Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 56.4 Earth Is Changing Rapidly as a Result of Human Actions
Human activities are drastically altering Earth's ecosystems. This concept outlines four major environmental changes caused by humans—nutrient enrichment, toxin accumulation, climate change, and ozone depletion—and their cascading effects on biodiversity, ecosystem health, and global sustainability.
1. Nutrient Enrichment
- Humans redistribute nutrients via agriculture, waste, and industry
- Excess nitrogen and phosphorus exceed the critical load, causing:
- Groundwater contamination
- Eutrophication in lakes and coastal waters
- Example: Mississippi River → Gulf of Mexico dead zone
- Lake Erie: algal blooms + overfishing → fish extinction
2. Toxins in the Environment
- Thousands of synthetic chemicals are released into ecosystems
- Some toxins accumulate in fat tissues and biomagnify up food chains
- Examples:
- DDT: thins bird eggshells → population collapse
- PCBs: found 5,000× more concentrated in gull eggs than phytoplankton
- Pharmaceuticals: estrogens feminize fish, collapse populations
- Plastic waste:
- Large plastics = ingestion hazards
- Microplastics: widespread in aquatic systems and food webs
- Coral reefs with plastic → 20× more disease
3. Climate Change and Greenhouse Gases
- CO₂ levels have risen over 50% since the Industrial Revolution
- Greenhouse gases (CO₂, CH₄, H₂O) trap heat → global warming
- Earth has warmed ~1°C; 18 of 19 hottest years occurred since 2001
- Biological effects:
- Species shift ranges; some decline (e.g., bumblebees, pikas)
- Coral bleaching from marine heat waves
- Pine forests weakened → beetle outbreaks
- Arctic sea ice loss turns CO₂ sink into a source
- Models predict up to +3°C by 2100 without intervention
- Paris Agreement aims to limit warming, but needs strict enforcement
4. Ozone Depletion
- Stratospheric ozone absorbs UV; damaged by CFCs
- Ozone hole over Antarctica → seasonal UV spikes
- UV damages DNA, increases skin cancer, and harms phytoplankton
- Montreal Protocol (1987): phased out most CFCs
- Ozone layer is recovering, but illegal emissions raise concern
In a Nutshell
Human-driven changes—excess nutrients, synthetic toxins, greenhouse emissions, and ozone-depleting compounds—are reshaping Earth’s biosphere at unprecedented speed. While some solutions (e.g., banning CFCs) show success, reversing climate change and pollution will require global cooperation, technological innovation, and sustained ecological awareness.