📚Study Guide: Aquatic and Terrestrial Pollution
Unit 8: Aquatic and Terrestrial Pollution
Pollution of water and soil threatens human health, biodiversity, and ecosystem services worldwide. This unit examines the sources, types, and effects of pollutants in aquatic and terrestrial environments, as well as the methods used to treat wastewater and remediate contaminated sites. Water pollution categories include point sources (discrete locations like factory pipes and sewage outfalls) and nonpoint sources (diffuse runoff from agricultural fields, urban streets, and construction sites). Oxygen-demanding wastes (BOD), nutrients (nitrogen, phosphorus), pathogens (coliform bacteria), heavy metals (mercury, lead, cadmium), and synthetic organic compounds (pesticides, pharmaceuticals, plastics) all degrade water quality. Eutrophication occurs when excess nutrients trigger algal blooms; subsequent decomposition depletes dissolved oxygen, creating dead zones where aquatic life cannot survive. Solid waste management includes landfills (engineered burial), incineration (waste-to-energy), recycling, and composting. The AP exam frequently asks students to interpret dissolved oxygen profiles, explain biomagnification of persistent organic pollutants, and evaluate waste management strategies using the waste hierarchy (reduce, reuse, recycle). Hazardous waste--toxic, ignitable, corrosive, or reactive--requires special handling under regulations like RCRA and CERCLA (Superfund). Bioremediation and phytoremediation use living organisms to clean up contaminated soil and water.
Key Concepts
- Water Pollution Types: Point sources (industrial discharge, sewage treatment plants) are easier to regulate. Nonpoint sources (agricultural runoff, urban stormwater) are diffuse and harder to control. Major pollutants: pathogens, nutrients, sediments, heavy metals, synthetic organics, thermal pollution.
- Eutrophication: Excess N and P -> algal bloom -> algal death -> bacterial decomposition -> dissolved oxygen (DO) depletion -> fish kills and dead zones. The Gulf of Mexico dead zone at the mouth of the Mississippi River is a prominent example.
- BOD and DO: Biochemical oxygen demand (BOD) measures the oxygen required to decompose organic wastes. High BOD reduces dissolved oxygen (DO), stressing aquatic organisms. The oxygen sag curve shows DO declining downstream of a pollution source and recovering as decomposition completes.
- Biomagnification: Persistent organic pollutants (POPs) such as DDT, PCBs, and methylmercury accumulate in fatty tissues and increase in concentration at higher trophic levels. Top predators (eagles, tuna, polar bears) reach lethal concentrations.
- Solid Waste Management: Sanitary landfills use liners and leachate collection to prevent groundwater contamination. Incineration reduces volume by 90% but produces air pollutants and toxic ash. Recycling saves energy and raw materials but requires market demand. Composting diverts organic waste from landfills and produces soil amendment.
- Hazardous Waste: RCRA (cradle-to-grave tracking) and CERCLA (Superfund cleanup of abandoned sites). Treatment methods: physical (filtration), chemical (neutralization), biological (bioremediation), and thermal (incineration).
Vocabulary
- Dissolved Oxygen (DO): The amount of oxygen dissolved in water, essential for aquatic respiration; declines with increasing temperature and pollution.
- BOD (Biochemical Oxygen Demand): The amount of oxygen consumed by microorganisms during the decomposition of organic matter in water; a measure of organic pollution.
- Septic Tank: An underground container for treating household sewage in rural areas; solids settle and are digested by bacteria, while effluent drains into a leach field.
- Leachate: Liquid that drains from a landfill, containing dissolved and suspended contaminants; collected and treated to prevent groundwater pollution.
- Persistent Organic Pollutant (POP): A toxic chemical that resists degradation and accumulates in organisms (e.g., DDT, PCBs, dioxins).
- Phytoremediation: The use of plants to absorb, concentrate, or metabolize contaminants from soil or water.
Essential Formulas
- BOD = (DO_initial - DO_final) x dilution factor
- % Waste Diverted = (waste recycled + composted) / total waste generated x 100
Common Mistakes
- Confusing Eutrophication and Acidification: Eutrophication is nutrient enrichment -> algal blooms -> oxygen depletion. Acidification is pH decrease (usually from acid rain or CO2 absorption in oceans).
- Thinking Landfills Are Just Dumps: Modern sanitary landfills are engineered with clay/plastic liners, leachate collection systems, and methane capture. They are designed to minimize environmental impact.
- Confusing Bioaccumulation and Biomagnification: Bioaccumulation is the buildup of a substance in an individual organism over time. Biomagnification is the increase in concentration at successive trophic levels in a food web.
- Ignoring Nonpoint Sources: Nonpoint source pollution (agricultural runoff, urban stormwater) is the leading cause of water quality impairment in the US, not industrial point sources.
AP Exam Strategies
- Interpret Oxygen Sag Curves: Identify the pollution source, the zone of degradation (low DO), and the zone of recovery. Explain that self-purification occurs if the stream's assimilative capacity is not exceeded.
- Draw Food Webs for Biomagnification: Sketch a simple aquatic food chain (phytoplankton -> zooplankton -> small fish -> large fish -> eagle) and show increasing pollutant concentration at each level.
- Apply the Waste Hierarchy: Prioritize solutions: reduce > reuse > recycle > recover energy > dispose. Explain why source reduction is preferred over end-of-pipe treatment.
- Propose Remediation Strategies: For contaminated sites, match the pollutant to the appropriate technology: bioremediation for hydrocarbons, phytoremediation for metals, incineration for hazardous organics.
Real-World Applications
- Gulf of Mexico Dead Zone: Agricultural runoff from the Midwest delivers excess nitrogen and phosphorus down the Mississippi River, creating a summer dead zone averaging ~5,000 square miles.
- Great Pacific Garbage Patch: Ocean gyres concentrate floating plastics; microplastics enter the food web, threatening marine life and potentially human health.
- Love Canal and Superfund: The Love Canal disaster (toxic waste buried beneath a neighborhood) led to the creation of CERCLA (Superfund), authorizing federal cleanup of hazardous waste sites.