Unit 8 Pollution Processes in Food Webs and Waters: Nutrients, Oxygen, and Persistent Toxins

Eutrophication

Enrichment of a water body with nutrients (especially nitrogen and phosphorus) that stimulates excessive algal/aquatic plant growth and often leads to oxygen depletion.

Algal bloom

Rapid increase in algae or phytoplankton; often a visible symptom of eutrophication rather than the underlying nutrient-driven process itself.

Natural eutrophication

Slow, long-term nutrient and sediment accumulation as lakes age, gradually increasing productivity over time.

Cultural eutrophication

Human-accelerated nutrient loading (e.g., fertilizer, sewage) that speeds up eutrophication far beyond natural rates.

Dissolved oxygen (DO)

Oxygen gas dissolved in water; essential for aquatic organisms and often reduced during eutrophication.

Hypoxia

Low dissolved oxygen condition that can stress or kill aquatic organisms and contribute to “dead zones.”

Anoxia

Complete absence of dissolved oxygen in water, often causing severe die-offs of aerobic aquatic life.

Limiting nutrient

The nutrient in shortest supply relative to demand; adding it causes the greatest increase in primary production (often P in freshwater, N in many marine/coastal systems).

Point source pollution

Pollution from a single, identifiable discharge location (e.g., wastewater treatment plant outfall, industrial pipe).

Nonpoint source pollution

Diffuse pollution carried by runoff from broad areas (e.g., farms, lawns, streets) rather than a single pipe.

Turbidity

Cloudiness of water caused by suspended particles or dense plankton; reduces light penetration and can harm submerged vegetation.

Aerobic decomposition

Breakdown of organic matter by microorganisms using oxygen; can sharply reduce DO after algal blooms die and sink.

Dead zone

Area of water (often bottom waters) with persistent hypoxia/anoxia where many organisms cannot survive.

Stratification

Layering of water by temperature/density (warm, less dense surface over cooler, denser bottom) that reduces mixing and limits oxygen delivery to deeper water.

Internal loading

Release of nutrients (especially phosphorus) from sediments back into the water under low-oxygen conditions, reinforcing future blooms.

Riparian buffer

Vegetated strip along waterways that slows runoff, promotes infiltration, and traps sediments and nutrients before they enter streams/lakes.

Wetlands (nutrient filtering)

Ecosystems that can reduce nutrient pollution by removing nitrate biologically and storing some phosphorus in sediments.

Stormwater management

Practices (e.g., rain gardens, permeable pavement, retention basins) that reduce runoff from impervious surfaces and limit nutrient transport to waterways.

Tertiary (advanced) wastewater treatment

Additional wastewater treatment steps designed to remove nutrients like nitrogen and phosphorus beyond primary/secondary treatment.

Bioaccumulation

Buildup of a chemical in an individual organism over time when uptake exceeds elimination.

Biomagnification

Increase in pollutant concentration at successively higher trophic levels because predators consume many contaminated prey and the chemical is retained in tissues.

Persistent pollutant

Chemical that resists breakdown (sunlight, chemical reactions, or metabolism), allowing it to remain in the environment and organisms for long periods.

Lipophilic (fat-soluble) pollutant

Chemical that dissolves in fats/oils more than water, tends to be stored in fatty tissues, and is hard for organisms to excrete.

Methylmercury

A toxic form of mercury produced by microbes in aquatic systems that readily accumulates in tissues and biomagnifies in food webs.

DDT (eggshell thinning)

Persistent insecticide known for biomagnifying in food chains; high concentrations in birds of prey caused eggshell thinning and reduced reproduction.