| Date | November 2018 | Marks available | 2 | Reference code | 18N.1.SL.TZ0.4 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Describe | Question number | 4 | Adapted from | N/A |
Question
Figure 8(a): River before and after beaver dam construction
Figure 8(b): Graphs to show nutrient and oxygen content in beaver pond and stream
(Error bars show standard deviation)
Figure 9(a): Fact file on beaver’s role in the ecosystem
- Beavers build dams with sticks, creating ponds and slowing the flow of rivers.
- Beaver ponds:
- are less suitable for river fish, for example brook trout
- provide new habitats for aquatic plants, for example bullhead lily, dragon fly larva, bullfrogs and
other fish, for example pearl dace.
- Dam may cause floods; if water covers the roots of river-edge trees, the trees may die and provide
more nesting sites for birds. - Marsh forms at the edge of beaver ponds.
- Grasses and sedges colonise the nutrient-rich silt at the bottom of the former pond, creating a beaver
meadow. - Beaver meadows have more light penetration, higher soil moisture, more nitrogen and a different
vegetation from that of the adjacent river-edge forest. - Dams may collapse because of heavy rains or spring melt, or if beaver is killed by a predator.
© International Baccalaureate Organization 2018
Figure 9(b): The succession of ecosystems caused when a beaver dam is built across a river
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.
With reference to Figures 9(a) and 9(b), explain the impacts of beaver dams on biodiversity within Algonquin Provincial Park.
Markscheme
This question requires “Resource Booklet - Nov 2018 SL paper 1”, available under the "your tests" tab > supplemental materials.
Award [1 max] for changes in ONE nutrient:
amount of carbon in sediments is 5 % higher in ponds/after construction of the dam / carbon is 20% in pond and 15% in stream;
concentration of phosphate is higher by 1.1 mg kg–1 in ponds/after construction of the dam / phosphate concentration is about 1.15mg kg–1 in the pond compared to about 0.05mg kg–1 in both streams;
concentration of nitrate is higher by 0.75 mg kg–1 in ponds / nitrate concentration in pond is 2 mg kg–1 compared to 1.25mg kg–1 upstream/site A / nitrate concentration in pond is 2 mg kg–1 compared to 0.25mg kg–1 downstream/site C.
Award [1 max] for changes in oxygen:
concentration of dissolved oxygen is lower by 9 ppm in ponds / oxygen concentration in pond is 3ppm compared to 12 ppm upstream/downstream/after construction of the dam.
Note: Figures do not need to be exact for nitrates or phosphates but some quantification is required.
Do not accept phosphate levels are negligible.
This question requires “Resource Booklet - Nov 2018 SL paper 1”, available under the "your tests" tab > supplemental materials.
dams reduce stream velocity/water flow creating ponds/marshes/additional habitat diversity / beaver ponds create new habitats for different aquatic plants (which increases plant diversity);
dam could reduce (diversity of) river fish species / cause loss of brook trout species;
dams lead to loss of trees/terrestrial vegetation from flooding (reducing species diversity);
as flooded trees die more nesting sites are provided for birds (increasing species diversity);when flooded trees die it decreases habitat availability for some organisms reducing species diversity;
low levels of oxygen in the resultant pond could reduce fish diversity/aquatic species diversity;
succession in meadow after dams collapse results in greater habitat diversity / when dams collapse, beaver meadows create habitats which differ from the surrounding forest.
Accept other reasonable responses.
Do not accept only “trees die / speciation”.
Examiners report
Responses varied widely with some good answers. A common error was to state only the amount of nutrients or oxygen levels within the pond and not give comparison values. Some candidates incorrectly read the values on the graph or did not give any values at all within their response.
This question was well answered with a significant number of students achieving full marks.
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.TZ0.6a:
Define biochemical oxygen demand (BOD).
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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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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.
