Biogeochemical  Cycles  

Environment  100    Thursday,  May  17,  2012  

But  first,  lets  talk  about  Tuesday  •  What  did  you  learn?    What  did  it  connect  to?  What  were  each  speaker’s  take  home  points?    

•  Please  talk  with  one  another  in  groups  of  THREE.  Ensure  that  you  understand  the  key  points  of  the  speakers.      

•  Each  of  you  should  choose  one  speaker  (all  covered  by  each  group  of  three)  and  write  down  1-­‐3  sentences  summarizing  their  talk.    

•  Include  your  name  and  turn  this  in  

Biogeochemical  Cycles  Outline  

•  What  are  biogeochemical  cycles  •  Water  Cycle  •  Carbon  Cycle  

– Fast  and  Slow  Cycle  – Biofuels  and  Tilman’s  principles  

•  Nitrogen  Cycle  – Haber-­‐Bausch  Process  

What  are  biogeochemical  cycles?  •  Earth  system  has  four  parts  

–  Atmosphere  –  Hydrosphere  –  Lithosphere  –  Biosphere    

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

 •  Abio0c  (physio-­‐chemical)  and  bio0c  processes  

drive  these  cycles  

What  is  common  amongst  them?  •  Each  compound  (e.g.,  water,  carbon,  nitrogen,  oxygen,  

sulfur,  phosphorus,  mercury,  etc.)  typically  exists  in  all  four  parts  of  the  Earth  System  

•  Biologically  useful  forms  are  oXen  low  •  There  are    

–  ‘Pools’ where  compounds  are  stored  –  Fluxes  in  and  out  of  pools  –  Chemical  or  biochemical  transformaVons  

•  TransformaVons    –  are  important  –  can  lead  to  posiVve  &  negaVve  consequences  

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Molecular Space Region

Organism

Cycling  between  systems,  many  scales  

CO2(atmos) ↔ CO2(aq) + H2O ↔ H2CO3 ↔ H+ + HCO3- ↔ 2H+ + CO3

2- CO2(atmos) ↔ CO2(aq) + H2O

Hydrologic  cycle:  the  great  pump!  

Earth’s  Water  

Available  freshwater  resources  per  capita  

Kuwait  makes  its  water  by  desalinaVng  seawater.  According  to  your  reading,    

1.  This  is  expensive  and  uses  lots  of  energy  so  will  not  be  providing  much  freshwater  in  the  near  future  

2.  This  is  expensive  and  uses  lots  of  energy  but  technology  is  changing  so  quickly,  this  is  likely  to  be  the  way  we  meet  our  water  needs  in  the  near  future  

3.  The  above  statement  is  wrong.  DesalinaVon  is  currently  impossible.  

Water  Demand  

•  Clean  fresh  water  essenVal  to  human  health,  agriculture,  industry  

•  Humans  appropriate  >  50%  all  FW  •  U.S.  uses  1.3  trillion  liters  (340  billion  gallons)  per  day  – 4330  liters  (1,150  gallons)  per  person  – More  than  any  other  naVon    

Water  Use  

Different  countries  use  water  differently  

Different  countries  use  water  differently  

World water use and irrigation

Worldwide,  ~70%  of  water  use  is  for  agriculture  

Water  is  a  renewable  resource  •  Unlike  energy  resources,  water  can  be  used  over  and  over  •  Natural  hydrologic  cycle  replaces  water  if  natural  systems  are  not  overloaded  

•  Water  is  renewable  but  renewal  takes  Vme  •  Current  rate  is  unsustainable  

Areas  of  unsustainable  water  withdrawals  –  leads  to  surface  water  diversions  &  groundwater  depleVon  

Globally,  15-­‐35%  of  water  withdrawals  are  unsustainable.  

Conflict  over  water…  •  “The  wars  of  the  21st  century  will  be  fought  over  water.” —  Ismail  Serageldin,  Chairman  of  the  World  Water  Commission  

•  Water  scarcity  exacerbates  conflict  – Our  example:  the  Colorado  River  

 http://4.bp.blogspot.com/-8onDIca6T_A/TcBORMKxhAI/AAAAAAAAADQ/QzZy2b-xwj4/s320/colorado_river_grand_canyon.jpg

Colorado  River  •  Water  to  7  states  &  2  countries  •  Colorado  contract  1922  

allocated  water  rights  –  Previous  decade  wekest  in  

>thousand  years!!  

•  CiVes  have  grown  •  Agriculture  has  expanded  •  Water  diversions  could  divert  

enVre  river  flow  •  1944  agreement  with  Mexico:  

water  must  cross  the  border  in  the  river  

 

Flows  at  the  mouth  of  the  Colorado    

The Colorado River, Demand exceeds supply

Lake  Mead  

•  30  miles  SE  of  Las  Vegas  •  Largest  reservoir  in  the  US,  formed  by  water  impounded  by  Hoover  Dam  

•  Could  reach  “dead  pool”  levels  this  decade  •  With  Lake  Powell,  85%  Colorado  River  storage  •  River  flows  expected  to  decrease  10-­‐30%  due  to  climate  change  

Sam Morris/ Sun File photo

Water,  agriculture  and  the  Colorado  River  

•  Los  Angeles  has  a  “dry  year  opVon”  to  transfer  water  from  agriculture  to  urban  use  

•  In  dry  years,  the  city  pays  7000  farmers  to  stop  farming  and  ship  their  water  to  the  city  

•  By  changing  crops  and  rotaVng  fallow  fields,  farmers  hope  to  stay  in  business  while  avoiding  bakles  over  dwindling  water…  

 

According  to  the  Pacific  InsVtute,  farming  used  85%  of  California’s  water  to  produce  2%  of  its  economic  

output.    Reducing  farm  consumpVon  by  20%  per  year  could  double  the  urban  water  supply,  but  those  who  depend  on  agricultural  income  think  this  is  a  bad  idea.    

WHAT  DO  YOU  THINK?  

1 2

50%50%1.  We  should  reduce  farm  consumpVon  by  20%  to  double  urban  water  supply  

 3.  We  should  not  do  this  

Freshwater  Shortages  

•  Clean  drinking  water  and  basic  sanitaVon  ecessary  to  prevent  disease  &  maintain  health  

•  UN  esVmates  at  least  a  billion  people  lack  access  to  safe  drinking  water  and  2.5  billion  don’t  have  adequate  sanitaVon  

•  Result  in  illness:  hundreds  of  millions  and  5  million  deaths  per  year  

Biogeochemical  Cycles  Outline  

•  What  are  biogeochemical  cycles  •  Water  Cycle  •  Carbon  Cycle  

– Fast  and  Slow  – Biofuels  and  Tilman’s  principles  

•  Nitrogen  Cycle  – Haber-­‐Bausch  Process  

1 Gt = 109 metric tons = 1015 grams 1 Gt = 40,000 aircraft carriers

Key  Aspects  of  the  Carbon  Cycle  •  Carbon  is  the  skeleton  of  all  life  &  foundaVon  of  all  food  webs  

–  Forms  lots  of  bonds  (up  to  4  per  atom)  in  huge  array  of  complex  molecules  

–  Bonds  in  carbon  chains  store  lots  of  energy  à  energy  released  when  bonds  are  broken  

–  This  energy  makes  carbon  an  excellent  source  of  fuel  for  living  things  

•  FoundaVon  of  fossil  fuels  •  CO2is  a  criVcal  gas:  

–  Taken  up  by  plants  in  photosynthesis  –  Released  by  plants  and  animals  in  respiraVon  –  Released  during  decomposiVon  and  fires  –  Greenhouse  gas  

The  fast  carbon  cycle:  DRIVEN  BY  PHOTOSYNTHESIS  

CO2 + H2O + energy = CH2O + O2 carbon dioxide + water = sugar and oxygen

•  Days  to  thousands  of  years  •  Movement  of  C  thorough  life  

forms  on  earth  (biosphere)  •  Photosynthesis  converts  

atmospheric  CO2  to  carbohydrates  (sugars)  

•  RespiraVon  and  fire  breaks  down  sugars  to  get  energy  (plants,  animals,  decay),  and  CO2  is  released  to  atmosphere  

 

Slow  Carbon  Cycle:  Between  rocks,  soil,  ocean,  atmosphere,  biosphere,  in  millions  of  years  

1)  Atmospheric  C02  +H20  àcarbonic  acid  in  rain.  Acid  dissolves  rocks  releasing  ions.  Rivers  carry  to  ocean.    Organisms  combine  calcium  and  bicarbonate  to  make  shells.  Organisms  die  and  sink.  Over  Vme,  shells  and  sediment  turn  to  rock—storing  C  in  stone.    

2)  Living  things  get  embedded  in  layers  of  mud.  Heat  and  pressure  compress  the  mud  and  carbon.  If  dead  maker  builds  up  faster  than  it  can  decay,  this  maker  becomes  oil,  coal,  or  natural  gas.    

3)  C  returned  to  atm  through  volcanoes  &  ocean  atm  diffusion  

Images: http://earthobservatory.nasa.gov/Features/CarbonCycle/images/marble_fossils.jpg

Which  of  the  following  is  not  an  example  of  the  slow  carbon  cycle  

1 2 3 4

25% 25%25%25%1.  Volcanic  erupVon  2.  Heat  and  pressure  

form  pools  of  stored  carbon  

3.  Carbon  dioxide  is  transformed  into  sugar  by  a  plant  

4.  A  phytoplankton  dies  and  sinks  to  the  bokom  of  the  ocean  

Changes  in  Atmospheric  C02  

http://www.esrl.noaa.gov/gmd/ccgg/trends/ http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html

But matter cannot be created or destroyed. Where is the C coming from?

Tilman’s  et  al  2009  

•  “In  a  world  seeking  soluVons  to  its  energy,  environmental  and  food  challenges,  society  cannot  afford  to  miss  out  on  the  global  greenhouse-­‐gas  emission  reducVons  and  the  local  environmental  and  societal  benefits  when  biofuels  are  done  right.    However,  society  also  cannot  accept  the  undesirable  impacts  of  biofuels  done  wrong.”  

Tilman’s  principles:  biofuels  done  right  

Must  be  derived  from  crops  produced  with  A)  low  life-­‐cycle  greenhouse  gas  emissions  that  B)    do  not  compete  with  food  produc0on  1.  Perennial  plants  growing  on  abandoned/  degraded  farm  

land  2.  Crop  residues    3.  Sustainably  harvested  wood  and  forest  residue  4.  Double  cropping  or  mixed  cropping  5.  Municipal  and  industrial  wastes  

In US, when both direct and indirect emission are taken into account, cellulosic biofuel must offer at least 60% life cycle grenhouse gas reduction relative to conventional gasoline

Two  quetsions:  

•  How  are  biofuels  related  to  the  fast  and  slow  carbon  cycle?  

•  How  can  biofuels  be  carbon  neutral?    Are  they  always  carbon  neutral?