Distinguish between a pyramid of numbers and a pyramid of productivity.

Explain how three pollution management strategies may reduce eutrophication in agricultural areas.

Discuss with reasons or evidence, the environmental impacts of two named food production systems.

Award [2 max] for each pyramid type

pyramid of numbers:
displays the numbers of individuals/population size at each trophic level of a food chain/ecosystem;
may differ greatly in shape / may be inverted (depending on eg size of organisms/time of year/reproductive strategies);
represents storages;
represents quantities present at a given moment/snapshot in time; [2 max]

pyramid of productivity:
represents the gain in biomass/flow of energy at each level;
is measured in units of g/m2/yr or J/m2/yr;
tends to be pyramid-shaped;
represents flows;
represents rates/changes over a period of time; [2 max]

Award [1 max] for a diagram showing differing shape of pyramids of numbers v productivity for the same named food chain/ecosystem.

[4 max]

Award [1 max] for each of three strategies and [1 max] for accompanying explanation:

Strategy:
use organic fertilizers/manure/animal waste on agricultural fields;
Explanation:
this should reduce runoff/amounts of nitrates/phosphates;

Strategy:
legislate in favor of organic farming, / setting water quality standards;
Explanation:
would prevent unsustainable/polluting practices / overuse of agrochemicals;

Strategy:
legislate for/encourage restraint in use of artificial fertilizers/phosphate-rich detergents;
Explanation:
this will reduce quantity of nitrates/phosphates released into environment;

Strategy:
practice mixed cropping/crop rotation;
Explanation:
this will reduce the need for artificial fertilizers;

Strategy:
planting buffer zones around agricultural fields;
Explanation:
This helps absorb the excess nitrates/phosphates before they reach water bodies;

Strategy:
effective sewage treatment of urban waste;
Explanation:
this removes the excess phosphates and nitrates from the sewage before it reaches the water bodies;

Strategy:
safe collection of slurry from livestock farms;
Explanation:
prevent nitrates/phosphates from reaching water bodies/this will reduce concentrations of nitrates/phosphates in water bodies;

Strategy:
control application of fertilizers to times/seasons where run-off will be minimum;
Explanation:
this will reduce quantity of nitrates/phosphates entering water bodies; 

Strategy:
mud-pumping/removal of nutrient-rich sediment/bottom sediment from affected water bodies;
Explanation:
this will prevent ongoing release of nutrients/eutrophication;

Strategy:
introduce surface plants to take up excess nutrients;
Explanation:
this will reduce quantity of nitrates/phosphates in the water bodies;

Accept other reasonable responses of equivalent validity, relevance and significance.

[6 max]

Outline of impacts:
Award [3 max] if examples are not specifically named

Example 1: eg intensive wheat/corn production in USA:
using large quantities of herbicide/pesticides/agrochemicals reduces the biodiversity in surrounding areas/locally / eg may kill off many useful insects;
agrochemicals may affect top predators/birds through biomagnification/bioaccumulation / will intoxicate soils / kill soil invertebrates;
using a GMO (genetically modified organism) crop (eg Bt corn) reduces biodiversity;
heavy use of artificial/inorganic fertilisers may cause eutrophication of local water bodies;
use of agrochemicals/over-cultivation/heavy machinery may lead to loss of soil quality/compaction/salinization/toxification;
heavy irrigation/use of agrochemicals may lead to depletion/pollution of aquifers/water reservoirs;
irrigation/leaving fields bare after harvesting may lead to soil erosion; [2 max]

Example 2: eg cattle farming in Brazil:
land clearance/deforestation of tropical rainforest/cerrado vegetation results in loss of habitat/biodiversity / reduces a major global carbon sink/storage increasing global warming;
use of agrochemicals/pesticides/antibiotics leads to pollution of local habitats/loss of biodiversity;
displacement of indigenous people and their way of life reduces stewardship of local environment;
deforestation and overgrazing of the cattle increases soil erosion/desertification;
methane production by cattle contributes to global warming; [2 max]

Counterarguments and balancing factors relating to either or both systems:
impacts of inorganic fertilisers can be reduced/prevented by use of buffer zones;
use of agrochemicals/GM/intensive technology can increase yields per area reducing land required for food production;
drip irrigation technology can be used on a commercial scale to reduce water consumption;
GMO crops may be pest-resistant reducing need for pesticides;
crop-farming is ecologically more efficient than meat production (cattle farming);
cattle farming on Brazil has greater global impact than wheat farming in USA through its significant contribution to global warming;
tropical rainforest has particularly high biodiversity and so deforestation there causes a greater biodiversity loss; [4 max]

Award [1 max] for an explicit and valid conclusion.
Alternative points of equivalent validity, significance and relevance to those given, should be credited.
ie award [7 max] for marking points above, and [1 max] for a clear conclusion.

[8 max]

The majority of candidates were able to distinguish one to two points between the pyramids. A few confused the pyramids or mentioned a pyramid of biomass rather than productivity. A significant number wrote that a pyramid of productivity is never inverted, which is untrue.

Many candidates started the answer with a detailed description of eutrophication, which did not gain marks. The candidates mainly managed to give three clear strategies, however the weakest part was explaining how these strategies reduce eutrophication. Often the candidates gave confusing or vague answers. The answers to this question often illustrated how the candidates see the content in the question and then write an answer about that. So not answering the question asked at all.

Many candidates gave very vague examples of food production systems, thus limiting the marks they could receive. The other area of concern with this question was candidates only writing about the environmental impacts of the two systems. The counter arguments and balancing factors were only really attempted by the strongest candidates.