2023 Cambridge IGCSE Environmental Management (0680) 模擬試題連答案詳解

To gain full marks, the response should clearly outline five distinct negative environmental impacts of open-cast mining: 1. Habitat destruction: removal of trees and vegetation destroys niches for animals, causing loss of local biodiversity. 2. Soil erosion: bare soil is easily washed away by heavy rainfall, leading to siltation of local waterways. 3. Acid mine drainage: water reacting with exposed minerals (like iron sulfides) creates highly acidic water that enters aquatic ecosystems, killing fish. 4. Air pollution: heavy machinery and blasting create dust that limits photosynthesis in nearby plants and causes respiratory issues in wildlife. 5. Noise and vibration: blasting disturbs local fauna, disrupting feeding and breeding patterns.

Award 1 mark for each valid environmental impact described, up to a maximum of 5 marks. Acceptable points include: Habitat destruction / loss of biodiversity; Soil erosion; Acid mine drainage / water pollution; Air pollution (dust / particulate matter); Noise / vibration pollution disrupting wildlife; Siltation of rivers; Visual pollution / scarring of the landscape. Reject: 'Economic cost' or 'effects on miners' health' as these are social/economic, not environmental impacts.

Sustainable marine harvesting requires restricting either when, where, how, or how much fishing occurs. 1. Quotas: Governments set Total Allowable Catches based on scientific population estimates to prevent overfishing. 2. Closed seasons: Restricting fishing during critical reproductive periods protects spawning adults. 3. Mesh size: Larger mesh holes allow juvenile fish to pass through, ensuring they survive to breeding age. 4. MPAs / No-take zones: Protecting key habitats allows fish stocks to recover and spill over into fishable areas. 5. Gear restriction: Banning non-selective or destructive gear (e.g. dynamite fishing, heavy bottom trawls) reduces bycatch and protects benthic ecosystems.

Award 1 mark for each clearly described management strategy up to a maximum of 5 marks. 1. Quotas / Total Allowable Catch (TAC); 2. Closed seasons; 3. Net mesh size restrictions / escape gaps; 4. Marine Protected Areas (MPAs) / reserves / no-take zones; 5. Restrictions on destructive fishing methods / gear types (e.g., banning bottom trawling, drift nets, or dynamite); 6. Licensing / limiting the number of fishing boats; 7. International agreements / patrol and monitoring. Credit description of how the method achieves sustainability.

Fertile soil consists of: 1. Mineral particles (approx. 45%): Sand, silt, and clay determine soil texture and provide mineral nutrients (like potassium, phosphorus, calcium) and physical anchorage. 2. Organic matter / humus (approx. 5%): Formed from decaying plant and animal remains; it increases water-holding capacity and binds soil particles together. 3. Water (approx. 25%): Essential for photosynthesis and serves as a medium to transport dissolved nutrients into root hairs. 4. Soil air (approx. 25%): Contains oxygen required for aerobic respiration in plant roots and soil microbes. 5. Soil living organisms: Bacteria, fungi, and earthworms break down organic matter into accessible nutrients and help mix and aerate the soil.

Award 1 mark for each correctly named component with its corresponding role, up to a maximum of 5 marks. 1. Mineral particles / sand, silt, clay -> Anchorage / source of plant nutrients. 2. Organic matter / humus -> Improves soil structure / retains moisture / releases nutrients upon decomposition. 3. Water -> Dissolves minerals / nutrient uptake / essential for photosynthesis. 4. Air / oxygen -> Root respiration. 5. Soil organisms / bacteria / earthworms -> Aeration / decomposition / nutrient cycling. Reject: general 'dirt' or 'rocks' without elaboration.

Generation process: 1. Hot water and/or steam is extracted from deep underground geothermal reservoirs. 2. The high-pressure steam is used to turn a turbine. 3. The rotating turbine drives an electrical generator to produce electricity. Sustainability advantages compared to coal (any two): 1. Renewable resource: Geothermal heat is constantly replenished by the Earth, unlike finite coal deposits which will eventually deplete. 2. Low carbon footprint: Geothermal power plants release negligible amounts of greenhouse gases (carbon dioxide) and sulfur dioxide compared to coal-fired power plants. 3. High reliability: Geothermal energy provides a constant baseline electricity supply, unlike fossil fuels which are burned up, and has a much smaller physical land footprint than coal mining operations.

Award up to 3 marks for the description of the generation process: 1 mark for extracting steam/hot water from underground; 1 mark for steam turning a turbine; 1 mark for turbine driving a generator. Award up to 2 marks for explaining two sustainability advantages: 1 mark for identifying it is renewable / will not deplete; 1 mark for low greenhouse gas emissions / no contribution to acid rain / minimal air pollution. Reject: 'It is free' or 'cheap' without environmental context.

(a) The nitrate concentration starts low at Location A (1.2 mg/L), spikes dramatically to a maximum of 14.8 mg/L at Location B (adjacent to the farm), and then gradually declines downstream through Location C (8.5 mg/L) to Location D (2.1 mg/L).

(b) The spike in nitrates at Location B triggers rapid growth of algae and aquatic plants (an algal bloom). As these plants and algae die off downstream, they are decomposed by aerobic bacteria. This decomposition process occurs heavily around Location C. Because the decomposers are aerobic, they consume vast amounts of dissolved oxygen during respiration, causing the oxygen concentration to plunge to 3.1 mg/L.

(c) Practices include: using organic fertilizers (like manure) instead of synthetic ones, establishing riparian buffer zones (vegetated strips) along waterways to absorb runoff, applying fertilizers only during dry periods to prevent wash-off, and practicing precision farming to apply only the exact amount of nutrient needed.

(d) Agroforestry involves planting trees alongside agricultural crops. The deep roots of the trees anchor the soil, preventing physical erosion. The tree canopy intercepts heavy rainfall, reducing water impact and surface runoff. Additionally, fallen leaves from the trees add organic matter back into the soil, improving its structure, water-retention capacity, and overall nutrient levels.

(a) Max 2 marks:
- 1 mark for identifying the sharp rise/peak at Location B (adjacent to the farm).
- 1 mark for identifying the gradual decline/decrease downstream towards Location D.

(b) Max 4 marks:
- 1 mark for explaining that high nitrates from B trigger rapid algae/plant growth (algal bloom).
- 1 mark for noting that these algae/plants eventually die.
- 1 mark for noting that aerobic bacteria decompose the dead organic matter.
- 1 mark for stating that these decomposers consume oxygen during respiration, leading to depletion.

(c) Max 2 marks:
- 1 mark for each valid practice (e.g., planting buffer zones/riparian strips, using cover crops, precise application timing, switching to organic fertilizer/compost).

(d) Max 3 marks:
- 1 mark for tree roots anchoring the soil particles.
- 1 mark for tree canopy reducing the physical impact of rain and slowing surface runoff.
- 1 mark for leaf litter decomposing to add organic matter and improve soil cohesion/nutrient content.

(a) Increase in wind generation = \(75 - 15 = 60\) TWh.
Percentage increase = \(\frac{60}{15} \times 100 = 400\%\).

(b) The country is transitioning away from coal, which saw a massive decline from 120 TWh to 45 TWh. Conversely, renewable energy sources have grown significantly, with wind increasing by 60 TWh and solar increasing by 35 TWh. Natural gas usage has risen slightly from 80 TWh to 95 TWh to meet growing overall energy demands (which rose from 220 TWh to 255 TWh).

(c) Advantages: Wind and solar are renewable and will not run out; they produce virtually zero greenhouse gas emissions during operation, helping to mitigate climate change.
Disadvantages: They are intermittent (weather-dependent), meaning they cannot guarantee continuous baseload power; they require massive land areas for wind farms and solar arrays compared to fossil fuel plants.

(d) Carbon capture and storage technology captures up to \(90\%\) of the carbon dioxide emissions produced from burning natural gas before it enters the atmosphere. The captured \(CO_2\) is then compressed and transported to be permanently stored deep underground, such as in depleted oil and gas reservoirs, preventing it from contributing to the greenhouse effect.

(a) Max 2 marks:
- 1 mark for correct working: \(\frac{75 - 15}{15} \times 100\) or equivalent.
- 1 mark for correct answer: \(400\%\).

(b) Max 3 marks:
- 1 mark for identifying the steep decline in coal generation.
- 1 mark for identifying the substantial growth in renewable energy sources (wind and/or solar).
- 1 mark for noting the slight increase in natural gas or the increase in total generation capacity.

(c) Max 4 marks:
- 2 marks for two valid advantages (e.g., reduction in air pollution, low running costs, reduction in greenhouse gases, resource conservation).
- 2 marks for two valid disadvantages (e.g., intermittency/unreliability, geographic limitations, high initial setup costs, grid integration challenges).

(d) Max 2 marks:
- 1 mark for describing the capture of carbon dioxide gas from power plant emissions.
- 1 mark for describing its permanent storage/sequestration underground (e.g., in geological formations).

(a) Sum of forest loss = \(120,000 + 85,000 + 50,000 + 35,000 + 15,000 = 305,000\) hectares.
Mean = \(\frac{305,000}{5} = 61,000\) hectares.

(b)
(i) Trees intercept rainfall with their leaves and branches, and their roots absorb water from the soil. Without trees, rainfall hits the ground directly, leading to rapid soil saturation and high surface runoff, which overfills local rivers and causes flooding.
(ii) Trees release water vapor into the atmosphere through the process of transpiration. When forests are cleared, transpiration rates decrease dramatically, meaning there is less moisture in the air to condense and form clouds, resulting in reduced rainfall.

(c) First, deforestation destroys critical habitats, leaving species without shelter. Second, it fragments populations, making it difficult for animals to find mates and maintain genetic diversity. Third, it removes primary producers, which disrupts local food webs and leads to the starvation of primary and secondary consumers.

(d) Ecotourism generates long-term income and employment for local people without destroying the ecosystem. It provides an economic incentive to keep the forests intact and protect wild animal species, unlike logging which provides only short-term profits and degrades resources permanently.

(a) Max 2 marks:
- 1 mark for correct working (summing the five values and dividing by 5).
- 1 mark for correct answer: \(61,000\) (accept with or without units, but reject if calculation is wrong).

(b) Max 4 marks:
- (i) 1 mark for identifying less interception/more surface runoff; 1 mark for explaining that this leads to rapid movement of water to rivers/flooding.
- (ii) 1 mark for identifying a reduction in transpiration; 1 mark for explaining that less water vapor in the air leads to fewer clouds and less precipitation.

(c) Max 3 marks:
- 1 mark for loss of habitats/shelter.
- 1 mark for disruption of food chains/webs due to loss of plant producers.
- 1 mark for habitat fragmentation isolating breeding groups.

(d) Max 2 marks:
- 1 mark for providing sustainable/long-term financial income/jobs to local people.
- 1 mark for preserving the forest/wildlife as an active economic asset (preventing destruction).

(a) Year 3, with a spawning biomass of 95,000 tonnes.

(b) 1. Quotas/Total Allowable Catches (TACs): Setting strict legal limits on the quantity of fish that can be caught allows a higher percentage of the adult population to survive and reproduce. 2. Closed seasons: Banning fishing during the key spawning months ensures breeding fish are not disturbed or caught before they can release their eggs. 3. Marine Protected Areas (MPAs): Establishing 'no-take' zones provides safe havens where fish can mature and reproduce undisturbed, with populations eventually spilling over into fishing zones.

(c) Target catch refers to the specific species and sizes of marine life that fishers intend to catch for commercial sale. Bycatch is the unwanted marine life (such as non-target fish, juvenile fish, turtles, or dolphins) caught unintentionally during the fishing process. Modified net designs can reduce this; for example, increasing the net mesh size allows small, juvenile fish to escape and grow to breeding age, while incorporating escape panels (such as Turtle Excluder Devices or TEDs) allows larger non-target animals to safely exit the net.

(a) Max 1 mark:
- 1 mark for identifying Year 3 and the value of 95,000 tonnes (or 95 thousands of tonnes).

(b) Max 6 marks:
- Award 1 mark for naming each valid strategy (up to 3 strategies).
- Award 1 mark for explaining how each named strategy helps fish stocks to recover.
- Examples of strategies: Quotas/TACs, closed seasons during spawning, Marine Protected Areas/No-take zones, minimum mesh size regulations, ban on destructive gear.

(c) Max 4 marks:
- 1 mark for defining 'target catch' (wanted commercial species).
- 1 mark for defining 'bycatch' (unwanted, non-target species caught accidentally).
- 1 mark for explaining how increased mesh size allows juvenile fish to escape.
- 1 mark for explaining how escape devices (like TEDs) allow larger non-target species to exit.

(a) The two main pathways are: 1) the atmosphere/air (via wind carrying particulate matter/dust), and 2) the hydrosphere/water (via surface runoff carrying dissolved heavy metals into local waterways).

(b) Mining operations have severely reduced soil quality: the soil pH has dropped significantly from a near-neutral 6.5 at the control site to a highly acidic 4.2 at the mine site, which can leach essential nutrients out of the soil. Additionally, runoff copper levels are extremely high (3.5 mg/L compared to 0.02 mg/L), indicating heavy metal toxicity in the surrounding substrate. This degradation of soil quality, coupled with direct land clearing, has decimated the local vegetation, reducing plant cover from \(85\%\) at the control site to just \(15\%\) at the mine site, as most plants cannot survive in toxic, acidic soils.

(c) Bioremediation (specifically phytoremediation) involves planting specialized, heavy-metal-tolerant plants (hyperaccumulators) in the contaminated soil. These plants absorb the toxic copper and other metals through their root systems and accumulate them in their leaves and stems. The plants are then harvested and safely incinerated or disposed of, thereby removing the toxins from the soil ecosystem.

(d) 1. Backfilling and contouring: The large open pits must be filled in with overburden (waste rock) and reshaped to resemble the natural topography. 2. Topsoil restoration: Stored topsoil must be spread back over the area to provide a fertile substrate. 3. Revegetation: Planting native trees, shrubs, and grasses to stabilize the soil, prevent erosion, and kickstart ecological succession.

(a) Max 2 marks:
- 1 mark for atmospheric pathway/air/dust/wind.
- 1 mark for aquatic pathway/water/surface runoff.

(b) Max 4 marks:
- 1 mark for stating that the soil has become highly acidic (pH dropped from 6.5 to 4.2).
- 1 mark for noting the massive increase in toxic copper concentration in water runoff (from 0.02 to 3.5 mg/L).
- 1 mark for noting the drastic reduction in vegetation cover (from 85% to 15%).
- 1 mark for linking the low vegetation cover directly to the acid/toxic soil conditions or direct clearing.

(c) Max 2 marks:
- 1 mark for identifying the use of specific plants/microbes to absorb or tolerate toxins (accept phytoremediation).
- 1 mark for explaining that these plants are harvested and removed, extracting the metals from the site.

(d) Max 3 marks:
- 1 mark for backfilling pits/reshaping the land to prevent hazards/landslides.
- 1 mark for adding/replacing topsoil to supply nutrients.
- 1 mark for replanting native/adapted vegetation to restore biodiversity and prevent soil erosion.

An effective evaluation should consider both the benefits of Marine Protected Areas (MPAs) and their limitations, while comparing them to alternative management strategies:

Arguments supporting MPAs as highly effective:
- They provide a complete safe haven where fish can feed, mature, and reproduce without human disturbance.
- They help restore benthic habitats damaged by destructive fishing methods like bottom trawling.
- The "spillover effect" means that as populations recover within the MPA, fish migrate into surrounding fishable waters, supporting the local fishing industry.

Why MPAs alone are not sufficient / other strategies are needed:
- MPAs do not protect highly migratory pelagic species (e.g., tuna) that travel long distances outside the boundaries.
- They are difficult and expensive to monitor and patrol, leading to illegal, unreported, and unregulated (IUU) fishing.
- Other strategies are needed to manage the wider ocean, such as:
- Quotas (Total Allowable Catches): limits the volume of fish harvested to sustainable levels (MSY).
- Closed seasons: prohibits fishing during critical spawning periods to allow replenishment.
- Net mesh size and shape regulations: allows juvenile fish to escape so they can reach breeding age.
- Restricting destructive gear: banning drift nets or pair trawling to reduce bycatch.
- Alternative livelihoods: supporting coastal communities to reduce overall fishing pressure.

Conclusion:
While MPAs are an essential tool for conservation, they are not the only effective way. A successful management strategy must combine MPAs with robust, internationally enforced regulations like quotas, gear restrictions, and closed seasons to ensure sustainable fisheries globally.

Level 3 (5-6 marks):
- Candidate presents a balanced evaluation of the statement.
- Demonstrates a clear understanding of both the strengths and limitations of MPAs.
- Discusses at least two other marine management strategies in detail (e.g., quotas, mesh size, closed seasons).
- Reaches a logical, supported conclusion based on the evidence presented.

Level 2 (3-4 marks):
- Candidate describes the role of MPAs but the evaluation is limited or one-sided.
- Mentions at least one other management strategy, but with less detail.
- The response has some structure but may lack a well-developed conclusion.

Level 1 (1-2 marks):
- Candidate makes simple points about MPAs or fishing rules.
- Little or no evaluation or comparison.
- Lacks a clear structure or conclusion.

[0 marks] - No response or response contains no relevant environmental management content.

(a) Runoff of synthetic nitrogen fertilizer carries nitrates/phosphates into the water. This causes rapid growth of algae (algal bloom) at the surface. The algae block sunlight from reaching aquatic plants below, which then die. Decomposers (aerobic bacteria) break down the dead plant matter, multiplying and consuming dissolved oxygen in the process, which suffocates fish and other clean-water organisms. (b) Standardization: 1. Use the exact same net size/mesh size at each site. 2. Kick the riverbed substrate for the same duration of time (e.g. 30 seconds). Safety: 1. Wear high-grip waterproof boots or waders to avoid slipping. 2. Wear thick gloves to handle debris and avoid cuts/infections. (c)(i) Total invertebrates at Site C = 12 (Mayflies) + 98 (Tubifex) = 110. Percentage of Mayflies = \((12 / 110) \times 100 = 10.91\%\) (accept 10.9% or 11%). (c)(ii) Mayfly abundance drops drastically from 84 at Site A to 3 at Site B. This is because Site B is right next to the agricultural runoff source where dissolved oxygen is depleted. Abundance then gradually increases downstream (12 at Site C, and 65 at Site D) as the fertilizer is diluted, and water aeration restores dissolved oxygen levels. (d) 1. Planting riparian buffer zones (strips of grass and trees along riverbanks) which filter and absorb nutrient runoff before it enters the water. 2. Using organic/slow-release fertilizers, which release nutrients gradually to match plant uptake, reducing excess nutrients left in the soil. (e)(i) \(1.0 \text{ m}^2 \times 10 \text{ quadrats} = 10 \text{ m}^2\) total sampled area. Mean biomass per \(1.0 \text{ m}^2 = 450 \text{ g} = 0.45 \text{ kg}\). 2 hectares = \(20,000 \text{ m}^2\). Total yield = \(0.45 \text{ kg} \times 20,000 = 9,000 \text{ kg}\). (e)(ii) Ten quadrats are not sufficient because they cover only \(10 \text{ m}^2\) out of \(20,000 \text{ m}^2\) (0.05% of the field), which is unrepresentative and susceptible to anomalies. Improvement: Increase the number of quadrats (e.g., to 50 or 100) or use a systematic grid layout.

(a) Max 3 marks: 1 mark for mentioning agricultural runoff containing nitrates/phosphates. 1 mark for algal bloom blocking light causing plants to die. 1 mark for bacterial decomposition depleting dissolved oxygen. (b) Max 4 marks: 1 mark each for two standardization points (e.g., same duration, same net size). 1 mark each for two safety precautions (e.g., protective clothing/footwear, checking water depth/flow). (c)(i) Max 2 marks: 1 mark for correct calculation of total (110) and division, 1 mark for correct final percentage (10.9% or 11%). (c)(ii) Max 3 marks: 1 mark for describing the decrease from A to B and increase downstream. 1 mark for relating low Mayfly numbers to low oxygen/pollution. 1 mark for relating downstream recovery to dilution/aeration. (d) Max 4 marks: 1 mark each for naming two valid practices. 1 mark each for explaining how they reduce runoff. (e)(i) Max 2 marks: 1 mark for showing correct working (converting grams to kg and multiplying by area). 1 mark for correct final answer of 9,000 kg. (e)(ii) Max 2 marks: 1 mark for explaining that the sample size is too small/unrepresentative. 1 mark for suggesting a valid improvement (increasing quadrat count).

(a) 1. Dig a small hole and place a plastic container so that the rim is exactly level/flush with the soil surface. 2. Place a flat cover (e.g., slate or wood) over the top, raised on small stones, to prevent rain filling the cup and predators eating caught insects. 3. Punch tiny drainage holes in the bottom of the cup to prevent drowning if water enters. 4. Check the traps at least once every 24 hours to ensure captured beetles are counted and released alive (ethical handling). (b)(i) All three zones have the exact same species richness (exactly 4 species: A, B, C, D). However, their species evenness is completely different. In Zone 2, Species B dominates with 85% of all individuals, indicating a highly disturbed, low-biodiversity community, whereas Zone 1 and Zone 3 show far more balanced distributions. Thus, richness alone does not reflect the ecological health or balance. (b)(ii) Total individuals in Zone 2 = 100, Species B = 85 (85%). Total individuals in Zone 3 = 100, Species B = 40 (40%). Difference = \(85\% - 40\% = 45\%\). (b)(iii) Zone 3, because the species abundances (30, 40, 15, 15) are closest to being equal/uniform. (c) Planting a monoculture of eucalyptus is a poor restoration strategy because it results in low structural and structural complexity, offers limited food sources, and may deplete groundwater. To support biodiversity, the team should: 1. Plant a diverse mixture of native tree species. 2. Include native understory vegetation (shrubs, grasses). 3. Create physical wildlife corridors to link the restored site to undisturbed areas. (d) 1. Lay out a long tape measure (the transect line) starting from the active mine edge and extending deep into the undisturbed forest. 2. Place quadrats at regular, fixed intervals (e.g., every 5 meters) along the tape. 3. Within each quadrat, identify all plant species present and estimate their percentage cover or count their abundance. 4. Record abiotic factors (like light intensity or soil compaction) at each interval. 5. Lay down multiple parallel transects (at least 3) in the same area to calculate mean values, which increases reliability and minimizes anomalies.

(a) Max 4 marks: 1 mark for placing trap flush with soil surface. 1 mark for adding a cover supported by stones. 1 mark for safety measures (drainage holes/no killing agent). 1 mark for checking frequently (ethical release). (b)(i) Max 3 marks: 1 mark for stating that species richness is identical (4 species) across all zones. 1 mark for using data (e.g., Zone 2 is dominated by Species B at 85%). 1 mark for concluding that richness fails to show the unevenness/imbalance of disturbed sites. (b)(ii) Max 2 marks: 1 mark for identifying the correct percentages (85% and 40%). 1 mark for calculating the difference of 45%. (b)(iii) Max 1 mark: Zone 3 with correct reasoning of balanced abundance. (c) Max 4 marks: 1 mark for evaluating the eucalyptus monoculture as poor/low-diversity. 1 mark each for three valid native planting recommendations. (d) Max 6 marks: 1 mark for laying a tape measure in a straight line. 1 mark for sampling at regular, fixed intervals. 1 mark for using quadrats. 1 mark for recording species identity and percentage cover/abundance. 1 mark for repeating multiple transects. 1 mark for keeping conditions standardized (same time of year, same equipment).

(a) 1. Weigh an empty crucible, then add a fresh soil sample and record the initial mass of the wet soil. 2. Place the crucible in a drying oven at \(105 \text{ }^{\circ}\text{C}\) overnight until all moisture evaporates, then re-weigh to determine the dry mass of the soil. 3. Heat the dry soil strongly over a Bunsen burner (or in a muffle furnace) for several minutes to fully burn off (combust) all organic matter. 4. Allow the crucible to cool, then weigh it. 5. Repeat the strong heating, cooling, and weighing process until a constant mass is reached. 6. Calculate the percentage of organic matter: \(\frac{\text{Dry Mass} - \text{Ignited Mass}}{\text{Dry Mass}} \times 100\). (b)(i) Moisture lost: Field X = \(120 \text{ g} - 90 \text{ g} = 30 \text{ g}\); Field Y = \(150 \text{ g} - 100 \text{ g} = 50 \text{ g}\). Percentage moisture: Field X = \(\frac{30}{120} \times 100 = 25\%\). Field Y = \(\frac{50}{150} \times 100 = 33.3\%\). (b)(ii) Organic matter lost: Field X = \(90 \text{ g} - 81 \text{ g} = 9 \text{ g}\); Field Y = \(100 \text{ g} - 88 \text{ g} = 12 \text{ g}\). Percentage organic matter: Field X = \(\frac{9}{90} \times 100 = 10\%\). Field Y = \(\frac{12}{100} \times 100 = 12\%\). (c)(i) Ploughing up and down the slope creates continuous vertical furrows that act as natural channels. During rainfall, water flows rapidly down these channels, gathering velocity and energy, which allows it to detach and carry away large volumes of fertile topsoil. (c)(ii) 1. Terracing: cutting flat steps into the slope to slow water flow. 2. Cover crops: planting fast-growing crops to keep soil covered and bound by roots during off-seasons. 3. Windbreaks: planting rows of trees/shrubs along fields to reduce wind velocity and wind-driven erosion. (d)(i) Mean pH = \(\frac{5.2 + 5.4 + 5.1 + 5.5 + 5.3}{5} = \frac{26.5}{5} = 5.3\). (d)(ii) An acidic pH reduces the availability of essential plant nutrients (like phosphorus and nitrogen) and increases the solubility of toxic metal ions (like aluminium) which damage root systems. The farmer can treat the soil by adding agricultural lime (calcium carbonate/calcium hydroxide) to neutralize the acidity and increase pH.

(a) Max 5 marks: 1 mark for drying soil at 105C to constant mass. 1 mark for recording dry mass. 1 mark for heating dry soil strongly to burn organic matter. 1 mark for repeating heating/cooling to constant mass. 1 mark for stating correct formula/calculation based on dry mass. (b)(i) Max 3 marks: 1 mark for showing correct formula/working for at least one field. 1 mark for Field X = 25%. 1 mark for Field Y = 33.3% (accept 33%). (b)(ii) Max 3 marks: 1 mark for showing correct formula/working based on dry mass (denominator must be dry mass: 90g and 100g). 1 mark for Field X = 10%. 1 mark for Field Y = 12%. (c)(i) Max 2 marks: 1 mark for stating furrows create channels. 1 mark for explaining that water gains speed/energy and washes soil down. (c)(ii) Max 3 marks: 1 mark each for three distinct erosion management techniques (e.g. terracing, windbreaks, cover crops, strip cropping). (d)(i) Max 1 mark: Correct calculation of 5.3. (d)(ii) Max 3 marks: 1 mark for noting reduced nutrient uptake. 1 mark for noting toxic metal release. 1 mark for adding lime/calcium carbonate to raise pH.

(a) Sources: 1. Blasting of rock using explosives. 2. Heavy machinery and haul trucks travelling on unpaved mine roads. 3. Mechanical crushing and grinding of ore. Impacts: 1. Deep lung penetration causing respiratory diseases like asthma, bronchitis, or silicosis. 2. Cardiovascular issues and reduced lung capacity. (b)(i) Independent variable: Distance downwind (m). Dependent variable: Mass of dust collected (mg). Trend: As distance downwind increases, the mass of dust collected decreases. The rate of decrease is rapid at first (from 450 mg to 120 mg between 100 m and 400 m) and then levels off, showing very little change between 500 m and 600 m. (b)(ii) Estimated mass: \(260 \text{ mg}\) (allow range of \(250 \text{ to } 270 \text{ mg}\)). Explanation: 250 m is the exact midpoint between the 200 m and 300 m sampling points. By interpolating the values (310 mg and 210 mg), the midpoint is calculated as: \(\frac{310 + 210}{2} = 260 \text{ mg}\). (c)(i) Rainfall falling on the exposed tailings piles leaches out toxic heavy metals (e.g., copper, lead, arsenic) and acidic minerals. This creates acid mine drainage which flows as surface runoff into the lake. The high acidity (low pH) damages fish gills, and the bioaccumulation of toxic heavy metals kills primary producers and invertebrates, leading to biomagnification up the food chain and collapse of the fishery. (c)(ii) 1. Build impermeable, lined tailings ponds to securely contain toxic slurry. 2. Construct diversion channels/bunds around the mine to redirect clean rainwater away from waste piles. (d) 1. Backfilling: filling the open pit with overburden (waste rock) or allowing it to safely fill with water to form a lake. 2. Land grading: reshaping the land surface to natural contours to prevent landslides and soil erosion. 3. Soil restoration: spreading the original topsoil (which was stored during initial excavation). 4. Revegetation: planting native grasses, shrubs, and trees to stabilize the soil and restore ecological habitats.

(a) Max 4 marks: 1 mark each for two valid mine-related dust sources. 1 mark each for two health impacts. (b)(i) Max 4 marks: 1 mark for independent variable (distance downwind). 1 mark for dependent variable (mass of dust). 2 marks for describing the trend (1 mark for general negative correlation, 1 mark for noting the rapid initial decline followed by leveling off). (b)(ii) Max 2 marks: 1 mark for giving an estimate between 250 mg and 270 mg. 1 mark for explaining interpolation between the 200 m (310 mg) and 300 m (210 mg) data points. (c)(i) Max 4 marks: 1 mark for leaching of heavy metals/acids from tailings. 1 mark for runoff entering the lake (acid mine drainage). 1 mark for low pH affecting aquatic life (gills/reproduction). 1 mark for bioaccumulation/biomagnification through the aquatic food web. (c)(ii) Max 2 marks: 1 mark each for two active management strategies (e.g., clay liners, retaining walls, bunds, water treatment). (d) Max 4 marks: 1 mark each for four sequential restoration steps (e.g., backfilling, grading, spreading topsoil, revegetation with native species).