Lecture 24 - Nutrient Cycles Flashcards Preview

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

open system


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



What are nutrients? give an example. A

Are they all directly available to all organisms?

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



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

nutrient cycling


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

Nitrogen, potassium, phosphorus, etc..


What are macronutrients?

C, H, N, O, P
e.g. P is used in the synthesis of DNA, RNA, and ATP


What nutrients are sometimes in high demand?

Sometimes in high demand: SI, CA, Mg, Na, K, S, Cl, Fe
e.g. Si is used in diatoms to create their cell walls


Name some trace nutrients.

Trace nutrients: Mn, Zn, Cu, Mo, Co
e.g. Mo is needed for several enzymatic reactions, particularly those involved in nitrogen acquisition and fixation


From where do autotrophic organisms obtain nutrients? (3)

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


Why are ecosystem ecologists interested in nutrient cycling?

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.
3. Human activities are domination the cycles of many nutrients.


Give examples of reservoir or pools of nutrients

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


Define fluxes

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


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

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.


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

recycled nutrients
outside sources


Write the equation for Mass balance approach.

Mass balance approach: Input - Output = Change in storage


Describe the Cycles of input and output of nutrients in:
1. Forests, grasslands, oceanic biome
2. Intensive agriculture
3. Industrial agroecosystems, upwelling regions

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


What is nitrogen fixation?

When nitrogen binds to other elements that make it usable.
During nitrogen fixation N2 is reduced to ammonia and ammonium by bacteria


Compare the fixation of N2 by bacteria and humans.

humans are fixating the same amount as bacterias


Describe the Phosphorus Cycle

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


Humans move around __ and __



P or N surplus can lead to ___

Algal blooms


What leads to P surplus? Where is it stored?

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


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



Give an example of eutriphication

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


What are Zones of hypoxia?

no oxygen (in water)


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

They get absorbed in soil


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

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.


What form(s) of nitrogen can plants use?

Ammonium: NH4+
Nitrate: NO3-
Nitrite: NO2


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

• 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.