Inside This Unit: The Full Breakdown
Aquatic and Terrestrial Pollution covers the sources, effects, and remediation of pollution in water and soil. This unit examines point and nonpoint source pollution, eutrophication, bioaccumulation, solid waste, and hazardous waste management.
Why it matters
Water and soil pollution questions are common on the AP Environmental Science exam. You must identify pollution sources, explain how pollutants move through ecosystems (bioaccumulation, biomagnification), and evaluate treatment and prevention strategies.
Key concepts
- Point source pollution comes from a single identifiable source (factory pipe, sewage outfall). Nonpoint source pollution comes from diffuse sources (agricultural runoff, urban stormwater).
- Eutrophication occurs when excess nutrients (nitrogen, phosphorus) cause algal blooms that deplete oxygen when they decompose, creating dead zones.
- Bioaccumulation is the buildup of toxins in an individual organism over time. Biomagnification is the increasing concentration of toxins at higher trophic levels.
- Solid waste management strategies follow the hierarchy: reduce, reuse, recycle, then landfill or incineration.
Water Pollution
Water pollution threatens both human health and aquatic ecosystems. Point sources (factory discharges, wastewater treatment plant outfalls) are regulated by permits and relatively easy to monitor. Nonpoint sources (agricultural runoff carrying fertilizers and pesticides, urban stormwater carrying oil and heavy metals, sediment from construction sites) are harder to control and are now the leading cause of water quality problems. Pathogens from untreated sewage cause waterborne diseases. Thermal pollution from power plant cooling water raises water temperature, reducing dissolved oxygen. Mercury, lead, and other heavy metals are persistent pollutants that do not break down. The Clean Water Act regulates point source discharges in the U.S. and has significantly improved water quality since its passage in 1972, though nonpoint source pollution remains a major challenge.
Eutrophication and Bioaccumulation
Eutrophication is the enrichment of water bodies with excess nutrients, primarily nitrogen and phosphorus from agricultural fertilizers, animal waste, and sewage. The process follows a predictable sequence: nutrient input stimulates rapid algal growth (algal bloom), the dense algae block sunlight to submerged plants, the algae die and decompose, decomposition by bacteria consumes dissolved oxygen, creating hypoxic (low-oxygen) or anoxic (no-oxygen) dead zones that kill fish and other aquatic organisms. The Gulf of Mexico dead zone, fed by Mississippi River agricultural runoff, is one of the largest in the world. Bioaccumulation occurs when organisms absorb toxins faster than they can eliminate them, building up concentrations over a lifetime. Biomagnification occurs when toxin concentrations increase at each trophic level, as predators consume many contaminated prey organisms. DDT and mercury are classic examples of biomagnifying pollutants.
Solid and Hazardous Waste
Solid waste management is a growing challenge as consumption increases globally. Sanitary landfills are the most common disposal method: waste is compacted, covered daily, and the site is lined with clay and plastic to prevent leachate (contaminated water) from reaching groundwater. Landfills produce methane from anaerobic decomposition, which can be captured for energy. Incineration reduces waste volume by about 90% and can generate electricity, but produces air pollutants and toxic ash. The waste hierarchy prioritizes source reduction (producing less waste), reuse, recycling, and composting before disposal. Hazardous waste (toxic, corrosive, flammable, or reactive materials) requires special handling. The Superfund program (CERCLA) identifies and cleans up contaminated hazardous waste sites in the U.S. E-waste (electronic waste) is a rapidly growing category containing heavy metals and toxic materials.
AP exam tip
When answering AP questions about pollution, always distinguish between point and nonpoint sources, because the control strategies are fundamentally different. Also, clearly differentiate bioaccumulation (within one organism over time) from biomagnification (increasing concentration up the food chain).
Connections to other units
- Unit 1 (Ecosystems): Pollution disrupts energy flow and nutrient cycling in both aquatic and terrestrial ecosystems.
- Unit 5 (Land and Water Use): Agricultural practices and urbanization are major sources of both water and soil pollution.
- Unit 2 (Biodiversity): Pollution is one of the HIPPCO threats to biodiversity, reducing species diversity in affected habitats.
