Lecture 9

Question 1

Nuclear research gave ecology tools and a model

Answer 1

• Radioactive tracers allowed following fates of chemicals in natural communities
• Manhattan project was classic model for collaborative “Big Science”, a model that ecologists tried to follow with limited success

Question 2

Aspects of selected biogeochemical cycles

Answer 2

• Carbon cycle
• Nitrogen cycle
  
  • Human intervention: N fertilizer for crops
• Phosphorus cycle
  
  • Human interventions: mining, pollution

Question 3

Chemistry of natural world

Answer 3

• Large organic molecules constantly being synthesized, consumed, and broken down
• Chemical elements aren’t created or destroyed, but they move around (cycling)
• Cycle comprises of pools and fluxes
• Stable, long-lived compounds can persist much as elements do

Question 4

C, N and P cycles

Answer 4

• All tied to hydrologic cycle
• Carbon cycle subsumes trophic webs
• N and P are two elements most likely to limit plant productivity
• Key for figures
  
  • Solid black lines: strong natural fluxes
  • Solid red lines: strong human fluxes
    - Dashed black lines: weaker natural fluxes

Question 5

C cycle

Answer 5

• CO2 is gaseous phase, much C in organisms, inactive sedimentary pool of carbonates
• Limiting steps involve balance between creation by photosynthesis and respiration/combustion of organic matter
• Human intervention: Combustion of fossil fuels, land conversion

Question 6

Agricultural impacts on carbon

Answer 6

• Humans deforest land
  
  • Aid to hunting (burning to open and maintain grasslands)
  • Provide land for agriculture (cutting and burning)
  • Remove agricultural waste
  • In N. America, easternmost prairies would revert to forest without fire
• Important phenomenon since the dawn of agriculture
• Carbon sequestered in trees is released by fire

Question 7

Deforestation in the US

Answer 7

• 1620s: Forest mostly cover
• 1920s: Forest mostly eliminated

Question 8

Decadal losses in global forest over last three centuries

Answer 8

• Temperate forests on decline from 1900s
• Temparate regrowth from 2000s onwards
• Tropical on decline, mass deforestation

Question 9

Annual deforestation

Answer 9

• Peak of deforestation in tropical countries

Question 10

Tropical forests contain great stores of carbon

Answer 10

• Near maximum: Indonesian Kalimantan swamp forest on peat soils
  
  • Living plants: 600 tonnes/hectare
  • Dead plant material in soil(peat): 340 tonnes/ha
• Usually too wet to burn, logging causes drying
• If forest burns, peat burns too

Question 11

Human effects on carbon budget

Answer 11

• Larger carbon compounds oxidized to CO2, released into atmosphere
• Current annual rates of CO2 release
  
  • Fossil fuel burning: 6 billion tonnes
  • Deforestation: 1.6 billion tonnes
• Atmospheric CO2 from 280 ppm to 417 ppm
• Strengthening greenhouse effect

Question 12

N cycle

Answer 12

• Mostly gaseous compounds, highly soluble, minimal sedimentary pools
• Limiting steps involve converting inert N2 gas, which plants can’t use into usable soluble nitrate or ammonium
• Human intervention: Combustion of fuels, use of energy to make synthetic fertilizers

Question 13

Human intervention in nitrogen cycle

Answer 13

• An atmospheric cycle
• Anthropogenic reactive N inputs from fuel combustion now exceed natural production rates (in industrial areas, rainwater now a dilute fertilizer)
• Ecosystems being enriched
  
  • Fast, growing, weedy plants favored
  • Nitrate buildup in groundwater a hazard in agricultural areas
  • Eutrophication of coastal waters, anoxia

Question 14

P cycle

Answer 14

• Gases not important, most compounds minimally soluble, sedimentary pools dominate, end up in ocean sediments
• Limiting steps involve weathering of rocks in soil, geological uplift
• Human intervention: Mining phosphate rock for fertilizer, fishing, sewage, agricultural runoff, erosion

Question 15

Phosphorus chemistry 101

Answer 15

• No gaseous forms, mostly in rocks
• Made available through weathering, geological uplift, mining
• Atmospheric dust sometimes important input
• Phosphate technically soluble, but can be bound by soil components; mycorrhizal fungi help pull it into solution so plant roots can get it

Question 16

Human intervention in phosphorus cycle

Answer 16

• A sedimentary cycle (slow)
• We can’t make P fertilizer; must mine phosphate rich rocks ( + guano deposits)
• Lost from terrestrial systems by runoff, erosion, over-application of fertilizers: eutrophication of rivers and lakes
• Much ends up back in marine sediments

Question 17

Phosphate rock for fertilizer in agriculture

Answer 17

• Mostly sedimentart rock (old seabed, uplifted)
• Biggest known reserves: Morocco, US, South Africa, Jordan, China, Russia, Senegal
• Depletion of reserves estimated to be within/in 40-400 years
• Offshore deposits to become targets

Question 18

Best seabird guano industry: islands off coast of Peru

Answer 18

• Seabirds nest on islands because island lacks predators
• Seabird colonies best developed where big fish populated
• Fish populations best developed where cold water upwelling
• Upwelling brings P-rich to surface into food chain
• Dry climate means guano not rapidly leached by rain