Phosphorus Cycle

Question 1

what is the phosphorus cycle?

Answer 1

the movement of atoms and molecules containing the element phosphorus between sinks and sources

Question 2

what are the major reservoirs of phosphorus?

Answer 2

rock and sediments that contain phosphorus-bearing minerals

Question 3

what makes the phosphorus cycle unique compared to other biogeochemical cycles?

Answer 3

there is no atmospheric component in the phosphorus cycle
it is also very slow compared to the carbon, hydrologic, and nitrogen cycles

Question 4

what is the limitation of the phosphorus cycle?

Answer 4

because there is no atmospheric component, phosphorus is naturally scarce in aquatic and many terrestrial ecosystems due to the limitations on the return of phosphorus from the ocean to land
this means that in undisturbed ecosystems, phosphorus is the limiting factor in biological systems (plant growth is limited by the availability of phosphorus in the water/soil)

Question 5

what takes a long time in the phosphorus cycle?

Answer 5

it takes a long time for phosphorus minerals to be weathered out of rocks and carried into soil/bodies of water

Question 6

why is phosphorus important?

Answer 6

phosphorus is needed by all organisms for DNA, ATP (energy), and bone and tooth enamel in some animals

Question 7

where can phosphorus be found in an ecosystem?

Answer 7

in mountains, soil, and sedimentation at the bottom of bodies of water

Question 8

what is the process of weathering in the phosphorus cycle?

Answer 8

wind and rain break down rock and release phosphorus as phosphate that is washed away into the soil of terrestrial ecosystems or the water of aquatic ecosystems

Question 9

there is no gas phase of phosphorus, so it travels in:

Answer 9

a solid form called phosphate

Question 10

what are the major natural sources of phosphorus?

Answer 10

weathering rocks that contain phosphorus minerals

Question 11

what are the major synthetic/human sources of phosphorus?

Answer 11

mining phosphate minerals and adding them to products like synthetic fertilizers and detergents/cleaners

Question 12

weathering in the phosphorus cycle is slow, so phosphorus is:

Answer 12

a limiting nutrient in aquatic and terrestrial biomes

Question 13

how does weathering work in the phosphorus cycle?

Answer 13

wind and rain break down rock and phosphate is released and dissolved into water, then rain carries phosphate into nearby soils and bodies of water

Question 14

how does runoff work in the phosphorus cycle?

Answer 14

synthetic fertilizers containing phosphates are added to lawns or agricultural fields, then runoff carries phosphate into nearby bodies of water
phosphates from detergents and cleaners enter bodies of water via wastewater from homes

Question 15

how does assimilation work in the phosphorus cycle?

Answer 15

just like nitrogen, phosphorus is absorbed by plant roots and assimilated into tissues
animals assimilate phosphorus by eating plants or other animals that have eaten plants

Question 16

how does excretion/decomposition work in the phosphorus cycle?

Answer 16

animal waste, plant matter, and other biomass is broken down by bacteria/soil decomposers that return phosphate to soil

Question 17

what is a mini-loop in the phosphorus cycle?

Answer 17

assimilation and excretion

Question 18

what is a mini-loop in the nitrogen cycle?

Answer 18

assimilation and ammonification

Question 19

how does sedimentation work in the phosphorus cycle?

Answer 19

phosphate doesn’t dissolve very well into water and much of it forms solid bits of phosphate that fall to the bottom as sediments

Question 20

what happens to phosphorus sediments over time?

Answer 20

they can be compressed into sedimentary rock over long periods of time by the pressure of overlying water

Question 21

what is geological uplift?

Answer 21

tectonic plate collision forcing up rock layers that form mountains

Question 22

how is geological uplift significant in the phosphorus cycle?

Answer 22

the phosphorus cycle can start over again with weathering and release of phosphates from rock
(loop of marine sediments to geological uplift to weathering to marine sediments)
completes the return of phosphorus from aquatic biomes to terrestrial biomes

Question 23

what causes eutrophication? why do those cause eutrophication?

Answer 23

eutrophication can occur from fertilizer runoff and human/animal waste contamination
extra input of nitrogen and phosphorus (excess nutrients) fuels algae growth because they’re limiting nutrients in aquatic ecosystems

Question 24

describe the positive feedback loop of eutrophication

Answer 24

• algae bloom covers surface of water, blocking sunlight and killing plants below the surface
• algae eventually dies off and bacteria that break down dead algae use up the oxygen in the water because decomposition is an aerobic process
• lower oxygen levels (dissolved oxygen) in water kills aquatic animals like fish
• bacteria use up even more oxygen to decompse dead aquatic animals
• less oxygen → more dead organisms → more bacterial decomposition → less oxygen