Biogeochemical Cycles

I. Cycling in Nature

A. The structure of ecosystems is influenced by the availability of nutrients and energy.

B. The elemen ts essential for life tend to move in cycles, meaning they move continually through air, water, soil, rock, and living organisms. These cycles are called nutrient cycles or biogeochemical cycles.

I. Cycling in Nature

C. As nutrients move through biogeochemical cycles they may accumulate in one portion of the cycle and remain there for different periods of time.

D. These temporary storage sites, such as the atmosphere, the oceans, and underground deposits are called reservoirs or sinks.

II. Hydrologic and Carbon Cycles

A. The water cycle is the cycle that often facilitates the other cycles – water is an important way in which nutrients move.

B. Remember these terms from the hydrologic cycle – evaporation, transpiration, runoff, percolation, infiltration, aquifer.

Water cycle Diagram

II. Hydrologic and Carbon Cycles

C. The carbon cycle – remember these important processes:

1. Reservoirs – atmosphere, oceans, rocks, fossil fuel deposits

2. Natural processes that add carbon to the atmosphere – respiration and volcanoes

3. Anthropogenic processes that add carbon to the atmosphere – deforestation, burning fossil fuels

4. Both takes out and adds carbon to the atmosphere – The Oceans! Carbon dioxide can be dissolved into the ocean, and is out gassed from the ocean as temperatures warm. (remember more gas can be dissolved in colder solutions).

5. Natural process that removes carbon from the atmosphere – Photosynthesis

6. Natural process that removes carbon from the ocean – marine shelled organisms (CaCO3)

Carbon Cycle Diagram

D. Carbon Cycle Quick Facts:1.Rock reservoir: YES2.Atmospheric component to cycle: YES3.Influences of man: Increased carbon in

atmosphere by burning fossil fuels and deforestation

4.Organisms need it for: Macronutrient – plants must have it to make glucose, all organisms need glucose

III. Nitrogen Cycle

A. Nitrogen cycles between major reservoirs in the atmosphere, soil, and biosphere (plants and animals).

B. There is no major rock reservoir for nitrogen.C. Nitrogen’s major reservoir is the atmosphere

– and the nitrogen found there is in N2 gas. Organisms can’t use nitrogen in this form.

III. Nitrogen Cycle

D. First, nitrogen fixation happens. Gaseous N2 is combined with hydrogen to make ammonia (NH3). Three different ways nitrogen fixation can happen:

1.Lightening2.Specialized bacteria in the roots of legumes

(nitrogen-fixing bacteria)3.Aquatic cyanobacteria (blue-green algae)

III. Nitrogen Cycle

E. Bacteria use some of the ammonia they produce as a nutrient and excrete the rest to the soil or water. Some of this ammonia is converted to ammonium ions (NH4

+1) – plants can uptake ammonium.

III. Nitrogen Cycle

F. Ammonia and/or ammonium not taken up by plants undergo nitrification. In nitrification, soil bacteria convert most of the NH3 and NH4

+1 to nitrate ions (NO3 -1) which are easily taken up by the roots of plants.

G. Plants use nitrate to make amino acids, proteins, nucleic acids, and vitamins.

III. Nitrogen Cycle

H. Plants and animals return nitrogen-rich organic compounds to the environment by their wastes and when they die. Then, the nitrate (NO3) undergoes a reverse set of steps to again be converted to N2 gas that returns to the atmosphere.

I. The process of ammonification involves vast armies of decomposer bacteria convert the nitrate in organisms’ wastes and bodies into ammonia (NH3)and ammonium (NH4

+1).

J. Then, the process of denitrification specialized bacteria in wet soil and the bottom sediments of aquatic environments convert ammonia and ammonium into N2 gas and nitrous oxide (N2O) gas.

K. The gases are released to the atmosphere to begin the nitrogen cycle again.

L. So the important processes in the nitrogen cycle:

1. Nitrogen fixation – atmospheric N2 to ammonia/ammonium

2. Nitrification – ammonia/ammonium to nitrates that plants can easily use

3. Ammonification – wastes and dead organism nitrates turned into ammonia/ammonium

4. Denitrification – ammonia/ammonium turned back into gases N2 and N2O

III. Nitrogen Cycle

M. Human’s primary two impacts on the nitrogen cycle are

1.“Fixing” lots of atmospheric nitrogen to make nitrate fertilizers – moving lots more nitrogen from the atmosphere into the soil/organisms.

2.Burning fossil fuels – adds lots of nitric oxide (NO) to the atmosphere, and in the atmosphere this is converted to nitrous oxide N2O

N. Nitrogen Cycle Quick Facts:1.Rock reservoir: NO2.Atmospheric component to cycle: YES3.Influences of man: Haber process greatly

accelerated the conversion of atmospheric nitrogen to bioavaible “plant” nitrogen

4.Organisms need it for: Must have it to make DNA, proteins

IV. Sulfur Cycle

A. Much of the world’s sulfur is stored underground in rocks and minerals. Sulfur cycles between the rocks, atmosphere, and living organisms.

B. Sulfur enters the atmosphere through volcanic eruptions and anaerobic decomposition in aquatic environments, as well as sea spray, dust storms, and forest fires.

IV. Sulfur Cycle

C. From the atmosphere, sulfur is removed via rain, and falls to the earth.

D. Plants absorb sulfate through their roots, and use sulfur as an essential component of proteins.

E. Humans primarily add more sulfur to the atmosphere in the form of sulfur dioxide (SO2) – it is released when burning coal or refining oil.

Sulfur Cycle Diagram

IV. Sulfur Cycle

F. Sulfur Cycle Quick Facts:1.Rock reservoir: YES2.Atmospheric component to cycle: YES3.Influences of man: Increased sulfur in

atmosphere by large amounts of sulfur dioxide (SO2) released from REFINING oil/gas and burning coal

4.Organisms need it for: Essential component of many proteins

V. Phosphorus Cycle

A. Phosphorus cycles through the crust and earth’s organisms. Phosphorus does not cycle through the atmosphere, so it is a very slow nutrient cycle.

B. The major reservoir for phosphorus is phosphate (PO4 -3)salts in rocks and ocean bottom sediments.

V. Phosphorus Cycle

C. As water runs over exposed phosphorus-containing rocks, the phosphate ions are slowly dissolved out. These phosphate ions can then be absorbed by plants.

D. Phosphorus is used for the phosphate back-bone of DNA, in ATP and ADP, and in bones and teeth of vertebrates.

E. Phosphorus is often the limiting plant nutrient because soils and aquatic bodies of water naturally contain so little of it.

F. Phosphorus is often locked up for millions of years as sediment or in rocks.

G. Humans mine phosphate-containing rocks for use in fertilizers, changing the balance between sequestered phosphorus and available phosphorus.

V. Phosphorus Cycle

H. Phosphorus Cycle Quick Facts:1.Rock reservoir: YES2.Atmospheric component to cycle: NO3.Influences of man: Humans mine phosphate

deposits to make fertilizer, unlocking rock deposits previously unavailable for the system.

4.Organisms need it for: Component of DNA and ATP/ADP, vertebrate bones and teeth

What FORM of N, P, S can plants use?

The forms of phosphorus, sulfur, and nitrogen that plants can absorb (and therefore animals can also use) are nitrate, phosphate, or sulfate. (NO3

,-1 PO4,-3 SO4 -2)

To stay healthy, plants “ATE” their nutrients!