Chapter 5

1. Chapter 5 The Biogeochemical Cycles Botkin & Keller Environmental Science 5e

2. How Chemicals Cycle • Biogeochemical Cycle • The complete path a chemical takes through the four major components – or reservoirs – of Earth’s systems • Atmosphere • Hydrosphere • Lithosphere • Biosphere Botkin & Keller Environmental Science 5e

3. Chemical Reactions • Ch emical reaction: • The process in which new chemicals are formed from elements and compounds through chemical change Botkin & Keller Environmental Science 5e

4. Biogeochemical Cycles and Life:Limiting Factors • Macronutrients • Elements required in large amounts by all life • Include the “big six” elements that form the fundamental building blocks of life: carbon oxygen hydrogen phosphorus nitrogen sulfur • Micronutrients • Elements required either in • small amounts by all life or • moderate amounts by some forms of life and not all by others • Limiting factor • When chemical elements are not available at the right times, in the right amounts, and in the right concentrations relative to each other Botkin & Keller Environmental Science 5e

5. The Geologic Cycle • The Geologic Cycle: • The processes responsible for formation and change of Earth materials • Best described as a group of cycles: • Tectonic • Hydrologic • Rock • Biochemical Botkin & Keller Environmental Science 5e

6. Tectonic Cycle • Tectonic cycle: • Involves creation and destruction of the solid outer layer of Earth, the lithosphere • Plate tectonics: • The slow movement of these large segments of Earth’s outermost rock shell • Boundaries between plates are geologically active areas Botkin & Keller Environmental Science 5e

7. Tectonic Cycle: Plate Boundaries • Divergent plate boundary: • Occurs at a spreading ocean ridge, where plates are moving away from one another • New lithosphere is produced (seafloor spreading) • Convergent plate boundary • Occurs when plates collide • Produces linear coastal mountain ranges or continental mountain ranges • Transform fault boundary • Occurs where one plate slides past another • San Andreas Fault in California Botkin & Keller Environmental Science 5e

8. The Hydrologic Cycle • The Hydrologic Cycle: • The transfer of water from the oceans to the atmosphere to the land and back to the oceans. Includes: • Evaporation of water from the oceans • Precipitation on land • Evaporation from land • Runoff from streams, rivers, and sub-surface groundwater Botkin & Keller Environmental Science 5e

9. The Rock Cycle • The rock cycle: • Numerous processes that produce rocks and soils • Depends on other cycles: • tectonic cycle for energy • Hydrologic cycle for water • Rock is classified as • Igneous • Sedimentary • Metamorphic Botkin & Keller Environmental Science 5e

10. The Carbon Cycle • Carbon is the element that anchors all organic substances • The carbon cycle: • Carbon combines with and is chemically and biologically linked with the cycles of oxygen and hydrogen that form the major compounds of life Botkin & Keller Environmental Science 5e

11. Fig 5.15 Botkin & Keller Environmental Science 5e © 2005 John Wiley and Sons Publishers

12. The Carbon Cycle:Unanswered Issues • The Missing Carbon Sink • Substantial amounts of carbon dioxide released into the atmosphere but apparently not reabsorbed and thus remaining unaccounted for Botkin & Keller Environmental Science 5e

13. The Carbon-Silicate Cycle • The carbon-silicate cycle: • A complex biogeochemical cycle over time scales as long as one-half billion years. • Includes major geological processes, such as: • Weathering • Transport by ground and surface waters • Erosion • Deposition of crustal rocks • Believed to provide important negative feedback mechanisms that control the temperature of the atmosphere. Botkin & Keller Environmental Science 5e

14. The Nitrogen Cycle • The nitrogen cycle: • Cycle responsible for moving important nitrogen components through the biosphere and other Earth systems • Extremely important because nitrogen is required by all living things • Nitrogen fixation: • The process of converting inorganic, molecular nitrogen in the atmosphere to ammonia or nitrate • Denitrification: • The process of releasing fixed nitrogen back to molecular nitrogen Botkin & Keller Environmental Science 5e

15. The Phosphorus Cycle • The phosphorus cycle: • Involves the movement of phosphorus throughout the biosphere and lithosphere • Important because phosphorus is an essential element for life and often is a limiting nutrient for plant growth. Botkin & Keller Environmental Science 5e