Cambridge IGCSE · Thinka-original Practice Paper

2024 Cambridge IGCSE Environmental Management (0680) Practice Paper with Answers

Thinka Jun 2024 (V1) Cambridge International A Level-Style Mock — Environmental Management (0680)

160 marks210 mins2024

An original Thinka practice paper modelled on the structure and difficulty of the Jun 2024 (V1) Cambridge International A Level Environmental Management (0680) paper. Not affiliated with or reproduced from Cambridge.

Paper 11 Section A

Answer all short-answer questions. Write your answers in the spaces provided.

4 Question · 20 marks

Question 1 · Short Answer & Recall

5 marks

Explain how both minimum net mesh sizes and closed seasons are used to manage the harvesting of marine species sustainably.

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Worked solution

Minimum net mesh sizes:
- Allows small and juvenile fish to escape through the gaps in the net.
- This ensures young fish reach sexual maturity and reproduce before they are harvested, sustaining future populations.

Closed seasons:
- Fishing is banned during specific times of the year, particularly during spawning/breeding seasons.
- This protects adult fish while they are reproducing and prevents disruption to nesting or spawning grounds.
- It allows fish populations to recover and replenish without human harvesting pressure.

Marking scheme

Award up to 3 marks for explanation of minimum net mesh sizes:
- allows smaller/juvenile fish to escape / pass through the net [1]
- allows fish to reach sexual maturity/breeding age [1]
- maintains sustainable breeding populations / prevents recruitment overfishing [1]

Award up to 3 marks for explanation of closed seasons:
- restricts/bans fishing during breeding or spawning seasons [1]
- protects spawning adults / pregnant individuals [1]
- allows fish populations to recover/replenish undisturbed [1]

Max 5 marks total.

Question 2 · Short Answer & Recall

5 marks

Describe how tectonic plates move to cause earthquakes at conservative plate boundaries, and explain why earthquakes at these boundaries can cause high levels of damage.

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Worked solution

Mechanism:
- Two tectonic plates slide past each other, either in opposite directions or in the same direction at different speeds.
- Friction causes the plate margins to become locked or snagged.
- Stress and pressure build up over time as the plates continue to try to move.
- The stress suddenly overcomes the friction, releasing energy as seismic waves from the shallow focus.

Why damage is high:
- Earthquakes at conservative boundaries are typically shallow-focus earthquakes.
- Shallow focus means seismic waves travel a shorter distance to the surface, retaining more energy and causing much more violent ground shaking.

Marking scheme

Award up to 3 marks for describing plate movement at conservative boundaries:
- plates slide past each other / move in opposite directions / same direction at different speeds [1]
- plates become locked/snagged due to friction [1]
- pressure/tension builds up [1]
- sudden release of energy/seismic waves when plates slip [1]

Award up to 2 marks for explaining high damage:
- earthquakes have a shallow focus [1]
- seismic waves lose less energy before reaching the surface / causing more violent ground shaking [1]
- conservative boundaries often occur on land/near populated areas [1]

Max 5 marks total.

Question 3 · Short Answer & Recall

5 marks

Explain why only a small percentage of energy is transferred from one trophic level to the next in a food chain, and state how this energy loss limits the total number of trophic levels.

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Worked solution

Energy loss mechanisms:
- Energy is lost as heat to the environment during respiration.
- Energy is used for active movement and metabolism of the organism.
- Some energy is lost in waste products (excretion and egestion, such as faeces and urine).
- Not all parts of an organism are eaten or digested (e.g., bones, claws, roots).

Limitation on trophic levels:
- Because only approximately \(10\%\) of energy is transferred to the next level, the total available energy decreases rapidly.
- By the 4th or 5th trophic level, there is insufficient energy left to support a viable population of tertiary or quaternary consumers.

Marking scheme

Award up to 4 marks for explaining reasons for energy loss:
- energy lost as heat [1]
- lost through respiration [1]
- lost through movement / metabolic processes [1]
- lost in excretion / egestion / faeces / waste [1]
- not all parts of the organism are consumed/digested [1]

Award up to 2 marks for explaining the limit on trophic levels:
- energy decreases rapidly at each step / only approx. \(10\%\) transferred [1]
- at higher levels, there is not enough energy remaining to support another population/trophic level [1]

Max 5 marks total.

Question 4 · Short Answer & Recall

5 marks

Describe how geothermal energy is harnessed to generate electricity, and state two environmental advantages of geothermal power compared to coal-fired power stations.

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Worked solution

How geothermal electricity is generated:
- Cold water is pumped down injection wells into deep, hot underground rocks.
- The hot rocks heat the water, turning it into superheated steam.
- The steam rises up a production well under high pressure.
- The steam spins a turbine, which is connected to a generator that produces electricity.

Environmental advantages over coal:
- No/minimal greenhouse gases (CO2) released during operation, reducing contribution to global warming.
- No sulfur dioxide (SO2) or nitrogen oxides (NOx) emitted, reducing acid rain.
- No particulate matter/smoke/soot released, improving air quality.
- No land-based mining required (which causes habitat destruction/waste heaps).

Marking scheme

Award up to 3 marks for describing generation:
- water pumped down into hot underground rocks [1]
- water heated/converted to steam [1]
- steam turns/drives a turbine [1]
- turbine drives/powers a generator [1]

Award up to 2 marks for environmental advantages (must compare to coal directly or by implication):
- does not release carbon dioxide / does not contribute to global warming [1]
- does not produce sulfur dioxide / nitrogen oxides / does not cause acid rain [1]
- does not produce ash/soot/air pollution/particulates [1]
- less habitat destruction compared to coal mining [1]

Max 5 marks total.

Paper 11 Section B

Answer all structured and evaluation-style questions. Show all working where calculations are required.

4 Question · 60 marks

Question 1 · Structured

15 marks

A fishing community relies on marine catches. However, global fish stocks have declined. (a) Suggest three reasons why international agreements like exclusive economic zones (EEZs) are difficult to enforce. (b) Explain how the following conservation methods help manage fish stocks sustainably: (i) net mesh size restrictions, (ii) quotas, and (iii) closed seasons. (c) A local fishery had an annual cod catch limit of 12,000 tonnes in 2020. Due to dwindling populations, the quota was reduced to 8,400 tonnes for 2021. (i) Calculate the percentage decrease in the quota. Show your working. (ii) Describe four challenges of monitoring marine fishing activities far out at sea.

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Worked solution

(a) EEZs are difficult to enforce because: 1. Oceans are vast and difficult to patrol with limited coastguard vessels. 2. High cost of surveillance and radar equipment. 3. Disputes over boundary lines between neighbouring countries. (b) Conservation methods: (i) Net mesh size restrictions allow juvenile fish to escape and grow to breeding age, maintaining the population. (ii) Quotas limit the total weight of fish caught, preventing overfishing beyond sustainable yield. (iii) Closed seasons ban fishing during breeding periods, allowing fish to reproduce undisturbed. (c)(i) Decrease = \( 12,000 - 8,400 = 3,600 \) tonnes. Percentage decrease = \( \frac{3,600}{12,000} \times 100 = 30\% \). (c)(ii) Challenges of monitoring: 1. Extreme weather conditions. 2. Flags of convenience used by illegal vessels. 3. High financial cost of tracking systems like VMS. 4. Corrupt officials or lack of international cooperation.

Marking scheme

(a) [3 marks] 1 mark for each valid reason, e.g., vast ocean areas to patrol, lack of financial resources/vessels, boundary disputes. (b) [6 marks] (i) 2 marks: allows small/young fish to escape (1), so they can reach reproductive maturity (1). (ii) 2 marks: sets a legal limit on catch (1), preventing depletion of stocks beyond safe biological limits (1). (iii) 2 marks: protects fish during spawning seasons (1), ensuring recruitment of new cohorts (1). (c)(i) [2 marks] 1 mark for correct calculation of change (3,600) or correct formula, 1 mark for correct final answer (30%). (c)(ii) [4 marks] 1 mark for each valid challenge, up to 4: e.g., vastness of oceans, high cost of marine patrols, vessels disabling transponders, flags of convenience, or corruption.

Question 2 · Structured

15 marks

Volcanoes and earthquakes present major risks. (a) Explain why some volcanic eruptions are highly explosive while others are relatively gentle. (b) State three tectonic settings where volcanoes are typically found. (c) Describe three methods used by volcanologists to monitor active volcanoes in order to predict eruptions. (d) In 2021, an island volcano erupted, displacing 12,500 people. (i) Calculate the percentage of the island's total population of 80,000 that was displaced. Show your working. (ii) Evaluate the effectiveness of post-disaster aid compared to long-term hazard-resistant infrastructure in reducing earthquake deaths in developing nations.

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Worked solution

(a) Volcanic explosivity depends on magma composition: high-silica (viscous) magma traps gases, building up immense pressure leading to explosive eruptions, whereas low-silica (runny/basaltic) magma allows gases to escape easily, resulting in gentle, effusive eruptions. (b) Tectonic settings: 1. Divergent boundaries (mid-ocean ridges). 2. Convergent boundaries (subduction zones). 3. Hotspots (mantle plumes). (c) Monitoring methods: 1. Seismometers to detect earthquakes caused by magma movement. 2. Tiltmeters to measure ground deformation as the volcano swells. 3. Gas sensors to monitor changes in sulfur dioxide and carbon dioxide emissions. (d)(i) Percentage = \( \frac{12,500}{80,000} \times 100 = 15.625\% \) (accept 15.6% or 15.63%). (d)(ii) Long-term hazard-resistant infrastructure (e.g., building codes, cross-bracing) is highly effective because it prevents building collapse, which is the primary cause of earthquake deaths. Post-disaster aid (medical help, food, search and rescue) is essential for survival after the event but cannot undo the initial high death toll from collapsed buildings. In developing nations, aid is often delayed by poor transport links, making preventative infrastructure much more effective in saving lives, although it requires high initial investment.

Marking scheme

(a) [3 marks] Mention of magma viscosity/silica content (1); trapped gases building up pressure in explosive eruptions (1); gas escaping easily in runny/basaltic lava for gentle eruptions (1). (b) [3 marks] 1 mark for each correct setting: convergent plate boundaries (1), divergent plate boundaries (1), hotspots (1). (c) [3 marks] 1 mark for each method with its purpose: seismometers/seismographs to detect tremors (1); tiltmeters/GPS to measure ground swelling (1); gas spectrometers to monitor gas composition/emissions (1). (d)(i) [2 marks] 1 mark for correct working: (12,500 / 80,000) * 100. 1 mark for correct answer: 15.625% / 15.6% / 15.63%. (d)(ii) [4 marks] Max 3 marks for describing one aspect only. Balanced evaluation: Infrastructure prevents initial deaths from collapses (1); post-disaster aid saves those trapped or injured but does not prevent the initial disaster (1); infrastructure is proactive while aid is reactive (1); developing nations face challenges funding infrastructure but aid can be delayed (1).

Question 3 · Structured

15 marks

Consider a temperate forest ecosystem. (a)(i) Outline the flow of energy through a typical food chain containing producers, primary consumers, secondary consumers, and tertiary consumers. (ii) Explain why only about 10% of the energy is transferred from one trophic level to the next. (b) Describe the role of decomposers in an ecosystem. (c) Human activities like deforestation disrupt global ecosystems and cycles. (i) Describe how trees are involved in the cycling of carbon. (ii) Suggest five consequences of global ecosystem disruption on human populations.

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Worked solution

(a)(i) Energy enters as sunlight and is fixed by producers (plants) via photosynthesis. It then flows to primary consumers (herbivores), secondary consumers (carnivores), and finally tertiary consumers (apex predators). (a)(ii) Energy transfer is inefficient because: 1. Some energy is lost as heat during respiration. 2. Not all parts of an organism are eaten (e.g., bones, woody stems). 3. Some material is undigested and lost as waste/feces. (b) Decomposers (like bacteria and fungi) break down dead organic matter and waste, releasing essential nutrients (like nitrogen and phosphorus) back into the soil, making them available again for producers. (c)(i) Trees absorb carbon dioxide from the atmosphere during photosynthesis and store it as carbon in biomass (organic compounds). They release carbon dioxide back to the atmosphere through respiration and when they die and decay. (c)(ii) Consequences on human populations: 1. Loss of potential medicines derived from wild plants. 2. Reduced food security due to loss of wild food sources and pollinators. 3. Increased flooding and soil erosion from loss of vegetation. 4. Disruption of water cycles leading to local droughts. 5. Increased greenhouse gases in the atmosphere leading to accelerated climate change and severe weather.

Marking scheme

(a)(i) [2 marks] Correct order of trophic levels (producer -> primary consumer -> secondary consumer -> tertiary consumer) (1); mention of energy coming from sunlight/photosynthesis (1). (a)(ii) [3 marks] 1 mark for each reason: energy lost as heat through respiration (1); energy lost in undigested waste/feces (1); not all parts of the organism are consumed (1). (b) [2 marks] Breakdown of dead organic matter/waste (1); recycling of nutrients back into the soil/ecosystem (1). (c)(i) [3 marks] Absorption of carbon dioxide via photosynthesis (1); carbon storage in biomass (1); release of carbon dioxide via respiration or decomposition (1). (c)(ii) [5 marks] 1 mark for each valid consequence, up to 5: e.g., loss of medicinal resources, decreased food security, loss of ecosystem services (e.g., pollination), increased flooding, soil erosion, water cycle disruption/drought, climate change impacts (extreme weather).

Question 4 · Structured

15 marks

Energy resources are crucial for modern life but carry environmental consequences. In a specific country, electricity is generated from: Coal (45%), Natural Gas (30%), Nuclear (12%), Hydroelectric (8%), and Wind & Solar (5%). (a)(i) Calculate the total percentage of electricity generated from non-renewable fossil fuels. (ii) Compare the environmental impacts of generating electricity from coal with generating electricity from nuclear power. (b) Explain how a hydroelectric power station generates electricity. (c) Solar energy is a popular renewable energy source. (i) State two advantages and two disadvantages of using solar energy on a large scale. (ii) Define the term 'intermittent' in the context of renewable energy sources.

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Worked solution

(a)(i) Fossil fuels are Coal and Natural Gas. Total percentage = \( 45\% + 30\% = 75\% \). (a)(ii) Coal power plants release greenhouse gases (carbon dioxide) contributing to global warming, and sulfur dioxide which causes acid rain. They also produce large amounts of ash waste. Nuclear power plants do not release greenhouse gases during operation, avoiding atmospheric pollution. However, nuclear power produces highly radioactive waste that requires secure, long-term storage, and carries a risk of catastrophic accidents releasing radiation into the environment. (b) Water stored behind a dam in a reservoir has potential energy. When released, gravity pulls the water down through tunnels (penstocks), converting potential energy to kinetic energy. This moving water turns a turbine, which spins a generator to produce electrical energy. (c)(i) Advantages: 1. Renewable and does not release greenhouse gases during operation. 2. Low maintenance costs once installed. Disadvantages: 1. High initial installation costs. 2. Large land area required for solar farms, potentially destroying local habitats. (c)(ii) 'Intermittent' means that the energy source is not continuously available and depends on external factors (such as weather, daylight, or wind speed) which are unpredictable.

Marking scheme

(a)(i) [1 mark] 75% (Coal 45% + Gas 30%). (a)(ii) [4 marks] Max 2 marks for coal: carbon dioxide / greenhouse gases causing global warming (1), sulfur dioxide causing acid rain (1). Max 2 marks for nuclear: produces radioactive waste that needs long-term storage (1), risk of nuclear accidents/radiation leaks (1). Award 1 mark for noting that nuclear does not emit greenhouse gases while coal does. (b) [4 marks] Water stored in reservoir has gravitational potential energy (1); water flows down pipes/penstocks turning potential to kinetic energy (1); kinetic energy of water spins a turbine (1); turbine drives a generator to produce electricity (1). (c)(i) [4 marks] 1 mark for each advantage (max 2): e.g., renewable/abundant, no greenhouse gas emissions, low operational costs. 1 mark for each disadvantage (max 2): e.g., high setup cost, requires large land area, depends on sunlight. (c)(ii) [2 marks] Energy production is not constant/reliable (1); it depends on environmental factors like sunlight/weather conditions (1).

Paper 21 Management in Context

Answer all questions. Use the resource information provided about New Zealand to apply your environmental management knowledge.

3 Question · 79.80000000000001 marks

Question 1 · Structured & Scenario Context

26.6 marks

### Context: Geothermal Energy and Volcanism in New Zealand

New Zealand's North Island is located on the active boundary of the Pacific and Indo-Australian tectonic plates. This plate boundary results in both tectonic hazards and significant opportunities, such as geothermal energy production.

**(a)(i)** Describe how tectonic plate movement leads to volcanic activity at subduction zones. [4]

**(a)(ii)** State two hazardous emissions, other than lava, released during a volcanic eruption. [2]

**(b)(i)** New Zealand generates approximately 18% of its electricity from geothermal resources. Explain how geothermal energy is used to generate electricity. [4]

**(b)(ii)** Suggest two environmental advantages and two environmental disadvantages of using geothermal energy compared to burning fossil fuels. [4]

**(c)** Volcanoes present both hazards and opportunities. Discuss how volcanic regions can benefit local economies and communities. [4]

**(d)** A student investigated geothermal soil temperatures at different distances from a hot spring in Rotorua. The results are shown in the table below:

| Distance from hot spring / m | Soil temperature / °C |
|---|---|
| 2 | 78 |
| 4 | 62 |
| 6 | 45 |
| 8 | 31 |
| 10 | 22 |

**(d)(i)** Describe how the student would plot these results on a grid. [2]

**(d)(ii)** Describe the relationship shown by the data. [1]

**(d)(iii)** Explain three ways the student could improve the reliability and safety of this investigation. [3.6]

Show answer & marking scheme

Worked solution

Detailed sub-question marking:
- (a)(i) [4 marks]: 1 mark for identifying convergent/colliding plates; 1 mark for subduction of the denser plate; 1 mark for melting of mantle/crust; 1 mark for magma rising through crust to form volcanoes.
- (a)(ii) [2 marks]: 1 mark for each valid emission (e.g., ash, sulfur dioxide, carbon dioxide, steam, pyroclastic flows). Reject: lava.
- (b)(i) [4 marks]: 1 mark for steam/hot water extracted from underground; 1 mark for high pressure; 1 mark for steam spinning a turbine; 1 mark for turbine driving an electrical generator.
- (b)(ii) [4 marks]: 2 marks for two valid advantages (renewable, low carbon footprint, space-efficient); 2 marks for two valid disadvantages (geothermal brine disposal, trace toxic gas emissions, site-specific nature).
- (c) [4 marks]: 1 mark for each distinct economic/community benefit discussed (e.g., fertile soils, tourism, geothermal energy, mineral extraction).
- (d)(i) [2 marks]: 1 mark for placing distance on x-axis and temperature on y-axis with correct units; 1 mark for specifying linear scales and accurate point plotting with line.
- (d)(ii) [1 mark]: 1 mark for identifying that temperature decreases as distance increases.
- (d)(iii) [3.6 marks]: 1 mark for a valid reliability improvement (averaging repeats); 1 mark for precision improvement (digital probe); 1.6 marks for a detailed safety precaution (heat-resistant gear, staying on marked tracks).

Marking scheme

Marking scheme breakdown:
- (a)(i) 4 marks: Convergent plate boundary (1), subduction of oceanic crust (1), melting to form magma (1), rising magma erupting through crust (1).
- (a)(ii) 2 marks: Two correct gases/pyroclastics (e.g., ash, SO2) (1+1).
- (b)(i) 4 marks: Steam/hot water harnessed (1) -> high pressure (1) -> spins turbine (1) -> drives generator to produce electricity (1).
- (b)(ii) 4 marks: 2 Advantages (renewable, low CO2) (1+1) and 2 Disadvantages (brine disposal, trace toxic gases) (1+1).
- (c) 4 marks: Four detailed benefits (tourism, fertile soils, geothermal heating, minerals) (1+1+1+1).
- (d)(i) 2 marks: X and Y axes allocation and labeling (1), plotting accuracy and line drawing (1).
- (d)(ii) 1 mark: Inverse relationship statement (1).
- (d)(iii) 3.6 marks: Repeats for average (1), digital apparatus (1), safety gear/safe distance protocols (1.6).

Question 2 · Structured & Scenario Context

26.6 marks

### Context: Marine Fisheries Management in New Zealand

New Zealand has one of the largest Exclusive Economic Zones (EEZ) in the world, spanning approximately 4.3 million square kilometers. To manage its fisheries sustainably, New Zealand introduced the Quota Management System (QMS) in 1986.

**(a)(i)** Explain the term *Exclusive Economic Zone (EEZ)*. [2]

**(a)(ii)** Describe how a Quota Management System (QMS) helps to prevent overfishing of marine species. [4]

**(b)** Besides quotas, state and explain three other methods used to manage marine fish stocks sustainably. [6]

**(c)** Marine protected areas (MPAs) are established around the coast of New Zealand.

**(c)(i)** Define the term *Marine Protected Area*. [2]

**(c)(ii)** Suggest how MPAs can benefit fish populations in adjacent, non-protected fishing zones. [3]

**(d)** An ecological survey of New Zealand snapper (*Pagrus auratus*) was conducted over five years to estimate population density (number of fish per \(100\text{ m}^2\)) inside and outside an MPA. The data is shown below:

* **Year 1:** Inside = 12, Outside = 8
* **Year 2:** Inside = 15, Outside = 7
* **Year 3:** Inside = 22, Outside = 6
* **Year 4:** Inside = 31, Outside = 8
* **Year 5:** Inside = 45, Outside = 9

**(d)(i)** Calculate the percentage change in the snapper population density inside the MPA from Year 1 to Year 5. Show your working. [3]

**(d)(ii)** Suggest why the snapper population outside the MPA did not show a continuous increase. [3]

**(d)(iii)** Explain why some commercial fishers might object to the creation of new MPAs. [3.6]

Show answer & marking scheme

Worked solution

Detailed sub-question marking:
- (a)(i) [2 marks]: 1 mark for the 200 nautical miles distance from coast; 1 mark for exclusive sovereign rights over resource exploitation/management.
- (a)(ii) [4 marks]: 1 mark for scientific stock assessment/TACC; 1 mark for dividing quotas into ITQs; 1 mark for legally limiting the total catch to sustainable limits; 1 mark for enforcement and penalization of breaches.
- (b) [6 marks]: 1 mark for naming and 1 mark for explaining each of three distinct methods (e.g., net mesh sizes, closed seasons, vessel limits, gear restrictions, marine reserves).
- (c)(i) [2 marks]: 1 mark for defined geographic marine area; 1 mark for restriction of destructive human activities/fishing.
- (c)(ii) [3 marks]: 1 mark for spillover effect (adult migration); 1 mark for larval dispersal; 1 mark for providing a nursery ground that maintains genetic diversity.
- (d)(i) [3 marks]: 1 mark for identifying difference (33); 1 mark for dividing by starting value (33/12); 1 mark for correct final calculation (275%).
- (d)(ii) [3 marks]: 1 mark for continued high fishing mortality; 1 mark for lack of habitat protection/refugia; 1 mark for competition or predation effects.
- (d)(iii) [3.6 marks]: 1 mark for loss of income/fishing grounds; 1 mark for increased operational/fuel costs of traveling further; 1.6 marks for overcrowding of non-protected areas and skepticism regarding short-term benefits.

Marking scheme

Marking scheme breakdown:
- (a)(i) 2 marks: Definition including 200 nautical miles (1) and sovereign resource rights (1).
- (a)(ii) 4 marks: Setting TACC (1), distribution of ITQs (1), legal catch limits (1), penalizing violations/incentivizing conservation (1).
- (b) 6 marks: Three named methods (3) paired with three accurate ecological explanations (3).
- (c)(i) 2 marks: Protected marine zone (1) where fishing/extraction is restricted/banned (1).
- (c)(ii) 3 marks: Spillover migration (1), larval dispersal by currents (1), nursery replenishment (1).
- (d)(i) 3 marks: Formula setup/working shown (1), correct numbers used (1), final answer of 275% (1).
- (d)(ii) 3 marks: High fishing pressure (1), habitat vulnerability (1), lack of resource protection (1).
- (d)(iii) 3.6 marks: Loss of revenue (1), increased travel/fuel costs (1), crowding in open zones/resistance to regulation (1.6).

Question 3 · Structured & Scenario Context

26.6 marks

### Context: Agriculture, Soil Erosion, and Sustainable Farming in New Zealand

New Zealand is a major global exporter of dairy products. However, the clearance of native forests on hilly terrain to create pasture has led to significant soil erosion and challenges with freshwater pollution.

**(a)(i)** State three causes of soil erosion on hilly pastures in New Zealand. [3]

**(a)(ii)** Describe the impacts of soil erosion on local freshwater river ecosystems. [4]

**(b)** Intensive dairy farming can lead to high levels of agricultural run-off containing nitrates and phosphates.

**(b)(i)** Describe the process of eutrophication in fresh water. [5]

**(b)(ii)** Explain how fencing off streams and planting riparian buffer zones (vegetated strips along riverbanks) can reduce eutrophication. [4]

**(c)** Outline three methods of sustainable agriculture, other than riparian zones, that farmers can use to maintain soil fertility and structure. [6]

**(d)** A farmer wants to estimate the soil organic matter content of two pastures:
* **Pasture A:** grazed by dairy cows for 20 years
* **Pasture B:** newly converted forest land

**(d)(i)** Describe a simple laboratory method to measure the percentage of organic matter in a dry soil sample. [3.6]

**(d)(ii)** Predict which pasture will have a higher soil organic matter content and explain your reasoning. [1]

Show answer & marking scheme

Worked solution

Detailed sub-question marking:
- (a)(i) [3 marks]: 1 mark for each valid cause of soil erosion (e.g., tree clearance, overgrazing, steep slopes, heavy rainfall, tillage on slopes).
- (a)(ii) [4 marks]: 1 mark for increased turbidity/blocked sunlight; 1 mark for gill clogging/macroinvertebrate damage; 1 mark for smothering of spawning gravels; 1 mark for nutrient enrichment causing ecosystem disruption.
- (b)(i) [5 marks]: 1 mark for nutrient runoff; 1 mark for algal blooms; 1 mark for death of deep-water plants due to light blockage; 1 mark for microbial decomposition of dead biomass; 1 mark for oxygen depletion (hypoxia) causing fish kills.
- (b)(ii) [4 marks]: 1 mark for fencing stopping direct manure/fecal deposits; 1 mark for reducing stream bank physical damage; 1 mark for riparian root uptake of soluble nutrients; 1 mark for physical trapping of suspended silt.
- (c) [6 marks]: 2 marks for each of three explained sustainable farming methods (e.g., crop rotation, cover crops, organic fertilizers, conservation tillage, contour plowing).
- (d)(i) [3.6 marks]: 1 mark for measuring starting dry soil mass; 1 mark for heating/burning off organic matter strongly; 1 mark for heating to constant mass; 0.6 marks for the calculation formula: \(\frac{\text{mass loss}}{\text{initial dry mass}} \times 100\).
- (d)(ii) [1 mark]: 0.5 marks for predicting Pasture B; 0.5 marks for explaining forest litter accumulation vs. pasture depletion.

Marking scheme

Marking scheme breakdown:
- (a)(i) 3 marks: Three causes of erosion on steep pastures (1+1+1).
- (a)(ii) 4 marks: High turbidity/light blockage (1), physical damage to fish gills (1), smothering of spawning habitats (1), introduction of nutrients (1).
- (b)(i) 5 marks: Excess nitrates/phosphates (1) -> Algal bloom (1) -> Light deprivation of plants (1) -> Bacterial decomposition (1) -> Severe oxygen depletion causing fish death (1).
- (b)(ii) 4 marks: Animal exclusion (stops feces/bank erosion) (1+1) and plant filter strips (absorbs dissolved nutrients/filters runoff sediment) (1+1).
- (c) 6 marks: Three named practices (3) with accurate descriptive explanations (3).
- (d)(i) 3.6 marks: Weight of dry sample (1), heat to burn organic matter (1), repeat to constant mass (1), calculate percentage loss (0.6).
- (d)(ii) 1 mark: Pasture B with reason (accumulation of forest biomass and lack of erosion depletion) (1).

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