2024 AP AP Environmental Science Practice Paper with Answers

(a) Riparian zones provide regulating services such as stream temperature moderation (via canopy shade), bank stabilization, and flood mitigation, as well as supporting services like wildlife migration corridors and nesting habitat.

(b) The root systems of riparian vegetation bind soil particles to prevent bank erosion, while dense aboveground vegetation slows surface water runoff, causing suspended sediment particles to drop out of suspension before entering the aquatic system.

(c) Common nutrients in synthetic fertilizers include nitrates (\(\text{NO}_3^-\)) / ammonium (\(\text{NH}_4^+\)) or phosphates (\(\text{PO}_4^{3-}\)).

(d) Excess limiting nutrients cause rapid proliferation of algae (algal bloom). When the algae die, heterotrophic aerobic decomposers (bacteria) decompose the biomass. The cellular respiration of these decomposers consumes available dissolved oxygen, lowering oxygen concentrations to hypoxic or anoxic levels.

(e) A testable hypothesis expresses a clear relationship between the variables, e.g.: An increase in the width of the forested riparian buffer will lead to a significant decrease in stream nitrate concentration following storm events.

(f) The independent variable is the width of the riparian buffer (0 m, 10 m, or 30 m).

(g) The dependent variable is the concentration of dissolved nitrate in the stream water (in \(\text{mg/L}\)).

(h) Reach 1 (0 m buffer) functions as the control group, establishing a baseline of ambient nutrient runoff in the absence of any buffer treatment for comparison with the experimental reaches.

(i) Compaction compresses soil particles together, decreasing macropore space and permeability. Consequently, water cannot infiltrate the ground quickly, leading to increased surface runoff volume.

(j) Feasible sustainable agricultural practices include:
- Planting winter cover crops to uptake residual nutrients.
- Practicing precision fertilizer application or soil testing to avoid over-application.
- Using no-till/conservation tillage methods to maintain soil structure.
- Applying slow-release organic fertilizers.

### 10 Points Total (1 point per part)

(a) 1 point
Accept one of the following:
- Bank stabilization / prevention of riverbank collapse.
- Providing habitat / nesting sites / migration corridors for wildlife.
- Shading the waterway / moderating stream water temperature.
- Mitigating flooding / regulating flood water storage.
- Carbon sequestration by riparian trees.
Do NOT accept water filtration / pollutant trapping (excluded by prompt).

(b) 1 point
Accept one of the following:
- Roots bind and anchor the soil particles, preventing soil detachment/erosion.
- Stems/vegetation physically slow overland runoff, promoting sedimentation/settling of particulates before water reaches the stream.

(c) 1 point
Accept one of the following:
- Nitrate / Nitrogen (\(\text{NO}_3^-\), \(\text{NH}_4^+\))
- Phosphate / Phosphorus (\(\text{PO}_4^{3-}\))

(d) 1 point
Response must include BOTH the algal bloom/death AND the decomposer/bacterial consumption of dissolved oxygen:
- High nutrients cause an algal bloom, and when algae die, aerobic decomposers/bacteria break down the biomass, consuming dissolved oxygen (DO) and causing hypoxia/anoxia.

(e) 1 point
Accept a valid testable directional or null hypothesis relating buffer width to nitrate concentration:
- Increasing riparian buffer width will decrease stream nitrate concentrations.
- Wider riparian buffers will result in lower nitrate runoff than narrower buffers.
- Buffer width will have no effect on stream nitrate concentrations.

(f) 1 point
Accept one of the following:
- Width of the riparian buffer / buffer zone
- Riparian buffer strip treatment (0 m, 10 m, 30 m)

(g) 1 point
Accept one of the following:
- Concentration of dissolved nitrate / nitrate levels in stream water
- Amount of nitrate (in \(\text{mg/L}\))

(h) 1 point
Accept one of the following:
- Reach 1 serves as an experimental control / baseline.
- It allows researchers to compare stream reaches with buffers to an unbuffered reach.

(i) 1 point
Accept one of the following:
- Compaction decreases soil pore space/porosity/permeability, reducing water infiltration into the ground and increasing surface runoff.
- Compressed soil cannot absorb rainwater efficiently, so more water flows overland carrying nutrients.

(j) 1 point
Accept one of the following:
- Planting cover crops to absorb excess nutrients during off-seasons.
- Implementing precision agriculture / targeted variable-rate fertilizer application.
- Using drip irrigation to reduce surface runoff.
- Practicing crop rotation with legumes to reduce synthetic fertilizer application.
- Practicing no-till or conservation tillage farming.
- Contour plowing / terracing to slow water flow down slopes.

(a) Between 2000 and 2010, aquaculture production increased by \(60 - 32 = 28\text{ million metric tons}\), which is the greatest increase of any decade shown (1980–1990: +10, 1990–2000: +17, 2010–2020: +25).

(b) Wild fishery capture rose from 65 million metric tons in 1980 to 86 million metric tons in 2000, after which it plateaued/leveled off at approximately 89–90 million metric tons through 2020.

(c) Overharvesting leads to population collapses of commercially targeted fish species, loss of marine biodiversity, food web disruptions (e.g., fishing down marine food webs), or significant bycatch mortality of non-target marine animals (e.g., sea turtles, dolphins, seabirds).

(d) The hypothesis is refuted. Although aquaculture grew rapidly, wild fishery capture remained near its peak (around 90 million metric tons) rather than declining. Furthermore, many aquaculture operations rely on wild-caught forage fish to produce fishmeal and fish oil, maintaining or increasing fishing pressure on lower trophic levels.

(e) Mangroves provide shoreline stabilization and storm surge attenuation, buffering coastal communities against hurricanes and erosion. Alternatively, they serve as major blue carbon sinks (sequestering carbon in sediments) or act as natural biofilters filtering sediment and runoff from land.

(f) Aquaculture effluent contains high concentrations of unconsumed feed and metabolic wastes rich in nitrogen and phosphorus, which leads to cultural eutrophication, resulting in algal blooms, reduced dissolved oxygen (hypoxia), and fish kills in surrounding waters.

(g) Due to the 10% rule of ecological efficiency (energy loss via respiration and heat at each trophic step), it requires multiple kilograms of wild forage fish at a lower trophic level to produce one kilogram of a farmed carnivorous species at a higher trophic level, wasting substantial trophic energy.

(h) Seaweeds are photosynthetic autotrophs that take up dissolved inorganic nutrients (nitrogen, phosphorus, ammonium) excreted by the finfish, thereby reducing nutrient loads and preventing eutrophication and hypoxia.

(i) Implementing enforceable catch quotas / Individual Transferable Quotas (ITQs), establishing Marine Protected Areas (MPAs) / no-take marine reserves, setting seasonal fishing bans during spawning periods, or mandating modified gear (e.g., turtle excluder devices or larger mesh sizes).

(j) For Marine Protected Areas: Provides permanent habitat protection for benthic ecosystems (such as biogenic coral reefs) and non-target endangered organisms. For ITQs: Enhances safety at sea, stabilizes market prices, and guarantees long-term economic livelihoods for fishers without overcapitalization.

Part (a): 1 point
- Award 1 point for identifying 2000–2010 (or 2000 to 2010).

Part (b): 1 point
- Award 1 point for describing that wild fishery capture increased initially (from 1980 to 2000) and then leveled off/plateaued/stabilized from 2000 to 2020.

Part (c): 1 point
Accept one of the following:
- Collapse/depletion of target fish populations/stocks below sustainable replacement levels.
- Bycatch and accidental mortality of non-target species (e.g., sea turtles, cetaceans, nontarget fish).
- Disruption of marine food webs/trophic cascades (e.g., fishing down marine food webs).
- Habitat degradation from destructive fishing gear (e.g., bottom trawling).

Part (d): 1 point
- Award 1 point for stating that the hypothesis is refuted AND explaining that wild capture rates have remained high/plateaued (not decreased) OR explaining that aquaculture often uses wild-caught fish (forage fish/fishmeal) to feed farmed species.

Part (e): 1 point
Accept one of the following (service other than fish habitat):
- Coastal protection/buffering against storm surges/hurricanes/tsunamis.
- Shoreline stabilization / prevention of coastal erosion.
- Carbon sequestration / carbon sink (blue carbon storage).
- Natural filtration of sediments and terrestrial runoff.
- Ecotourism / recreational opportunities.

Part (f): 1 point
Accept one of the following:
- Eutrophication/algal blooms caused by excess nitrogen/phosphorus from uneaten feed and feces.
- Hypoxia / decreased dissolved oxygen (DO) levels due to microbial decomposition of organic waste.
- Introduction of chemical pollutants such as antibiotics/pesticides/disinfectants into coastal waterways.
- Increased turbidity/sedimentation reducing sunlight penetration for benthic plants.

Part (g): 1 point
- Award 1 point for explaining that energy is lost as metabolic heat between trophic levels (the 10% rule / thermodynamic inefficiency), meaning multiple kilograms of wild forage fish biomass are required to generate one kilogram of farmed carnivorous fish biomass.

Part (h): 1 point
- Award 1 point for describing that seaweeds act as primary producers that absorb/take up excess dissolved inorganic nutrients (nitrogen/phosphorus/ammonia) excreted by fish, mitigating nutrient pollution/eutrophication/algal blooms.

Part (i): 1 point
Accept one of the following:
- Establishing Marine Protected Areas (MPAs) / no-take marine reserves.
- Implementing Individual Transferable Quotas (ITQs) / total allowable catch limits.
- Regulating fishing gear (e.g., larger mesh nets, circle hooks, bans on bottom trawling, requiring Turtle Excluder Devices).
- Instituting seasonal fishing closures / moratoria during breeding/spawning seasons.
- Eliminating government fuel/vessel subsidies that promote overcapacity.

Part (j): 1 point
- Award 1 point for a valid ecological or economic justification connected to the specific solution proposed in part (i) (other than maintaining target population size):
- If MPAs proposed: Preserves non-target benthic biodiversity / enhances ecotourism revenues / protects critical non-fish marine organisms (e.g., coral reefs, marine mammals).
- If ITQs proposed: Improves economic stability/income predictability for fishermen / reduces hazardous derby-style fishing during storms.
- If gear restrictions proposed: Reduces bycatch mortality of endangered non-target species / decreases physical damage to benthic seafloor habitats.

(a) Methane (\(\text{CH}_4\))

(b) Containing manure prevents heavy runoff of excess nitrogen and phosphorus during storm events. This reduces the risk of cultural eutrophication, preventing harmful algal blooms, severe dissolved oxygen depletion, and aquatic dead zones.

(c) The government could offer low-interest loans, capital cost grant subsidies, tax rebates, or guarantee favorable feed-in tariffs (net metering) for electricity sold back to the regional electric grid.

(d) The policy lowers upfront capital costs for the farmer, provides a diversified stream of farm income from selling excess electricity back to the grid, or produces high-quality digested solids that can be sold or reused as pathogen-free bedding and rich organic fertilizer.

(e) Daily biogas production:
\[ 4{,}000\text{ cows} \times 55\text{ kg manure/cow/day} \times 0.04\text{ m}^3\text{ biogas/kg manure} = 8{,}800\text{ m}^3\text{ biogas/day} \]

(f) Annual electricity production:
\[ 8{,}800\text{ m}^3/\text{day} \times 365\text{ days/year} = 3{,}212{,}000\text{ m}^3\text{ biogas/year} \]
\[ 3{,}212{,}000\text{ m}^3/\text{year} \times 2.2\text{ kWh}/\text{m}^3 = 7{,}066{,}400\text{ kWh/year} \text{ (or } 7.07 \times 10^6\text{ kWh/year)} \]

(g) Net \(\text{CO}_2\) reduction:
\[ \text{Net reduction per kWh} = 0.95\text{ kg CO}_2/\text{kWh} - 0.05\text{ kg CO}_2/\text{kWh} = 0.90\text{ kg CO}_2/\text{kWh} \]
\[ 7{,}066{,}400\text{ kWh} \times 0.90\text{ kg CO}_2/\text{kWh} = 6{,}359{,}760\text{ kg CO}_2 \text{ (or } 6.36 \times 10^6\text{ kg CO}_2) \]

Question 3 Marking Breakdown (10 points total):

(a) [1 point]
Accept one of the following:
- Methane / CH4

(b) [1 point]
Accept one of the following:
- Decreased runoff of nitrogen/phosphorus, reducing algal blooms / eutrophication / hypoxic conditions.
- Reduced contamination of waterways by fecal coliform bacteria / pathogens.
- Prevention of catastrophic spills/overflows associated with unlined open lagoons during flood events.

(c) [1 point]
Accept one of the following:
- Offering government grants, tax rebates, or low-interest subsidies for equipment purchase.
- Establishing net-metering / feed-in tariff policies to allow farmers to sell generated electricity at guaranteed rates.
- Creating a carbon credit / offset market where farmers earn revenue for captured methane.

(d) [1 point]
Accept one of the following consistent with part (c):
- Reduces farm operating/utility costs.
- Generates secondary revenue streams from selling surplus power or digested solids as soil amendments.
- Eliminates noxious odors for surrounding residential communities.

(e) [2 points]
- 1 point for correct setup:
Accept: 4,000 × 55 × 0.04 (or 220,000 × 0.04)
- 1 point for correct calculation:
Accept: 8,800 m^3 (or 8.8 × 10^3 m^3)

(f) [2 points]
- 1 point for correct setup:
Accept: 8,800 × 365 × 2.2 (or 3,212,000 × 2.2)
- 1 point for correct calculation:
Accept: 7,066,400 kWh (or 7.07 × 10^6 kWh, 7.066 × 10^6 kWh)

(g) [2 points]
- 1 point for correct setup:
Accept: (0.95 - 0.05) × 7,066,400 (or 0.90 × 7,066,400, or 6,713,080 - 353,320)
- 1 point for correct calculation with units:
Accept: 6,359,760 kg CO2 (or 6.36 × 10^6 kg, 6.4 × 10^6 kg)