8 The Phosphorus Cycle Practice Flashcards

A set of 70 vocabulary flashcards covering the phosphorus cycle, its chemical properties, biological importance, soil dynamics, and global reserves.

Phosphorus

A highly reactive element found in Column 15 of the periodic table, present in the Earth's crust at approximately $0.1\%$ mass.

Column 15 Elements

A group of non-metals on the periodic table including nitrogen, phosphorus, arsenic, antimony, and bismuth.

Free elemental form

The state in which phosphorus is NOT found in the Earth's crust due to its high reactivity; instead, it exists as insoluble minerals.

Guano

A traditional agricultural source of phosphorus derived from bird droppings, extensively quarried in tropical countries.

Bone ash

An agricultural source of phosphorus primarily composed of calcium phosphate, created by burning the residue of carcasses.

Phosphate ($PO_4^{3-}$)

The most prevalent compound of phosphorus and its derivatives, featuring a negative three charge.

Biological applications of Phosphorus

Essential for life as it forms cell walls, is a key component of DNA and RNA, and is critical for adenosine pools ($ATP$, $ADP$, and $AMP$).

Industrial applications of Phosphorus

Used as essential fertilizer, fire retardant, food additive, metallurgical synthesis component, water softener, and in matches.

Organophosphate molecules

Phosphorus-based building blocks used in products ranging from pesticides to chemical warfare agents.

Phospholipids

Phosphate sugars essential to the structure of cell walls.

Phosphorus Cycle simplicity

By comparison to the carbon and nitrogen cycles, the phosphorus cycle is described as much simpler.

Weathering and Erosion

The process by which phosphate-associated minerals are released from the lithosphere into water reservoirs.

Assimilation

The process by which plants and animals (from archaea to mammals) take up phosphorus for essential life functions.

Lithosphere

The Earth's outer shell where phosphate is stored in sedimentary rocks through tectonic and mineralization activities.

Deep sea sediment

The environment where phosphorus eventually settles after migrating through soil and marine habitats, becoming part of the lithosphere over millions of years.

Blue color coding (Soil Diagram)

In the lecture notes, this represents inputs of phosphorus into the soil.

Red color coding (Soil Diagram)

In the lecture notes, this represents the loss of phosphorus from the soil.

Green pools (Soil Diagram)

In the lecture notes, these represent the components into which phosphorus will sequester within the soil.

Primary minerals

A soil phosphorus pool where phosphate is bound up within a mineral form.

Mineral surfaces

Soil locations, such as clay, sesquioxides (iron and aluminium), or carbonaceous forms, where phosphate will sequester.

Sesquioxides

Oxides of iron and aluminium that serve as surfaces for phosphorus sequestration in the soil.

Secondary compounds

Amorphous, non-mineral materials such as phosphorus bound with calcium, iron, manganese, and aluminium.

Soil solution phosphorus

The central, key pool of inorganic phosphorus derivatives ($PO_4^{3-}$) that plants and microorganisms can assimilate.

Large organic phosphorus pool

A pool consisting of microbial plant residue and humidified organic phosphorus that dominates all soil processes.

Soil phosphorus inputs

Sources include animal manures, biosolids, plant residues, mineral fertilizers, and a small amount from atmospheric deposition.

Atmospheric deposition (Phosphorus)

A small input of phosphorus into the soil derived from lightning strikes.

Losses of soil phosphorus

Exits from the soil system include runoff, erosion, crop harvest, and minor leaching.

Mineralization

The process where microbial enzymes catalyze organic phosphorus and turn it into inorganic phosphorus ($P_i$).

Immobilization

The transformation of inorganic phosphorus back into the organic pool through assimilation by microbial biomass.

Apatite (Weathering)

A primary mineral of calcium phosphate that very slowly releases inorganic phosphorus into the soil solution.

Dynamic equilibrium

The state between mineral surfaces, secondary compounds, and inorganic phosphorus, shifting based on environmental changes.

Teragram ($Tg$)

A unit of mass measurement equivalent to $1 \times 10^{12}\,g$ or one megaton ($1 \times 10^6\,\text{tons}$).

Agricultural Phosphorus Input Flux

Approximately $21.5\,Tg$ from phosphate-containing fertilizers and $23\,Tg$ from mining annually.

Animal migration and Phosphorus

A mechanism that historically cycled phosphorus from oceans back to terrestrial systems, which has significantly declined today.

Late Quaternary period

The historical timeframe used to compare relative phosphorus flux before and after megafauna extinctions and human hunting.

Megafauna extinctions

Major declines in large animal populations that contributed to a reduction in the flow of phosphorus back to land.

Labile Phosphorus (Labile P)

The fraction of total inorganic phosphorus ($P_i$) that is available to plants and microorganisms.

Orthophosphate

Specifically $PO_4^{3-}$, the preferred inorganic form of phosphorus for biological uptake.

Phosphoric acid ($H_3PO_4$)

The form phosphorus takes at very low pH values when it is charge-balanced.

Dihydrogen phosphate ($H_2PO_4^-$)

The form of available phosphorus typically found at low pH values between $3$ and $6$.

Hydrogen phosphate ($HPO_4^{2-}$)

The intermediate form of dissociated phosphate as pH rises toward neutrality.

Neutrality Dissociation

The state around pH $7$ where phosphate ($PO_4^{3-}$) is entirely dissociated.

Aluminum dissociation

At low pH, $Al(OH)_3$ becomes $Al^{3+}$, allowing it to combine with phosphate.

Iron dissociation

At low pH in an oxidized environment, hydroxylated iron becomes $Fe^{3+}$ and binds with phosphate.

Variscite

An insoluble form of aluminium phosphate formed at low pH ($3$ to $6$) that removes phosphorus from the labile pool.

Calcium carbonate ($CaCO_3$)

A compound dominant in basic (higher pH) soils that reacts with phosphate to form insoluble minerals.

Apatite (Formation)

An insoluble phosphorus mineral ($Ca_5(PO_4)_3OH$) formed in high pH soils, rendering phosphate unavailable to plants.

Phosphorus availability sweet spot

The soil pH range between $6$ and $7$ where phosphorus is most available as orthophosphate.

Occluded Phosphorus (Occluded P)

Phosphorus that is locked up or associated with calcium/magnesium at high pH or iron/aluminium at low pH.

Silicate clays

Soil components that provide exchange surfaces which can immobilize orthophosphate.

Soil development trend

As soil matures over time, primary mineral phosphorus declines while organic and occluded phosphorus pools increase.

Aquatic Phosphorus recycling

Characterized by the storage of orthophosphate in sediments and chemical/biological transformations in the water stream.

Phosphorus retention factors

Influenced by water flow rate, physical disturbance, and biological transformations.

Flocculation (Phosphorus)

The process where orthophosphate reacts with iron and aluminium in water to form binding particles that deposit in sediment.

Benthic algae

Organisms in aquatic systems that can uptake biologically available phosphorus from the water.

Eutrophication

The deoxygenation of water courses caused by heterotrophic degradation of carbon materials that bloomed due to orthophosphate presence.

Anthropogenic Phosphorus

Human-sourced phosphorus entering the oceans, which was negligible pre-1800 but peaked at about $2.5\,kg/year$ into the modern era.

Fertilizer production (Megatons)

Approximately $14.9\,\text{megatons/year}$ of mined phosphate rock is used for fertilizer production.

Human excreta (Phosphorus flux)

Accounts for approximately $3\,\text{megatons/year}$ of phosphorus, with about half returned to agricultural land.

Rock phosphate acidification

The industrial process used to create super phosphate fertilizers, which transformed global food production.

United States Geological Survey (2009)

The organization that provided early estimates of phosphate rock reserves in the tens of billions of tons.

Morocco and Western Sahara

Referred to as having phosphate reserves at least $10$ times greater than originally conceived in $2011$.

Distribution of Rock Phosphate

Found in specific countries including Algeria, China, Jordan, Morocco, Russia, South Africa, Syria, and the United States.

Legacy soil phosphorus

The accumulation of phosphorus in soils over time; Western Europe has $105\,Tg$, while Asia has $373\,Tg$.

Global legacy soil phosphorus

The total estimated accumulation of phosphorus in soils globally, valued at $815\,Tg$.

Asia Phosphorus crisis

A prediction that Asia has only between $9$ and $20$ years of crop phosphorus supply based on current demand and usage.

Global Phosphorus crisis timeline

The expectation that the world will run very low on phosphorus reserves within the next $100$ years.

Artificial amendment

The continual pumping of large amounts of phosphorus into the plant and animal cycle via crop fertilizers.

Phytoplankton

Marine organisms that assimilate phosphate and pass it through the food chain before dying and releasing it into sediments.

Sol solution derivations

Inorganic forms of phosphorus expressed as various derivations of $PO_4^{3-}$ based on pH level.