Nutrient Cycles II: Sulfur and Phosphorus

Question 1

Importance of studying nutrient cycles?

Answer 1

All living organisms are made up of chemical elements

Question 2

What is the importance of studying nutrient cycles ?

Answer 2

• We can describe ecosystem functioning or community organization by looking at chemical/nutrient flow through the system
• Chemical Nutrients (C,P,S,Fe,etc.) influence primary & secondary productivity of species, communities
• Humans are altering nutrient pools and nutrient cycles, so it is important to measure and understand this

Question 3

What is Biogeochemical (nutrient) Cycle?

Answer 3

-Movement of chemical elements around an ecosystem via physical and biological processes

Question 4

What is the purpose of these biogeochemical (nutrient) cycles?

Answer 4

• Nutrients cycle and recycle throughout the ecosystem, and get used over and over again
• For a sustainable ecosystem, nutrient input should equal output but humans are altering balance, either by removal or addition of nutrients

Question 5

Local Nutrient Cycle Characteristics

Answer 5

• small scale (population or community)
• Phosphorus
• Do not include gaseous phase

Question 6

Global Nutrient Cycle Characteristics

Answer 6

• Large scale (ecosystem, biosphere)
• O, N, C
• Include gaseous (volatile) phase
• Summation of local cycles

Question 7

What is Pool?

Answer 7

Mass of element or molecule in a given location or chemical state (units of mass)
-I.e. amount of S in the atmosphere or amount of iron sulfide (FeS2) in the ocean sediment

Question 8

What is Flux?

Answer 8

Rate of movement into or out of pool (units of mass/ time)

Question 9

What is Mean Residence Time (MRT)?

Answer 9

Pool divided by flux, average amount of time spent by a single molecule in the pool (units of time)

Question 10

What is Turnover Rate?

Answer 10

Inverse of MRT, cycles through pool per unit time (units of time -1)

Question 11

How do Nutrients Enter an Ecosystem?

Answer 11

Physical Processes and Biological Processes

Question 12

What are the two Physical Processes?

Answer 12

Meteorological and Geological

Question 13

How do nutrients enter through meteorological?

Answer 13

• Dissolved matter in rain, snow
• Atmospheric gases
• Dust blown by the wind

Question 14

How do nutrients enter through geological?

Answer 14

• Weathering of rocks, soil

- Elements in water drainage

Question 15

How do nutrients enter through Biological processes?

Answer 15

movement of animals between ecosystems

Question 16

Important Facts of Nutrients Entering an Ecosystem

Answer 16

• All nutrients sourced from either minerals in rocks or gases from the atmosphere
• Nutrients taken up by organisms, changed into different forms
• Nutrients repeatedly cycle through an ecosystem

Question 17

What is the Sulfur Cycle?

Answer 17

Processes by which sulfur moves to and from the environment (minerals, atmosphere) and living organisms

Question 18

How is Sulfur an essential element?

Answer 18

• Key component in proteins

- Hydrogen sulfide (H2S) for anoxygenic photosynthesis

Question 19

What are the 6 forms of Sulfur?

Answer 19

1. Organic sulfur (contain C backbone with H)
2. S^2- (sulfide)
3. SO4^2- (sulfate)
4. H2S (hydrogen sulfide)
5. SO2 (sulfur dioxide)
6. (CH3)2S (dimethyl sulfide,DMS)

Question 20

Dimethyl Sulfide (DMS): Lovelock 1987

Answer 20

• Sourced from blooms of phytoplankton on ocean surface
• Distinct smell to gas- “smell of the shore” or “smell of the sea”
• Seabirds have olfactory cue to find blooms by scent of gas
• Large source of sulfur that goes into atmosphere as gas
• DMS helps drive cloud formation, which may help cool the planet by blocking solar radiation
• DMS production may increase under climate change

Question 21

What are Some Human Alterations to the Sulfur Cycle?

Answer 21

• Acid Rain
• Burning of fossil fuels has impacted S cycle more than any other nutrient cycle
• Human produce 160% of natural S emissions to atmosphere

Question 22

What is the Phosphorus (P) Cycle?

Answer 22

Processes by which phosphorus moves to and from the environment and living organisms
-P compounds are usually solids, so atmosphere is not a significant pool or step of P cycle

Question 23

How is Phosphorus an Essential Element?

Answer 23

• ATP & DNA backbone

- P is limiting for primary producer and microbial growth

Question 24

What are the Biological Inputs of P Cycle?

Answer 24

From organisms (short, local)

Question 25

What are the Physical Inputs of P Cycle?

Answer 25

From weathering of rock, sol (long-term, global)

Question 26

How is P limiting in Freshwater, Tropical Soils?

Answer 26

• High precipitation in tropics leaches P from soil
• When P binds with soil & sediment, not available for uptake
• Low pH of tropical soil = high binding affinity to other compounds
• Humans have impacted the P cycle

Question 27

What happens at pH above 5.5?

Answer 27

Phosphates binds with calcium and these compounds are water soluble

Question 28

What happens at pH below 5.5?

Answer 28

Aluminum (Al3+) is abundant and will bind with phosphates (non-water soluble)

Question 29

Example Human Alterations of P Cycle?

Answer 29

-Mining Guano in the Chincha Islands off the Central Coast of Peru (1860)