Element

Reservoir Stage

Where the element is found outside of the biosphere

Uptake Process

How the element gets into living matter

Release Process(es)

How the element is released from living matter

Alternate Forms/Processes

Other environmentally significant forms or processes involving the element

Carbon

Carbon dioxide (CO₂) in the atmosphere

Photosynthesis

Respiration, Combustion

Fossil fuels

Dissolved CO₂ (carbonate)

Shells of mollusks, etc.

Carbonate minerals (eg, limestone)

Nitrogen

Nitrogen gas in the atmosphere (N₂)

Nitrogen fixation: The conversion of N₂ to ammonia (NH₄+)

Nitrification: The conversion of NH₄⁺ to nitrate (NO₃^-)

NH₄⁺ and NO₃^- are taken up by plants and incorporated into proteins

Death and excretion release organic nitrogen to the ecosystem

Decay converts organic nitrogen to ammonia

Denitrification converts nitrate to nitrogen

Water pollution: nitrogen from sewage and fertilizers causes overgrowth of algae, depleting Long Island Sound of oxygen

Air pollution: smog contains numerous nitrogen compounds including nitric acid (HNO₃)

Chemical fertilizer: humans use fossil fuel energy to fix nitrogen industrially

Phosphorus

Phosphate rock

Leaching by water

Uptake by plants

Excretion, death and decay

Detergents (now uncommon)

Chemical fertilizer

Water pollution: runoff from farmland contaminates Lake Champlain and the Chesapeake Bay

Oxygen

Oxygen gas (O₂)

Water (H₂O)

Carbon dioxide (CO₂)

Photosynthesis: oxygen in CO₂ is incorporated into carbohydrates while oxygen from H₂O is released as O₂

Respiration: oxygen in O₂ is breathed in and promptly released in CO₂ and H₂O

Oxide minerals (ice, iron oxide, other metals)

Ozone (O₃) is both vitally important in the stratosphere and an air pollutant close to the ground

Environments that contain oxygen are called aerobic; environments without oxygen are called anaerobic or anoxic

The presence or absence of oxygen dramatically affects the chemical state of all other substances