Biogeochemical Cycles: Carbon, Nitrogen, Phosphorus, and Hydrologic Cycle (Lecture Notes)

Question-and-answer flashcards covering definitions, reservoirs, processes, and key concepts of the Carbon, Nitrogen, Phosphorus, and Hydrologic cycles as described in the notes.

What is the Carbon Cycle?

The movement of atoms and molecules containing carbon between sources (reservoirs) and sinks in ecosystems; a biogeochemical cycle that helps regulate matter flow and can be influenced by human activity.

What is a reservoir (sink) in the carbon cycle?

A place that stores carbon, such as the atmosphere, plant biomass, surface ocean, sediments, or fossilized carbon.

What does the term biogeochemical cycle mean in the context of carbon cycling?

A self-regulating movement of chemical molecules through living (biotic) and non-living (abiotic) components of ecosystems.

Where is atmospheric carbon primarily stored and in what form?

In the atmosphere as carbon dioxide (CO2); a short-term reservoir.

Which process converts CO2 into glucose during photosynthesis?

Photosynthesis.

Which process returns CO2 to the atmosphere during metabolism?

Cellular respiration.

What is air-sea gas exchange?

A process at the ocean surface that transfers CO2 between the atmosphere and the surface ocean, linking terrestrial and aquatic carbon exchange.

What are major carbon reservoirs besides the atmosphere and surface ocean?

Terrestrial biomass (plants and animals), surface ocean biomass, sediments, and fossilized carbon.

What is sedimentation in the carbon cycle?

The accumulation of carbon in sediments, forming a reservoir over time.

What is fossilized carbon and why is it important?

Ancient plant and animal carbon stored as coal, oil, or natural gas; a long-term carbon reservoir.

How do human activities affect the carbon cycle?

Extraction and combustion of fossil fuels release CO2 into the atmosphere, disrupting carbon balance.

Where is carbon stored that has not been transformed into CO2 through metabolism?

In the bodies of producers and consumers (terrestrial) and in organisms at the ocean surface (aquatic).

What characterizes fast carbon cycling?

Rapid movement of carbon through the biosphere driven by metabolism, especially photosynthesis and respiration; the atmosphere is the primary reservoir with short residence times.

What role does decomposition play in the carbon cycle?

Decomposer organisms break down dead matter, returning carbon to the air as CO2 and enabling transfer to soil and ocean sediments.

What is lithification and its relevance to the carbon cycle?

The process by which sediments become rock (e.g., limestone) under time and pressure, representing a long-term carbon reservoir.

What happens when fossil fuels are combusted?

Carbon stored as fossilized carbon is released as CO2 into the atmosphere, increasing atmospheric carbon.

Where are the long-term carbon reservoirs located?

Deep ocean sediments and fossil carbon (coal, oil, natural gas).

What is the Nitrogen Cycle?

The movement of nitrogen between sources and sinks through fixation, ammonification, nitrification, assimilation, and denitrification; a biochemical cycle influenced by human activity.

Why is nitrogen important to life?

Nitrogen is a major component of amino acids and nucleic acids; essential for organisms and often a limiting factor for growth.

What are the five key steps of the nitrogen cycle listed in the notes?

Nitrogen fixation, ammonification, nitrification, assimilation, and denitrification.

What is nitrogen fixation?

Conversion of atmospheric N2 into ammonia (NH3) or ammonium (NH4+) by lightning or soil/root microbes.

What is ammonification?

Conversion of organic nitrogen to ammonia (NH3) or ammonium (NH4+) by soil bacteria and decay processes.

What is nitrification and its two stages?

Oxidation of ammonium (NH4+) to nitrite (NO2−) and then to nitrate (NO3−), which plants uptake most readily.

What is assimilation in the nitrogen cycle?

Uptake of nitrate (NO3−) by plant roots and transfer through the food web.

What is denitrification?

Conversion of nitrate (NO3−) to nitrogen gas (N2) by soil bacteria, returning nitrogen to the atmosphere.

Which reservoir contains most atmospheric nitrogen and in what proportion?

The atmosphere; about 78% of nitrogen is in the air.

Why is nitrogen often a limiting factor in ecosystems?

Because its availability limits producer growth; fertilizers can add nitrogen to boost growth.

Give examples of organisms that need nitrogen to grow.

Plants, trees, algae, phytoplankton, and grasses (producers) and organisms up the food chain.

What is the Phosphorus Cycle?

The movement of phosphorus between terrestrial and aquatic sources and sinks; no atmospheric phase; one of the four biochemical cycles.

Why is phosphorus considered a limiting factor in ecosystems?

Phosphorus cycles slowly and is often scarce; producers need it to grow, and fertilizers provide phosphorus.

What are the major reservoirs of phosphorus?

Sediments and rocks containing phosphate; weathering releases phosphate into soils and waters.

How does phosphorus move from soil to aquatic systems?

Phosphorus is dissolved from soils into lakes/streams, taken up by producers, or carried by runoff into aquatic systems.

What is assimilation in the phosphorus cycle?

Uptake of phosphorus by marine/aqueous organisms and incorporation into biological molecules; some phosphate remains dissolved, enabling sedimentation.

What is lithification in the phosphorus cycle?

Ocean sediments form rocks through lithification; phosphorus re-enters the cycle as rocks weather or uplifted.

What is the Hydrologic Cycle?

The movement of water through solid, liquid, and gaseous phases between sources and sinks; a biogeochemical cycle driven primarily by the sun; oceans are the major reservoir.

What drives the hydrologic cycle?

The sun provides energy that drives evaporation and other phase changes of water.

What are the major reservoirs in the hydrologic cycle?

Oceans as the primary reservoir; freshwater sources include ice caps, groundwater, rivers, lakes, wetlands.

What are the main steps of hydrologic cycling?

Evaporation/evapotranspiration/sublimation, atmospheric transport and precipitation, collection in ice/snow/rivers/lakes/oceans, surface runoff, infiltration/seepage, groundwater recharge and storage, cycle restarts.