Phosphorus Cycle

Question 1

Phosphorus Cycle Definition

Answer 1

• cyclic movement of phosphorus in different chemical forms from environment to organisms & then back to environment, in the biosphere

Question 2

Where does the cycle operate?

Answer 2

Mainly operates between land & water, not in the atmosphere

Question 3

How does phosphorus enter the atmosphere?

Answer 3

Phosphorus does enter atmosphere in very small amounts when dust is dissolved in rainwater or sea spray.

Question 4

Weathering

Answer 4

Phosphorus rocks in mountains are slowly weathered by natural forces including rainfall & this weathering brings phosphorus to terrestrial & aquatic habitats

Phosphorus may enter soil & water when rocks erode. Small amounts of phosphorus dissolve as phosphate, which moves into soil

Question 5

Assimilation

Answer 5

Producers on land & in water take up inorganic phosphate & assimilate phosphorus into their tissues as organic phosphorus

Question 6

Decomposition + Mineralization

Answer 6

Waste products & eventual dead bodies of these organisms are decomposed by fungi & bacteria, which causes mineralization of organic phosphorus back to inorganic phosphate

Question 7

How does phosphorus end up in the ocean?

Answer 7

Some phosphorus washes off the land & ends up in the ocean.

Question 8

Sedimentation

Answer 8

Many phosphate salts are not soluble in water, they sink to bottom & accumulate as sediment in ocean

Question 9

Uplift

Answer 9

Over time, geologic forces can lift these ocean layers up & they become mountains

Question 10

Geological Uplift

Answer 10

Phosphorus tightly held by soils, so it is not easily leached from soils & into bodies of water

Question 11

Why is phosphorus a limiting nutrient?

Answer 11

Very little dissolved phosphorus is naturally available in streams, rivers, & lakes, as a result it is a limiting nutrient in many aquatic systems

Question 12

Phosphate mining

Answer 12

Humans mine phosphate sediments from mountains to produce fertilizer

Question 13

Human Effect - Runoff / Leaching

Answer 13

Excessive amounts of fertilizer applied to lawns, gardens, & agricultural fields can enter terrestrial & aquatic ecosystems through runoff or leaching

Question 14

Eutrophication

Answer 14

• Excess nitrogen & phosphorus can cause rapid growth of producers such as algae in aquatic ecosystems
• Increase in algae, aka algal bloom, can deplete an aquatic ecosystem of important nutrients such as oxygen, which fish & other aquatic organisms depend
• When algae dies, decomposition occurs which consumes large amount of oxygen
• Water becomes low in oxygen, hypoxic.
• When oxygen concentrations become so low, it kills fish & other aquatic animals & it is known as a dead zone - AKA Eutrophication
• Dead zones occur around the world, including where the Mississippi River empties into the Gulf of Mexico (affects tourism and fishing industries)

Question 15

Human Usage of Phosphorus in ____ is causing more dead zones

Answer 15

2nd major source of phosphorus in waterways is from use of household detergents – causing more dead zones

Question 16

Major reservoirs of phosphorus

Answer 16

rock & sediments that contain phosphorus-bearing minerals