Outline the procedures in a laboratory-based method to find the gross productivity for a population of named aquatic animals in terms of biomass per day.

Explain how acid deposition falling on a forest may impact a nearby aquatic ecosystem.

When harvesting is limited to the sustainable yield, associated processes involved in a food production system may still make the production unsustainable.

In this context, to what extent can aquatic food production systems be truly sustainable?

find the dry weight of food presented to the population at start;
collect and find the dry weight of food remaining after a number of days;
subtract the weight of food remaining from that presented / find dry weight of food eaten;
collect and find the dry weight of feces produced over this period;
subtract weight of feces from food eaten to find food absorbed/gross productivity / food eaten − fecal loss = gross productivity;
divide final weight/gross productivity by number of days of the study;

Do not credit reference to weighing organisms (only relevant in net productivity).

run-off/groundwater flow may carry acidity directly to water body;
acidity/low pH may directly reduce survival of sensitive species;
reduced productivity of aquatic plants reduces food for higher trophic levels;
acidity in soils will release/leach cations/metal ions from soil particles;
aluminium/metal ions released from soil will enter water body;
aluminium ions may affect gills of fish reducing their survival;
other metal ions (cadmium) may be more toxic/lethal;
acidity reduces solubility of nutrients (e.g. N, P) so less nutrients leach/flow into aquatic system;
loss of trees/terrestrial/riparian vegetation may lead to erosion of soil into water body/reduced shade/increased temperatures;
more soil entering water body will increase turbidity;
high turbidity may lead to reduced photosynthesis/lower productivity;
all these impacts will lead to loss of biodiversity/low productivity;
forest soil may be alkaline reducing acidity of impact on aquatic system;

Only credit impacts on aquatic system, not impacts solely affecting forest.

Refer to paper 2 markbands, available under “your tests”  tab > supplemental materials.

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:

• understanding concepts and terminology of harvesting wild populations, capture fisheries, quotas, maximum sustainable yield, net productivity, fish stocks, overfishing, aquaculture, eutrophication, aquatic pollution, habitat loss, marine protection/exclusion zones, commercial vs. subsistence FPSs, etc.;
• breadth in addressing and linking aquaculture with unsustainable impacts e.g. eutrophication from excess feed/fecal deposits, genetic degradation of wild populations through escapees, pollution with medication, and means of reducing impacts e.g. polyculture, biological pest control, etc. and wild fishing with unsustainable impacts e.g. overfishing, capture of other species/immature individuals, lost nets/gear, water pollution due to mechanization, fossil fuel use, etc. and means to reduce impacts e.g. quotas, legislation on mesh size, seasonal limits, exclusion zones, possible miscalculation of MSY, etc.;
• examples of unsustainable impacts from aquaculture e.g. anti-fouling agents; antibiotics; excess feed, medicines, genetic modification, escapees, disease, etc. and fishing e.g. trawling, physical damage to e.g. corals/sedentary species, mesh size, bycatch, lost fishing gear, etc.;
• balanced analysis of degree to which collateral impacts of aquaculture/capture fisheries through mechanization, fossil fuel use, etc. can be sustainably managed including counterarguments, etc.;
• a conclusion that is consistent with, and supported by, analysis and examples given e.g. “a great deal can be done through legislation and choice of appropriate strategies to move aquatic food production toward true sustainability but ultimately certain unsustainable impacts are inevitable”;

The majority of candidates scored little, if anything, for this question as they confused gross with net secondary productivity and hence described strategies of finding dry weight of organisms that was unnecessary. Those that recognised the concept as being 'dry weight of food absorbed' found it easy to identify a method by subtracting dry weight of faecal loss from that of food eaten.

Many candidates scored some credit here, identifying the run-off into water bodies damaging plants and animals and leading to loss of biodiversity. Few considered more widespread impacts of soil erosion, release of aluminium, impact on nutrients, etc.

Many candidates could identify some ways in which the process of harvesting or farming of fish could be unsustainable even with application of maximum sustainable yield. There were also several very thorough responses to this question which considered multiple factors.