AP Environmental Science Unit 5 Notes: Resource Extraction, Land/Water Use, and Sustainability

Impacts of Overfishing

What overfishing is (and what it is not)

Overfishing happens when fish and other aquatic organisms are harvested faster than their populations can replace themselves through reproduction and growth. The key idea is rate: a fishery can take a large number of fish in one year and still be sustainable if the population is healthy and replenishes quickly, but even a smaller catch can be unsustainable if the species reproduces slowly or if the ecosystem is stressed.

A common misconception is that overfishing only means “a species goes extinct.” In AP Environmental Science, you’re usually thinking in terms of population decline, fishery collapse (catch drops dramatically because the population can’t support harvest), and ecosystem-level changes—long before extinction.

Why overfishing matters in environmental science

Overfishing is a resource extraction problem with wide ripple effects:

• Food systems and livelihoods: Many communities rely on fisheries for protein and income. When a fishery collapses, the social and economic impacts can be immediate.
• Biodiversity and ecosystem stability: Removing large numbers of organisms—especially top predators—can restructure entire food webs.
• Equity and governance: Fisheries are often shared resources. When regulation is weak, the situation resembles the tragedy of the commons: individuals benefit from taking more, while the long-term costs are distributed across everyone.

How overfishing damages populations and ecosystems

Overfishing causes harm through several connected mechanisms.

1) Removing breeding adults reduces future population growth

Many fisheries target the largest individuals because they’re most profitable. But large, older fish are often the most successful breeders. When you disproportionately remove them, you reduce reproduction and shrink the population’s ability to rebound.

• Slow-growing, late-maturing species (many sharks, some deep-sea fish) are especially vulnerable.
• Even when a species can reproduce quickly, intense harvest can push it below a level where reproduction is efficient.

2) Bycatch wastes life and disrupts food webs

Bycatch is the unintentional capture of non-target species (such as sea turtles, dolphins, juvenile fish, or seabirds) in fishing gear.

• Bycatch can reduce populations of already vulnerable species.
• Catching juveniles of the target species is also a problem—if fish are taken before they reproduce, population recovery becomes much harder.

3) Trophic cascades: removing predators reshapes the ecosystem

If a fishery removes a top predator (or a key mid-level predator), the prey species can increase, which may reduce organisms lower in the food chain. This is a trophic cascade.

Example mechanism:

• Overharvest a predatory fish.
• Its prey (smaller fish or invertebrates) increases.
• Those prey consume more zooplankton or algae-grazers.
• Algae may increase, changing water quality and habitat.

On exams, you’re often expected to explain this as a chain of cause-and-effect, not just state “the ecosystem changes.”

4) Habitat damage from certain fishing methods

Some fishing techniques physically damage habitat.

• Bottom trawling (dragging heavy nets along the seafloor) can destroy benthic habitats, including areas that function like “nurseries” for juvenile fish.
• Habitat damage reduces the ecosystem’s capacity to support fish populations—even if harvest later decreases.

5) “Fishing down the food web” changes what humans harvest

When large, desirable species decline, fishing pressure often shifts to smaller species lower on the food chain. This can keep total catch numbers looking stable for a while even as the ecosystem becomes simplified and less resilient.

Overfishing in action: realistic scenarios you might analyze

Scenario A: A fishery’s catch stays high, then suddenly crashes

This pattern can happen because high-efficiency technology (large fleets, sonar, longlines, factory ships) can maintain high catches even while the population is declining. Eventually the population becomes too small to support the industry, and catch drops.

What AP-style answers look for:

• You connect technology + open access + delayed feedback to collapse.

Scenario B: A protected area increases fish populations nearby

Marine protected areas (MPAs) restrict fishing in certain zones. Over time, populations inside can grow, and some adult fish and larvae move out of the protected area (often called “spillover”), supporting nearby fisheries.

What AP-style answers look for:

• You explain the mechanism: protection increases survival and reproduction, which increases biomass and replenishment.

Common management strategies (how humans try to prevent overfishing)

Overfishing is not inevitable—management can align harvest with long-term sustainability.

• Catch limits / quotas: A cap on total allowable catch. Works best when enforcement is strong and the quota is science-based.
• Size limits: Protect juveniles (and sometimes very large breeders) so individuals can reproduce.
• Seasonal closures: Avoid harvesting during spawning periods.
• Gear restrictions: Reduce bycatch (for example, turtle excluder devices in some shrimp fisheries) or reduce habitat damage.
• Individual transferable quotas (ITQs): Allocate shares of the total allowable catch to individuals/companies. This can reduce the “race to fish,” but it raises equity questions about who gets the rights.
• Aquaculture (fish farming): Can reduce pressure on wild fish, but can also create pollution, habitat conversion, and disease/parasite spread if poorly managed.

A frequent misconception: “Aquaculture is always sustainable.” In reality, sustainability depends on species, feed sources, waste management, and siting (for example, whether coastal habitat like mangroves is cleared).

Exam Focus

• Typical question patterns:
  • Explain two ecological impacts of overfishing, often requiring a cause-and-effect chain (population decline, trophic cascade, bycatch).
  • Compare two management strategies (for example, quotas vs. MPAs) and evaluate benefits/limitations.
  • Interpret a scenario where fishing pressure changes species composition or leads to collapse.
• Common mistakes:
  • Treating overfishing as only an “extinction” issue instead of a population and ecosystem issue.
  • Forgetting bycatch and habitat damage as distinct impacts (not just “fewer fish”).
  • Proposing a solution (like aquaculture) without acknowledging tradeoffs (pollution, disease, feed inputs).

Impacts of Mining

What mining is

Mining is the extraction of geologic resources—such as metals (copper, iron, gold), nonmetal minerals (phosphate), and fossil fuels (coal)—from Earth. In Unit 5, you focus on mining as a land-use practice that reshapes landscapes, generates pollution, and can create long-term waste management challenges.

A helpful way to think about mining: you are moving and processing huge amounts of rock to concentrate a relatively small amount of desired material. That concentration step is where many environmental impacts originate.

Why mining matters

Mining supports modern life (construction materials, electronics, energy), but it often produces significant environmental externalities:

• Land disturbance and habitat loss from clearing vegetation, building roads, and removing overburden.
• Water pollution from chemicals and acid-producing reactions.
• Air pollution and greenhouse gases from machinery and processing.
• Waste (tailings, slag) that can persist and require monitoring.

A common misconception is that “reclamation fixes the problem.” Reclamation can reduce hazards and restore some ecosystem function, but it may not fully replace original habitat complexity, soil structure, or water quality.

Types of mining and how they disturb land

Mining methods differ, but all involve tradeoffs between access, cost, worker safety, and environmental impact.

How mining causes water pollution

1) Acid mine drainage (AMD)

Acid mine drainage occurs when sulfide minerals exposed by mining react with oxygen and water to form sulfuric acid. The acidic water can then dissolve (mobilize) toxic metals.

Why this matters:

• Lower pH harms aquatic organisms.
• Dissolved metals (like iron, copper, aluminum, or others depending on geology) can be toxic and can contaminate drinking water sources.
• AMD can continue long after a mine closes because exposed materials remain reactive.

A common student error is to describe AMD as “acid spilled from machines.” It’s usually a chemical reaction created by exposing certain rocks to air and water.

2) Sediment and erosion

Removing vegetation and disturbing soil increases erosion. Sediment runoff into streams can:

• Smother fish eggs and benthic habitats
• Reduce light penetration, lowering photosynthesis in aquatic plants
• Carry attached pollutants (some contaminants bind to particles)

3) Leaching and processing chemicals

Some mining operations use chemical solutions to separate desired metals from ore. If these solutions leak or are improperly stored, they can contaminate groundwater and surface water.

Tailings, slag, and long-term waste

Tailings are the crushed rock and leftover materials after the desired resource is extracted. Tailings are often stored in piles or behind dams.

Key idea: tailings are not “just dirt.” They may contain:

• Residual chemicals used in processing
• Sulfide minerals that can create AMD
• Fine particles that can travel easily in wind and water

Tailings dam failures can release large volumes of contaminated slurry into waterways. Even without failures, long-term seepage is a concern.

Air pollution and climate impacts

Mining and processing can produce:

• Particulate matter from blasting, hauling, and crushing rock
• Sulfur dioxide and other emissions from smelting (processing metal ores)
• Greenhouse gas emissions from heavy machinery and energy use

In APES terms, you should connect these emissions to human health (respiratory issues) and broader atmospheric impacts.

Land impacts: fragmentation, subsidence, and biodiversity

Mining infrastructure (roads, pipelines, worker housing) can fragment habitat, making it harder for organisms to migrate, find mates, and maintain genetic diversity.

With subsurface mining, you can also see subsidence—the ground sinking when tunnels collapse or structural support is removed. Subsidence can damage buildings and alter drainage patterns.

Mitigation: what “better mining” looks like

Mining always has impacts, but policies and technologies can reduce harm.

• Reclamation: reshaping land, replacing topsoil, replanting vegetation. Works best when planned before mining begins.
• Water treatment: neutralizing acidity and removing metals from drainage.
• Liners and monitoring for tailings storage; careful dam engineering.
• Reducing demand through recycling: using recycled metals reduces the need for new extraction and can save energy.

A frequent misconception is that recycling is only about waste. In resource extraction, recycling is also a mining reduction strategy.

Exam Focus

• Typical question patterns:
  • Identify environmental impacts of a specific mining type (often surface vs. subsurface) and explain mechanisms (erosion, AMD, tailings).
  • Propose mitigation strategies and explain how they reduce a named impact.
  • Analyze a land-use scenario map or description for habitat fragmentation and water quality changes.
• Common mistakes:
  • Confusing tailings with “the extracted mineral” rather than the leftover waste.
  • Treating acid mine drainage as an equipment leak instead of a geochemical process.
  • Listing impacts without explaining a mechanism (for example, saying “water pollution” without describing sediment, acidity, or metals).

Impacts of Urbanization

What urbanization is

Urbanization is the growth of cities and the increasing proportion of people living in urban areas. In AP Environmental Science, urbanization is a land-use change that concentrates people, housing, roads, and industry—changing how water moves, how heat is stored, and how ecosystems function.

It’s easy to assume urbanization is only a “population” topic. It’s also a land and water use topic because cities transform land cover and create continuous demand for resources (energy, water, building materials) that come from outside the city.

Why urbanization matters

Urbanization can create efficiencies (shared infrastructure, smaller living spaces, public transit), but it also creates environmental challenges:

• Stormwater runoff and flooding due to impervious surfaces
• Water pollution from combined sewer overflows, oil/metal residues, and nutrient inputs
• Urban heat island effect raising temperatures
• Habitat loss and fragmentation
• Increased resource extraction elsewhere (mining for construction materials, water withdrawals, energy production)

A helpful connection: urbanization often increases demand for extracted resources (metals, sand/gravel, fossil fuels) and can indirectly intensify mining and overfishing through consumption.

How cities change the water cycle

1) Impervious surfaces increase runoff

Impervious surfaces (roads, parking lots, rooftops) prevent water from infiltrating into soil.

Mechanism:

• Rain falls.
• Instead of soaking into the ground, it runs quickly into storm drains and streams.
• Peak stream flow increases, raising flood risk.

Consequences:

• Less groundwater recharge (which can reduce base flow in streams during dry periods)
• More stream bank erosion because water arrives in faster, larger pulses

A common misconception is that “runoff is only a problem during heavy storms.” Even moderate rain can cause polluted runoff if large areas are impervious.

2) Runoff carries pollutants

Urban runoff often contains:

• Oil and grease from roads
• Heavy metals from vehicle wear and industrial sources
• Nutrients from lawns and landscaping
• Trash and microplastics

When these pollutants enter waterways, they can harm aquatic organisms and degrade drinking water sources.

3) Wastewater and sewage challenges

Cities generate large volumes of wastewater. Treatment plants reduce pathogens and nutrients, but problems can occur when:

• Infrastructure is outdated or overwhelmed.
• Storm events cause combined sewer overflows (in systems where stormwater and sewage share pipes), releasing untreated or partially treated waste.

This is often tested as a cause-and-effect chain: increased precipitation event plus combined system leads to overflow and water quality impacts (pathogens, low dissolved oxygen from decomposition, nutrient pollution).

Urban heat island effect

The urban heat island effect is when cities are warmer than surrounding rural areas.

Why it happens:

• Dark surfaces (asphalt, roofs) absorb more solar energy.
• Less vegetation means less cooling by evapotranspiration.
• Waste heat from vehicles, buildings, and industry adds warmth.

Why it matters:

• Higher energy demand for cooling can increase power plant emissions.
• Heat can worsen air quality by influencing atmospheric chemistry that contributes to smog.
• Heat waves become more dangerous for human health.

Mitigation examples:

• Planting trees and expanding green spaces
• Cool roofs and reflective pavement
• Green roofs (which also absorb rainfall)

Urban sprawl and land-use patterns

Urban sprawl is low-density development spreading outward from city centers.

Environmental impacts:

• Converts farmland, forests, and wetlands to development.
• Increases vehicle miles traveled, raising emissions.
• Fragments habitat into smaller patches, reducing biodiversity.

A nuanced point: dense urban living can reduce per-capita land use and transportation emissions, but only if infrastructure (public transit, walkability, mixed-use zoning) supports it.

Solid waste and consumption

Urban areas concentrate consumption and therefore waste:

• More packaging and single-use products increases landfill demand.
• Improperly managed waste contributes to litter and marine debris.

This connects back to resource extraction: reducing waste through reuse and recycling lowers demand for raw materials (mining, logging) and can reduce pollution.

Urbanization in action: examples you might see

Example A: A new shopping center increases flooding downstream

If a watershed gains large parking lots and rooftops, runoff rises. Streams respond with higher peak flows, erosion, and increased flood frequency.

A strong AP response explains:

• Impervious surface increases runoff
• Runoff increases peak discharge
• Higher discharge increases erosion and flooding

Example B: A city adds riparian buffers and green infrastructure

Green infrastructure (rain gardens, permeable pavement, bioswales) is designed to slow, store, and infiltrate stormwater.

What it changes:

• Reduces runoff volume and peak flow
• Filters pollutants through soil and plants
• Improves groundwater recharge

Exam Focus

• Typical question patterns:
  • Explain how impervious surfaces affect runoff, flooding, groundwater recharge, and water quality.
  • Identify and justify solutions (green infrastructure, zoning, public transit, riparian buffers).
  • Compare urban sprawl vs. smart growth in terms of environmental impacts.
• Common mistakes:
  • Saying “cities cause water pollution” without specifying a pathway (runoff, sewage overflow, industrial discharge).
  • Confusing groundwater recharge with surface runoff (they move in opposite directions when impervious cover increases).
  • Treating the urban heat island as “global warming” rather than a local land-cover and energy-balance effect.

Introduction to Sustainability

What sustainability means in AP Environmental Science

Sustainability is the ability to meet current human needs without compromising the ability of future generations to meet their needs. In AP Environmental Science, sustainability is less about a slogan and more about a decision-making framework: you evaluate whether a system can continue over time without depleting natural capital or causing unacceptable environmental damage.

Two key related terms:

• Natural capital: Earth’s resources and ecosystem services (soil, water, biodiversity, fossil fuels, forests).
• Ecosystem services: benefits humans receive from ecosystems, such as water filtration, pollination, climate regulation, and flood control.

A common misconception is that “sustainable” means “no impact.” Real sustainability usually means reduced impact within ecological limits, plus fair and feasible social systems.

Why sustainability belongs in resource extraction

Resource extraction (fishing, mining, forestry, water withdrawals) is where humans directly interact with natural capital. If extraction exceeds renewal rates (for renewables) or ignores pollution and waste (for nonrenewables), you get depletion and long-term costs.

• Overfishing is an example of failing to keep harvest within a population’s ability to replenish.
• Mining is an example where the resource is generally nonrenewable on human timescales, so sustainability emphasizes efficient use, recycling, and minimizing environmental harm.
• Urbanization affects sustainability by driving demand for extracted resources and altering land and water systems.

Renewable vs. nonrenewable resources (and the sustainability goal for each)

Renewable resources (like fish populations, forests, and freshwater in many contexts) can regenerate if managed within limits.

Nonrenewable resources (like most mineral ores and fossil fuels) form far too slowly to replace extraction on human timescales.

Sustainability goals differ:

• For renewables: keep use at or below regeneration and protect the ecosystem processes that support renewal.
• For nonrenewables: extend availability through conservation, efficiency, reuse, recycling, substitution, and reducing environmental damage from extraction.

Sustainable yield and the idea of limits

A central sustainability concept in APES is sustainable yield: the amount of a renewable resource that can be harvested without reducing the resource’s long-term availability.

How it works conceptually:

• A population grows through births and declines through deaths.
• If harvest is less than or equal to the population’s net growth over time, the population can remain stable.
• If harvest consistently exceeds net growth, the population declines.

This is why overfishing is often framed as exceeding sustainable yield.

Tragedy of the commons and governance solutions

The tragedy of the commons describes how individuals can overuse a shared resource when each person benefits from taking more but the costs of depletion are shared by everyone.

Fisheries are a classic example because:

• The ocean is hard to patrol.
• Benefits of catching more fish go to the fisher.
• Costs (population decline) are spread across all fishers and future years.

Sustainability responses usually involve changing incentives and rules:

• Clear access rights (who can fish where)
• Science-based limits (quotas)
• Monitoring and enforcement
• Community-based management or co-management

A common mistake is to assume “people are greedy” is the explanation. APES expects the structural explanation: incentives + lack of regulation + shared access.

Thinking in systems: life cycle impacts and externalities

Sustainability requires you to look beyond the immediate action.

• Life cycle thinking asks: What are the impacts of a product from extraction to manufacturing to use to disposal?
  • Example: a smartphone involves mining metals, energy-intensive manufacturing, and e-waste.
• Externalities are costs not included in the market price.
  • Example: the price of coal electricity might not include health costs from air pollution or ecosystem damage from mining.

When externalities exist, markets alone often overproduce environmentally harmful goods—so sustainability often involves policy tools.

Tools for moving toward sustainability (especially relevant to Unit 5)

1) Reduce, reuse, recycle (as extraction reduction)

These are sometimes taught as waste strategies, but in Unit 5 they also directly reduce extraction pressure.

• Recycling metals reduces the need for new mining and often reduces energy use compared with processing ore.
• Reuse and repair reduce demand for raw materials.

2) Environmental policy and planning

Approaches you might see in AP questions:

• Protected areas (MPAs, habitat conservation plans)
• Land-use planning (smart growth, zoning to reduce sprawl)
• Regulations on pollution discharge and mine reclamation requirements

3) Green infrastructure and ecosystem-based solutions

Working with natural processes can improve sustainability:

• Wetlands and riparian buffers filter water and reduce flooding.
• Urban tree canopy reduces heat and improves air quality.

Sustainability “in action” across the three impact topics

• Overfishing: sustainable catch limits, bycatch reduction, and protected areas aim to keep harvest within ecological limits.
• Mining: sustainability emphasizes minimizing land and water impacts, safe waste storage, and reducing demand through recycling and efficiency.
• Urbanization: sustainability focuses on designing cities to use land and water efficiently (green infrastructure, public transit, compact development) while reducing pollution.

Exam Focus

• Typical question patterns:
  • Define sustainability-related terms (sustainability, natural capital, ecosystem services) and apply them to a scenario (fishing, mining, urban development).
  • Explain how a policy tool (quota, MPA, reclamation, green infrastructure) supports sustainability and what tradeoffs remain.
  • Identify an example of the tragedy of the commons and propose a governance solution.
• Common mistakes:
  • Defining sustainability as “no resource use” rather than use within ecological limits and with long-term planning.
  • Treating renewable resources as automatically sustainable even when extraction exceeds regeneration.
  • Proposing solutions without connecting them to a mechanism (for example, saying “use green infrastructure” without explaining runoff reduction and filtration).