Biogeochemical Cycles

Something to think about…

• A handful of elements combine to form the building blocks of all known organisms.

• Organisms cannot manufacture these elements and do not “use them up,” so where do essential elements come from?

Objectives:

• Identify the elements of Life

• Identify and describe the flow of elements (“nutrients”) in each biogeochemical cycle.

• Explain the impact that humans have on the biogeochemical cycles.

Two Secrets of Survival: Energy Flow and Matter Recycling

• An ecosystem survives through a combination of energy flow and matter recycling.

• Unlike the one-way flow of energy, matter is recycled within and between ecosystems.

• As matter moves through these cycles, it is never created or destroyed —just changed.

Why is it important that matter is recycled?

• They are required to build and maintain an organism

Elements of Life

Essential Elements

• 24 elements are required for life• Macronutrients are required in LARGE

quantities– carbon, hydrogen, nitrogen, oxygen,

phosphorus, and sulfur.

• Micronutrients are required in small/medium quantities, or not at all in some organisms– Copper, sodium, iodine

How does matter move through the biosphere?

• A biogeochemical cycle is the complete path a chemical takes through the Earth’s four major reservoirs:

• atmosphere• hydrosphere (oceans, rivers, lakes,

groundwaters, and glaciers)• lithosphere (rocks and soils)• biosphere (plants and animals)

• Chemicals enter storage compartments - sinks

Biogeochemical Cycles in Ecosystems

• Biological Processes– any and all activities performed by living organisms;

includes eating, breathing, “burning” food, and eliminating waste

• Geological Processes– include volcanic eruptions, the formation & breakdown

of rock, and major movements of matter within and below the surface of the earth

• Chemical / Physical Processes– include the formation of clouds and precipitation, flow

of running water, and the action of lightning

Hydrologic (Water) Cycle

Carbon Cycle

• Carbon is vital for life but is not abundant

• Enters biological cycles through photosynthesis to produce organic forms of carbon

Carbon Cycle in a Pond

Fossil Fuels• Lack of oxygen or low

temperatures may prevent decomposition of dead organisms

• Burial in sediments over thousands or millions of years transforms the stored organic carbon into coal, oil or natural gas

Global Carbon Cycle

Nitrogen Cycle

Nitrogen Cycle

• Essential for manufacturing proteins and DNA

• Although 80% of atmosphere is molecular nitrogen, it is unreactive and cannot be used directly

• Nitrogen fixation converts nitrogen to ammonia or nitrate

Nitrogen Fixation

• Some organisms have a symbiotic relationship with nitrogen fixing bacteria

• Found in root nodules in some plants, or in the stomach of some herbivores

• Nitrogen fixation also occurs through lightning and industrial processes

Denitrification

• When organisms die, denitrifying bacteria convert organic nitrogen to ammonia, nitrate, or molecular nitrogen

Nitrogen Cycle

Global Phosphorus Cycle

Phosphorus Cycle

• No gaseous phase• Slow rate of transfer• Released by erosion of exposed rock• Absorbed by plants, algae, and some

bacteria• Exported from terrestrial ecosystems by

runoff to oceans• May be returned through seabird guano

Phosphate Mining

• Impact on landscape by open-pit mining

Sulfur Cycle In a Forest Ecosystem

Includes gaseous forms (sulfur dioxide and hydrogen sulfide);cycles much faster than calcium

Calcium Cycle in a Forest Ecosystem

Soluble in water and easily lost through runoff

Remember…

• Biogeochemical cycles of matter pass the same atoms and molecules around again and again.

• If you interrupt thecycling, how doesthis affect theecosystem?

Case of the missing carbon!

– Analysis shows contribution of 8 .5 bill. tons into the atmosphere but less than ½ stays there…where does it go?

– 7 billion from fossil fuels and 1.5 billion from deforestation

Case of the missing carbon!

– Appears oceans are acting as carbon sinks as are forests and grasslands.

– But which area is more critical, and which one dominates.

– Will these blessings last?• If they stop functioning we could face drastic changes

even before 2050.

Case of the missing carbon!– Global tests of CO2 show less in the north than the south

despite larger northern outputs

– Why is this the case?

– If land plants are doing the work then there should be a corresponding oxygen increase.

– If it is dissolving in the oceans then there should be no added oxygen.

Case of the missing carbon!

– Results (best guess):• Ocean is soaking up 2.4 billion tons globally

• Land plants do the most work in the northern hemisphere

– Forests literally breath in the carbon but appetite changes dramatically due to season, amount of sunlight, rainfall, and age of forests

• Marine organisms undergo photosynthesis as well

• So that leaves about 2.9 units unaccounted for between these groups.

Case of the missing carbon!

– Biggest threats:• Decline in forest growth

• Killing of ocean phytoplankton due to rising sea temperatures

• Death of forests due to spread of disease and insects

• Melting permafrost layer

• Land clearing for development and agriculture

• Ofcourse continued output of carbon from fossil fuel burning