Biogeochemical Cycles. Environment 100 Thursday, May 17, 2012

Transcription

1 Biogeochemical Cycles Environment 100 Thursday, May 17, 2012

2 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

3 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

4 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

5 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

6 Cycling between systems, many scales Seconds Time Centuries O r g a n i s m CO H 2 CO 3 H + + HCO - 3 2H + + CO 2-2(atmos) CO 2(aq) + H 2 O 3 Molecular Space Region

7 Hydrologic cycle: the great pump!

8 Earth s Water

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10 Available freshwater resources per capita

11 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.

12 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

13 Water Use

14 Different countries use water differently

15 Different countries use water differently

16 World water use and irrigation Worldwide, ~70% of water use is for agriculture

17 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

18 Areas of unsustainable water withdrawals leads to surface water diversions & groundwater deplevon Globally, 15-35% of water withdrawals are unsustainable.

19 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 colorado_river_grand_canyon.jpg

20 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

21 Flows at the mouth of the Colorado

22 The Colorado River, Demand exceeds supply

23 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

24 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

25 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. We should reduce farm consumpvon by 20% to double urban water supply 50% 50% 3. We should not do this 1 2

26 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

27 Biogeochemical Cycles Outline What are biogeochemical cycles Water Cycle Carbon Cycle Fast and Slow Biofuels and Tilman s principles Nitrogen Cycle Haber- Bausch Process

28 1 Gt = 10 9 metric tons = grams 1 Gt = 40,000 aircraft carriers

29 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 CO 2 is a crivcal gas: Taken up by plants in photosynthesis Released by plants and animals in respiravon Released during decomposivon and fires Greenhouse gas

30 The fast carbon cycle: DRIVEN BY Days to thousands of years Movement of C thorough life forms on earth (biosphere) Photosynthesis converts atmospheric CO 2 to carbohydrates (sugars) RespiraVon and fire breaks down sugars to get energy (plants, animals, decay), and CO 2 is released to atmosphere PHOTOSYNTHESIS CO 2 + H 2 O + energy = CH 2 O + O 2 carbon dioxide + water = sugar and oxygen

31 Slow Carbon Cycle: Between rocks, soil, ocean, atmosphere, biosphere, in millions of years 1) Atmospheric C0 2 +H 2 0 à carbonic 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:

32 Which of the following is not an example of the slow carbon cycle 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 25% 25% 25% 25%

33 Changes in Atmospheric C0 2 But matter cannot be created or destroyed. Where is the C coming from?

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35 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.

36 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

37 Two quetsions: How are biofuels related to the fast and slow carbon cycle? How can biofuels be carbon neutral? Are they always carbon neutral?