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

2. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
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. Environmental Science 5e
Fig 5.15
Idealized diagram illustrating photosynthesis for a green plan (tree) and generalized reaction.
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
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. Environmental Science 5e
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. Environmental Science 5e
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