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

Botkin & KellerEnvironmental Science 5e

Chapter 5

The Biogeochemical Cycles


How Chemicals Cycle

• Biogeochemical Cycle– The complete path a chemical takes through

the four major components – or reservoirs – of Earth’s systems1. Atmosphere

2. Hydrosphere

3. Lithosphere

4. Biosphere


Chemical Reactions

• Ch emical reaction:– The process in which new chemicals are

formed from elements and compounds through chemical change


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 phosphorusnitrogen 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


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


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


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


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


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


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


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


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.


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


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 Chapter 5 The Biogeochemical Cycles.

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