Biogeochemical Cycles - 1

Class Lecture Goals

1. What are systems?

2. What are biogeochemical cycles?

3. Why are they important?

4. What is common about them?

5. Carbon and nitrogen cycles

6. Focus on the Water Cycle (Monday)

Today’s Topic: “Did Logging Worsen Floods?”

• State Senate Committee• Weyerhaeuser Co.• State DNR• David Montgomery• Phil Mote• Ideas

– System: Watershed– Cumulative effects– Climate Change

What is a system?

• System: a collection of matter, parts, or components which are included inside a specified, often arbitrary, boundary. Example: Ecosystem

• Systems often have inputs and outputs.• For dynamic systems, by definition, one or more

aspects of the system change with time.– Example of a simple dynamic system: bathtub or your

‘bank’ account.

• The boundary of a dynamic system is chosen for convenient conceptual separation for the system

PoolFlux

Carbon dioxide

C-pool

SugarSugar

Night

Reading Assignments• Examine this web page (http://www.cses.washington.edu/cig/pnwc/cc.shtml)

Select the true statement from below for the PNW: Climate

change will

1 2 3

0% 0%0%1. Increase precipitation & snowpack

2. Increase temperature & snowpack

3. Increase precipitation & decrease snowpack

Answer Now!

10

What are biogeochemical cycles?• Earth system has four parts

– Atmosphere– Hydrosphere– Lithosphere– Biosphere

• Biogeochemical cycles: The chemical interactions (cycles) that exist between the atmosphere, hydrosphere, lithosphere, and biosphere.

• Abiotic (physio-chemical) and biotic processes drive these cycles

• Focus on carbon and water cycles (but could include all necessary elements for life). N - cycle weakly touched on!

What is common amongst them?

• Each compound (water, carbon, nitrogen) typically exists in all four parts of the Earth System

• There are – ‘Pools’– Fluxes in and out of pools– Chemical or biochemical transformations

• Transformations – are important– can lead to positive & negative consequences

Transformations

Examples of Transformations1. Carbon cycle: Organic compounds to CO2

(processes: respiration, decomposition, or fire)2. Carbon cycle: CO2 to organic compounds (process:

photosynthesis)3. Nitrogen cycle: N2 to NO3 (atmospheric nitrogen to

plant utilizable nitrate) (process: N-fixation)4. Nitrogen cycle: N2 to NH3 (plant utilizable ammonia)

(process: Haber-Bosch Industrial N-fixation) 5. Water cycle: Liquid water to water vapor (process:

evaporation and evapo-transpiration)6. Water cycle: Water vapor to liquid water (process:

condensation)

5000

http://www.epa.gov/climatechange/kids/carbon_cycle_version2.html

Carbon Cycle

Carbon Cycle Data

• Burning of fossil fuels

• Land conversion

• Cement

• Role of Oceans

• Role of terrestrial plants (trees & soils)

760

59

Lithosphere

Changes in Atmospheric C02 - 1

Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/cgg/trends)

Changes in Atmospheric C02 - 2

http://www.whrc.org/resources/online_publications/warming_earth/scientific_evidence.htm

Key Aspects of the Carbon Cycle

• Carbon is the skeleton of all life.• Carbon dioxide is a critical gas:

– Taken up by plants in photosynthesis– Released by plants and animals in respiration– Released during decomposition (and fires)– Greenhouse gas (greenhouse effect - your car

in the sun)

Question: Photosynthesis is an example of a pool

1 2

0%0%

1. True

2. False

Answer Now!

10

Nitrogen Cycle

http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm

Forms of Nitrogen (N2)• N2 - inert gas, 78% of the atmosphere• NO, N20, NO2 - other gases of nitrogen, not directly

biologically important. Part of the gases found in smog.

• NO3- (nitrate) and NH4

+ (ammonium) -- ionic forms of nitrogen that are biologically usable.

Nitrogen Cycle

http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm

Forms & Sources of biologically available nitrogen (N2)

For plants• NO3

- (nitrate) • NH4

+ (ammonium) • Sources: N-fixation by plants (N2 to NH3 and N2 to NO3),

lightening, bacteria decomposition of organic N (amino acids & proteins)

For animals• Organic forms: amino acids and proteins (from plants or

other animals)

Nitrogen Cycle

http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm

Losses of nitrogen from system

• In bogs, lakes (places of low oxygen), NO3- is converted

to N2 by bacteria (get their oxygen from the NO3)• Volatilization of NH4

+ (urea) to ammonia gas (NH3) - warm, dry conditions.

• Leaching of NO3- (nitrate)

• Erosion• Fire (combustion)

Nitrogen Sources over time

Nitrogen Cycle: Key Points

• Nitrogen is in the atmosphere as N2 (78%)• N2 is an inert gas and cannot be used by

plants or animals• N2 can be converted to a usable form via

– Lightening – N-fixing plants and cyanobacteria– Industrial process (energy intensive)

• Nitrogen limits plant growth• Nitrogen is easily lost from biological

systems

Summary

• 1. What are systems?

• 2. What are biogeochemical cycles?

• 3. Why are they important?

• 4. What is common about them?

• 5. Carbon and nitrogen cycles