| Date | November 2016 | Marks available | 1 | Reference code | 16N.1.SL.TZ0.6 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Define | Question number | 6 | Adapted from | N/A |
Question
Figure 6: The effects of organic pollution (raw sewage discharged from a pipe) on a stream ecosystem.
[Source: Dr. Mel Zimmerman, Professor of Biology and Director of Clean Water Institute at Lycoming College. Adapted from Bartsch and Ingram (1975) ]
Define biochemical oxygen demand (BOD).
Outline how turbidity changes after the raw sewage discharge point in Graph B.
Suggest how the population growth curve for algae in Graph C would appear if the pollutant had been nitrates and phosphates from fertilizer run-off.
Outline why point source pollution is often easier to manage than non-point source pollution.
Markscheme
a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity.
OWTTE.
[1 max]
after the point of sewage discharge the turbidity levels rise until about 150m (accept 125-175m) downstream where levels peak/plateau and thereafter steadily decline;
turbidity will increase at the point sewage enters the water, as the pollutant is particulate/coloured;
turbidity will increase after the outlet of sewage as bacteria grow rapidly as they consume/decompose the sewage;
turbidity remains high as algae now rapidly grow as there are nutrients from the sewage decomposition available;
turbidity decreases once the nutrients levels fall to the pre-sewage levels and the algae growth declines;
turbidity increases as algae decrease, and then decrease as algae increase.
Award 1 max for a clear description of change in turbidity levels along the stream.
[2 max]
increase in nutrients will lead to rapid algae growth /could cause algal bloom;
algae levels will decline as nutrient levels become more restricted downstream from the source;
algae would look like the microorganisms curve in the diagram/ rapidly go up right after the pollution outlet;
algae would also decline, like the microbe curve, as the nutrients run out and algae start to die;
microbes would grow and they could shade out the light for algae causing a further drop in the curve;
the trend observed would be opposite to the current growth curve for algae (on graph C).
Only credit responses that refer to algae levels in Graph C, do not credit descriptions of eutrophication.
[3 max]
point source can be clearly identified;
so pollution can be more easily monitored;
solutions should be more easily applied / pollution can be stopped directly;
with non-point pollution, source is widespread/dispersed and difficult to identify;
solutions also have to be widespread/dispersed, so there are increased costs/difficulties of monitoring;
compliance is difficult to ensure with non-point pollution because of widespread/dispersed nature of sources.
[2 max]
Examiners report
Very few students were able to provide a comprehensive definition of biochemical oxygen demand.
Most students achieved a mark for describing changes in turbidity level along the stream. Few candidates were able to explain the cause of turbidity or give reasons for the changing levels.
Most candidates achieved some marks for this question but few achieved the full 3 marks. Many responses overly discussed eutrophication without reference to the curve.
This question was answered well by most students.
Syllabus sections
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19M.2.SL.TZ0.6b:
Suggest a range of practical procedures that could be carried out to measure the abiotic and biotic impacts of an oil spill in an aquatic ecosystem.
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19M.1.SL.TZ0.11a:
Explain how the following land-based activities could have a damaging effect on marine ecosystems within the Coral Triangle: deforestation.
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19N.1.SL.TZ0.5:
With reference to information in the resource booklet, evaluate the sustainability of Canada’s management of the Large Ocean Management Area of the St Lawrence River estuary and Gulf of St Lawrence.
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15M.2.SL.TZ0.1c.ii:
Identify one possible pollution management strategy for Inle Lake in each of the categories in the table below.
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18N.2.SL.TZ0.5c:
Discuss strategies that can be used to improve the sustainability of food production systems.
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17M.2.SL.TZ0.4c:
To what extent are the concepts of net productivity and natural income useful in managing the sustainable harvesting of named resources from natural ecosystems?
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15M.2.SL.TZ0.1a.iii:
With reference to Figures 4 and 5, identify three environmental impacts that may occur as a consequence of human activities on and around Inle Lake.
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17M.2.SL.TZ0.6c:
The provision of food resources and assimilation of wastes are two key factors of the environment that determine its carrying capacity for a given species.
To what extent does the human production of food and waste each influence the carrying capacity for human populations?
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15M.2.SL.TZ0.1c.iii:
Explain how the use of fertilizers in agriculture may lead to hypoxic water in the areas shown in Figure 7.
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18M.1.SL.TZ0.10:
Explain how the protection of forests in Makira National Park may contribute to the conservation of the aquatic environment of MaMaBay.
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19N.1.SL.TZ0.4a:
Using Figure 11(b), estimate the highest concentrations of coliform bacteria (in units/100 mL) found in the St Lawrence River one day after the untreated sewage was released.
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19M.1.SL.TZ0.11b:
Explain how the following land-based activities could have a damaging effect on marine ecosystems within the Coral Triangle: agricultural activity.
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19M.1.SL.TZ0.8:
With reference to Figure 5, describe how loss of a coral reef ecosystem could impact a neighbouring seagrass community.
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19N.2.SL.TZ0.8b:
Explain how environmental indicators are used to assess sustainability.
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19N.1.SL.TZ0.3b:
With reference to Figure 9(a), outline how the round goby both positively and negatively affects the St Lawrence River ecosystem.
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19N.2.SL.TZ0.7c:
To what extent do the approaches and strategies of different environmental value systems improve access to fresh water?
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19N.2.SL.TZ0.6b:
Explain how ecological techniques can be used to study the effects of human activities on the biodiversity of a named ecosystem.
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19N.2.SL.TZ0.5c:
To what extent is pollution impacting human food production systems?
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19N.1.SL.TZ0.4c:
With reference to Figures 10, 11(a) and 11(b), describe a method to monitor the impact of the release of untreated sewage into the St Lawrence River ecosystem.
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18N.2.SL.TZ0.6c:
Discuss the consequences of changing global per capita meat consumption on the conservation of ecosystems and biodiversity.
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14M.2.SL.TZ0.5b:
Evaluate the use of biotic indices compared with direct methods of measuring pollution.
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15M.2.SL.TZ0.5a:
Outline two indirect methods that could be used to measure the impact on the river ecosystem of dead organic matter from the flooded vegetation and soils.
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15N.1.SL.TZ0.5c:
Apart from global warming and ozone-depletion, state one pollution problem that may affect a number of countries.
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16N.1.SL.TZ0.6c:
Suggest how the population growth curve for algae in Graph C would appear if the pollutant had been nitrates and phosphates from fertilizer run-off.
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18N.1.SL.TZ0.4a:
With reference to Figures 8(a) and 8(b), describe the changes in nutrient and oxygen content that occur after beaver dams are constructed. Include quantities in your response.
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17M.2.SL.TZ0.5b:
Explain how positive feedback mechanisms may influence the equilibrium of an aquatic ecosystem during the process of eutrophication.
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14N.2.SL.TZ0.3b:
Explain how three pollution management strategies may reduce eutrophication in agricultural areas.
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16N.2.SL.TZ0.4b:
Explain two factors which lead to a loss of marine (ocean) biodiversity.
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16M.1.SL.TZ0.2a.v:
Nitrates and phosphates from nearby farms may drain into the lake. Identify a strategy for managing this pollution at each of the following levels:
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16N.2.SL.TZ0.1l:
Using evidence from the resource booklet, justify from an ecocentric viewpoint why the Husab Uranium Project should not be approved.
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17N.1.SL.TZ0.3c:
With reference to Figures 6(c), 7(a) and 7(b) explain the problems associated with land restoration in Iceland.
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18M.2.SL.TZ0.6b:
Explain how organic waste may be an effective fertilizer in terrestrial systems but a source of pollution in aquatic systems.
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19N.1.SL.TZ0.4b:
Outline an environmental problem that may result from the release of untreated sewage into a river.
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17M.2.SL.TZ0.5c:
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.
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16N.1.SL.TZ0.6b:
Outline how turbidity changes after the raw sewage discharge point in Graph B.
