Lecture 24 - Nutrient Cycles

Question 1

The Earth is an __ with respect to energy input (energy is constantly supplied by the sun).

Answer 1

open system

Question 2

The Earth is a ___ with respect to nutrient input (ignoring the periodic bombardment by material from outer space).

Answer 2

closed

Question 3

What are nutrients? give an example. A

Are they all directly available to all organisms?

Answer 3

Nutrients are elements used for growth of organisms.
e.g. Nitrogen is one essential element – it exists in many chemical forms in the environment.

No.

Question 4

The conversion of one form of a nutrient to another involves ___

Answer 4

nutrient cycling

Question 5

Which nutrients are in greater demand relative to supply in freshwater plants?

Answer 5

Nitrogen, potassium, phosphorus, etc..

Question 6

What are macronutrients?

Answer 6

C, H, N, O, P

e.g. P is used in the synthesis of DNA, RNA, and ATP

Question 7

What nutrients are sometimes in high demand?

Answer 7

Sometimes in high demand: SI, CA, Mg, Na, K, S, Cl, Fe

e.g. Si is used in diatoms to create their cell walls

Question 8

Name some trace nutrients.

Answer 8

Trace nutrients: Mn, Zn, Cu, Mo, Co

e.g. Mo is needed for several enzymatic reactions, particularly those involved in nitrogen acquisition and fixation

Question 9

From where do autotrophic organisms obtain nutrients? (3)

Answer 9

1. Weathering of Earth’s crust
2. Taken out of Atmosphere
3. Recycled from other organisms

Question 10

Why are ecosystem ecologists interested in nutrient cycling?

Answer 10

1. Some nutrients limit primary productivity.
   nutrients limit secondary productivity, affect diet choice. 2. Can affect our growth rate, behavior, how they control primary production.
2. Human activities are domination the cycles of many nutrients.

Question 11

Give examples of reservoir or pools of nutrients

Answer 11

e.g. primary producers are a reservoir of N, the atmosphere is a reservoir of C (as CO2) (units of mass)

Question 12

Define fluxes

Answer 12

The movement of material from one reservoir to another (units of mass/time) - material enters and leaves a reservoir

Question 13

What is Nitrogen used for? Where is Nitrogen mostly rare? Abundant?

Answer 13

N is an essential constituent of amino acids, proteins, nucleic acids, chlorophyll

It is rare in the earth’s crust, but makes up 79% of the atmosphere (N2) – only some bacteria can convert N2 to a useable form.

Question 14

Some ecosystems rely almost exclusively on ___ whereas others rely on nutrients from ___.

Answer 14

recycled nutrients

outside sources

Question 15

Write the equation for Mass balance approach.

Answer 15

Mass balance approach: Input - Output = Change in storage

Question 16

Describe the Cycles of input and output of nutrients in:

1. Forests, grasslands, oceanic biome
2. Intensive agriculture
3. Industrial agroecosystems, upwelling regions

Answer 16

1. Forests, grasslands, oceanic biome
   low nutrient input and export
   high cycling rate
2. Intensive agriculture
   Intermediate import/export
   manure cycling
3. Industrial agroecosystems, upwelling regions
   high nutrient input & export
   low cycling rate

Question 17

What is nitrogen fixation?

Answer 17

When nitrogen binds to other elements that make it usable.

During nitrogen fixation N2 is reduced to ammonia and ammonium by bacteria

Question 18

Compare the fixation of N2 by bacteria and humans.

Answer 18

humans are fixating the same amount as bacterias

Question 19

Describe the Phosphorus Cycle

Answer 19

1. Essential for energetics (ATP) and structure of organisms.
2. No variety of chemical forms
   essentially: phosphate (PO4 3-)
3. No substantial atmospheric pool
4. Main pools in mineral deposit and marine sediments -> weathering important

Question 20

Humans move around __ and __

Answer 20

N

P

Question 21

P or N surplus can lead to ___

Answer 21

Algal blooms

Question 22

What leads to P surplus? Where is it stored?

Answer 22

P surplus (Stored in soil or run-off in surface waters )  =   annual P inputs  (fertilizer , livestock manure) -  
P removed (harvested crops)

Question 23

When extra nutrients come down into aquatic systems they often lead to ___

Answer 23

Eutrophication

Question 24

Give an example of eutriphication

Answer 24

Algal bloom → block of sunlight, die off, and decay by bacteria

Question 25

What are Zones of hypoxia?

Answer 25

no oxygen (in water)

Question 26

Why don’t all the nutrients end up on the ocean floor?

Answer 26

They get absorbed in soil

Question 27

Humans need phosphate to use energy from carbon. Explain where our phosphate comes from? Where will it go?

Answer 27

Geological uplifting -> weathering from rocks -> phosphate in soil -> leaching into ocean -> Sedimentation at the bottom -> geological uplifting.

It will go back in the soil in form of waste, which decomposers break into phosphate.

Question 28

What form(s) of nitrogen can plants use?

Answer 28

N-fixated
Ammonium: NH4+
Nitrate: NO3-
Nitrite: NO2

Question 29

How have humans altered the nitrogen cycle? The phosphorous cycle?

Answer 29

• Industrial N2 fixation used to produce crop fertilizer; fixes 80 x 1012 gN/year
• Fossil fuel consumption and release of N through land use and biomass burning liberates N from biological and geological storage reservoirs = 70 x 1012 g N/year

Phosphate surplus from agriculture.

Eutrification.