Population Dynamics Over Time
Trophic State
Eutrophication occurs when excess nutrients (nitrogen and phosphorus from agricultural runoff, sewage) fuel explosive algal growth. Dense blooms block sunlight, killing submerged vegetation. When algae die, bacterial decomposition consumes dissolved oxygen, creating hypoxic dead zones (<2 mg/L O₂). The Gulf of Mexico dead zone covers ~22,000 km² annually. Harmful algal blooms (HABs) by cyanobacteria produce toxins lethal to fish and mammals. Stratified, warm, calm water with high nutrients is the recipe for disaster — wind mixing can break stratification and delay collapse.