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Across
  1. 4. Underground rock layer that stores water
  2. 6. Nutrient buildup in water causing algal blooms
  3. 7. Harmful compounds that destroy the ozone layer
  4. 8. First species to colonize bare land
  5. 10. Organisms interacting with each other and their environment
  6. 13. A group of organisms of the same species in one area
  7. 14. Non-living components of an ecosystem
  8. 18. Index used to estimate population size
  9. 19. Long-term weather patterns of an area
  10. 20. All populations living together in an area
Down
  1. 1. Planting trees again in an area where forests were removed
  2. 2. Growing one crop over a large area
  3. 3. The variety of species in an ecosystem
  4. 5. Gradual change in ecosystems over time
  5. 9. Layer of atmosphere that blocks UV radiation
  6. 11. Using resources without harming future generations
  7. 12. Relationship between dependents and working-age population
  8. 15. Fuels made from biological material
  9. 16. Living components of an ecosystem
  10. 17. Thick polluted air caused by sunlight reacting with pollutants