Populations, N, P, Agriculture

Atmospheric N2 Pool
3.9 x 10^21 g
Soil organic nitrogen (fixed N2 pool in the soil): 110 x 10^15 g
Plant N2 Pool
2.5 x 10^15 g
Atmosphere to soil exchange
140 x 10^12 g/yr
1/1000 of the N pool in the soil
resonance time of 1000 years
Lightning nitrogen fixation
3 x 10^12 g/yr
Turns SON into NH4+
Converts NH4+ to NO3
Converts NO3 to NO2, NO, or NO2
How great is the human impact on annual nitrogen fixation?
We have doubled it.
Increase in farm size from 1700 to 1980
Overuse of nitrogen causes:
1. smog
2. forest die-back
3. acidification of water
4. Ozone hole
5. Global warming
6. Eutrophication
an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia and severe reductions in water quality, fish, and other animal populations may occur.

Think about example with algae

Details and effects of NOx
-either NO or NO2
-created by denrification of nitrate (NO3-)
-produced by combustion (20Tg/yr)
-forms photochemical smog
-creates ground level ozone
-component of acid rain
-lives for 100 yrs in atmosphere
-destroys stratospheric ozone
-most destructive force on ozone right now because it is the only unregulated force
-radiative forcing contributes to global warming
-Causes slightly acidic rain
-mostly pollutes ocean shelf and estruaries
-About 40% caused by humans
Tropospheric Ozone
-Troposphere contains 10% of all ozone
-Toxic to plants and animals, but is usually diluted enough to not matter
-It’s fluxuations impact how crops and photosynthesis occurs
Stratospheric ozone
-UV shield
-Long term declien, particualry in antarctica
-N20 eats away at it
Montreal Protocol
-One of the first emission regulation cases.
-dealt with stratospheric ozone destruction in antarctica
-biggest flaw was that it didn’t regulate N20
-Hole is causing increased UV rays on surrounding ecosystems that affect all of the southern hemisphere
Effects of ozone destruction
2% increase in UVB for every 1% decrease in ozone. 2% increase in non-melanoma skin cancer for every 1% increase in UVB
-accounted for mostly by combustion (20Tg/yr)
-forms photochemical smog everywhere, even in Montreal
-creates ground level ozone
-component of acid rain
-comes mostly from fossil fuel use
-About 70% is emitted by humans
-animal waste accounts for 32 Tg
-Volitalization from soil accounts for 10Tg
-Forest burning releases 5Tg
-Raises the pH of rainwater
negative effects of increased nitrification in farms
-Nitrogen stays in system for a really long time
-can be leeched, released back to atmosphere, come down in acid rain, etc.
-effects are spread out and long-lasting
-N leaching leads to acidification +Al mobility
Ca depletion
acidification may explain red spruce decline (due to decreased cold tolerance) and sugar maple dieback on cation-poor soils
Positive ion
Hubbard Brook River Experiment
How N deposition affects diversity
Nitrogen addition leads to nitrate leaching into groundwater. Effects?
-denitrication takes nitrogen out of system
-leaching makes water undrinkable
-10ppm is unhealthy to drink (EPA standard)
-farmlands are at the highest risk of this leaching
Once N gets into water, where does it go?
30-70% of N entering rivers is denitrified
10-80% entering estuaries is denitrified
>80% entering shelves is denitrified
Hypoxia in coastal waters
-algal blooms caused by increased nitrogen due to increased photosynthesis
-when algae die, they sink to bottom. Their decomposition takes more oxygen out of the system
-*nitrogen doesn’t kill anything! They create things like algal blooms. oxygen produced by algal blooms diffuses oxygen out into the atmosphere. Their decomposition removes most or all oxygen from system, causing fish kills and the like
Light + CH20 + O2 => CO2 + H20

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Decomposition of biomass is opposite (minus the light)

What could we about emissions?
-Could cut down on fossil fuels and biofuels
-We could cut down on farm nitrogen runoff
-we don’t have the technology to regulate 75% of nitrogen
Nitrogen facts:
-only <1000 species can fix nitrogen (N2 => NH3)
-Key limitation to growth in many systems
-N2 is 78% of the atmosphere but is useless biologically
-chlorophyll A and B contain Nitrogen at their center
-critical in photosynthesis
Green revolution
-use of fertilizers (including nitrogen), pesticides, and irrigation
-tripled the green production around the world
Haber Bosch Process
Synthesis of ammonia to create nitrogen fertilizer. MOST IMPORTANT INVENTION OF THIS CENTURY!
-the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron catalyst, to produce ammonia
-ammonia is oxidized to turn it into nitrates and nitrites for fertilizers
-has made population 2x that that it would have been
Stratospheric Destruction
Sinks 12.5?±2.5?Tg?N?yr?1
Father of Gren revolution
Norman Borlaug (responsible for high yield crops) did shuttle breeding to start the green revolution
How much of annual crop yield goes to animals?
Roughly 40%
1kg of beef
20 kg of feed, 5% yield
1 kg pork
7.3 kg of feed, 14% yield
1 egg
4.5 kg feed, 22% yield
1 kg chicken
2.8 kg feed, 40% yield
1 kg milk
1.1 kg of feed, 91% yield
Feeding pigs in China?
Almost all increased production of soybeans in Brazil are going to feed pigs in CHina
How much do we need to increase food production? How?
We need a 50% increase in food production. We need 50% more land, 50% higher yields (through genetically modified organisms), change diet, have fewer people, waste less food
Forest distribution:
Regrowing in developed areas and disappearing in developing regions
How do we get more food?
More fertilizer won’t help in most (developed) places (soil is already saturated with it). Giving 1 bag of fertilizer to each farmer in Malawi increased yield though…
Percent of crops that are genetically modified in the US

70% of corn, nearly all of soybeans

Concerns with GMOs:
-GMO corns’ modified genes can jump to other native corn breeds (creating a homogenized version of corn)
0Weeds become adapted to our pesticides
Population curve
Logistical. Levels out at a particular carrying capacity
How do you find carrying capacity?
depends on water, energy, demographics, standard of living, etc.
Population Capacity
9.5 billion
IPAT equation
Impact = population x affluence x technology

affluence is consumption/capita
technology is impact per unit consumption

How do you find future populations?

P is base value, r is current growth rate, T is years into the future

Doubling time for anything exponential
70/(growth rate)
Growth rate trends
Low population: high br and high dr
As pop increases: lower dr and high birth rate
Large pop: low br and dr
Total fertility rate
much lower in developed world
-GDP/capita and total fertility rates have a correlation
-Education and TFR are correlated as well
Juxtaposition of Phosphorus
air to soil
Rock weathering
.3kgP/ha per year
-Phosphorus in soil.
-usually taken up by plants, excess bonds to clay and iron minerals
Phosphorus outputs
10 Ttg to start, weathering has doubled that (20Ttg), we started mining (18.5Ttg), so we in a sense quadrupled the amount of phosphorus inputs. ENDS UP WITH 15.5Ttg of P BEING ADDED TO FRESHWATER AND TERRESTRIAL ECOSYSTEMS
Time it takes for ‘lost’ phosphorus to cycle back
10^6-10^7 years
Natural rate of weathering:
total farmable land
1.5×10^9 ha
Natural output of Phosphorus vs human output of phosphorus
.45 x 10^9 kg/yr naturally
we put out 1.9×10^9 kg/yr