reasons why nutrient pollution in the Gulf of Mexico is difficult to manage. Key: it is NON-POINT source (from huge drainage basin), agriculture is economically important, source is far from impact zone.
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IB-style question — point vs non-point pollution sources [4]
A river runs past a paper mill and through farmland. The mill releases waste from one outflow pipe; the farms lose fertiliser from many fields after rain.
Using these examples, distinguish between point sources and non-point (diffuse) sources of water pollution. [4]
How to answer it, step by step
- Point source = one clear spot
• Comes from one place you can find, like the mill's outflow pipe.
• Easy to control because you only have to manage that one pipe. - Non-point source = spread out
• Comes from many places at once, like fertiliser washing off lots of farm fields.
• Hard to control because you cannot point to a single cause.
Final answer
Always give a named example for each type — 'distinguish' answers lose a mark with no examples.
IB-style question — pollutant build-up up a food chain [2]
In a lake food chain, water fleas hold 200 units of energy and the small fish that eat them hold 18 units.
(i) Calculate the percentage energy transfer from water fleas to small fish. [1]
(ii) A pesticide (a POP) is measured at higher concentrations in the small fish than in the water fleas. State the relationship between POP concentration and trophic level. [1]
How to answer it, step by step
- (i) Energy transfer %
• Formula: (energy at higher level ÷ energy at lower level) × 100.
• (18 ÷ 200) × 100 = 9%. - (ii) POPs and trophic level
• As you go up the food chain, POP concentration goes up too.
• So it is a positive (direct) relationship.
Final answer
For the relationship part just state 'increases / positive' — do NOT write 'biomagnification', that word is not credited here.