Identify four characteristics of ecosystems that contribute to their resilience.

Explain how positive feedback mechanisms may influence the equilibrium of an aquatic ecosystem during the process of eutrophication.

Pollution management strategies may be aimed at either preventing the production of pollutants or limiting their release into ecosystems.

With reference to either acid deposition or eutrophication, evaluate the relative efficiency of these two approaches to management.

biodiversity (genetic/species/habitat diversity);
diversity/complexity of interactions/linkages between components/developed food webs/nutrient cycling/establishment of keystone species;
size of storages/population sizes / abundance of resources;
presence of negative feedback mechanisms;
position of tipping points/thresholds of change;
maturity/later stage of succession/climax community;
balance of inputs and outputs / steady state equilibrium.

Award [1] for each correct characteristic identified, up to [4 max].
Do not accept responses that simply state “storages” or “tipping points”, all systems have these. It is the size or position of the storage or tipping point respectively that determines its resilience. Simply stating “biodiversity”, however, is acceptable because it is inherently quantitative.
Do not accept responses referring to low human interference, etc. Reduced disturbance may lead to more stable ecosystems, but it does not influence their resilience as such (ie their inherent ability to resist disturbance).

in eutrophication, positive feedback amplifies changes in the system and drives it toward a tipping point;
…when a new equilibrium is adopted with low diversity/loss of species/dominance of algae;

Award [5 max] for marking points given above (including each of those in a box on the diagram) or up to [7 max] if the processes identified complete a genuine loop of positive feedback ie where a given change promotes further change of same process.

The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria given in each of the markbands (although “ESS terminology” has been conflated with “Understanding concepts”). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.

Answers may include:

For Eutrophication:

• understanding concepts and terminology of eutrophication, distinction between prevention and limiting management strategies, inorganic nutrients, phosphate-free detergents, organic vs inorganic fertilizers, organic farming, domestic and agricultural waste, sewage treatment, N/P stripping, buffer zones, point vs non-point sources, etc
• breadth in addressing and linking a range of strategies with their effectiveness in reducing impacts of pollutants, from different sources, on different ecosystems, and their relevance and validity for different societies, etc
• examples of prevention strategies (changing human activity) eg alternative fertilisers, P-free detergents, and limiting strategies eg N/P stripping phase in water treatment, use of buffer zones, in named case studies/societies, etc
• balanced analysis of the relative efficiency of the two approaches in reducing impacts on ecosystems; meeting needs of societies, cost and ease of application, etc
• a conclusion that is consistent with, and supported by, analysis and examples given eg generally, prevention strategies are more efficient because they are directed at the root of the problem, but limiting strategies may be seen as more appropriate from an anthropocentric/technocentric perspective as they will be of less hindrance to productivity

For Acid Deposition:

• understanding concepts and terminology of acid deposition, distinction between prevention and limiting management strategies, NOx and SOx, atmospheric emissions, fossil fuels, biodiesel, alternative energy, cement/pulp and paper industries, etc
• breadth in addressing and linking a range of strategies with their effectiveness in reducing impacts of pollutants, from different sources, on different ecosystems, and their relevance & validity for different societies, etc
• examples of prevention strategies (changing human activity) eg using alternative energy sources, eg solar, hydro, wind, etc, energy saving technology, transport bans/public transport, paper recycling, and limiting strategies eg scrubbers, catalytic converters, etc
• balanced analysis of the relative efficiency of the two approaches in reducing impacts on ecosystems, meeting needs of societies, cost and ease of application, etc
• a conclusion that is consistent with, and supported by analysis and examples given eg “Generally, prevention strategies are more efficient because reducing the use of fossil fuels will simultaneously resolve many other environmental impacts of using this resource which ultimately will become unavailable.”

If response addresses both acid rain and eutrophication, only award marks for the higher scoring topic.

Refer to paper 2 markbands, available under the "your tests" tab > supplemental materials.

Question 5 was a popular choice. The majority could identify biodiversity as a factor contributing to resilience; other factors were less commonly listed or too vague/confused to gain credit.

A very significant majority were able to gain over half the available marks through a description of eutrophication. Few were able to demonstrate a complete and valid positive feedback loop, commonly seeing it as just an ongoing process with lots of impacts (no feedback).

Responses were very generally quite poor with the vaguest of strategies, e.g. ‘banning the pollutant’; ‘limiting the use of the pollutant’. Also, many responses failed to make a clear/valid distinction between preventative and limiting strategies.