nutrient pollution. eutrophication from the greek: “eutrophos,” meaning “well-nourished”...
TRANSCRIPT
Nutrient Pollution
Eutrophication
• From the Greek: “eutrophos,” meaning “well-nourished”
• “Cultural eutrophication” means that we caused it
The Nitrogen
Cycle
All life requires nitrogen compounds – e.g. to make amino acids, which build proteins.
Nitrogen gas, N2, makes up 79% of the atmosphere, but is it inert.
Nitrate and ammonia can be used by plants, but it requires a great deal of energy to break apart N2 molecules.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NitrogenCycle.html
The Nitrogen
Cycle
“Nitrogen Fixation”
We can make ammonia in factories, using atmospheric nitrogen and hydrogen (usually from natural gas or petroleum).
Requires great pressure, and temperatures of 600 degrees C!
Lightening can do the same thing (makes about 5-8% of the total nitrogen fixed.
Ammonia factory• “National Public
Radio reports that low cost Anhydrous Ammonia is the single greatest technical development of the last 200 years. At least 2 times more land in the US would need to be in production to feed only our citizens if low cost Anhydrous Ammonia was not available.”
Source: http://www.exactrix.com/dewi.htm
We have become the dominant source of nitrogen fixation on the Earth – partly by making
fertilizer
The Nitrogen
Cycle
Certain bacteria have also figured out how to fix nitrogen.
Requires a huge expenditure of ATP.
Nitrogen-fixing bacteria usually live in a symbiotic relationship with legumes.
Cyanobacteria can also do this in aquatic systems.
We have become the dominant source of nitrogen fixation on the Earth – partly by growing
legumes
The Nitrogen
Cycle
Other bacteria, particularly ones living in anaerobic conditions, use nitrate as a substitute for oxygen in their metabolism.
They produce N2 gas as a by-product.
Human Population• Causes of lower
rates:• Economic
stringencies • Availability of birth
control• Emergence of
women’s rights• Delayed first
reproduction• Demand for more
education• Lower infant
mortality• Social security
Source: Valiela, Data from Pop. Ref. Bureau and UN
Note that the rate of population growth did NOT decrease because
of pollution.
0
2
4
6
8
10
1950 1970 1990 2010 2030 2050
Worl
d p
op
ula
tion e
stim
ate
and
pro
jection
(x 1
09 )
Rural
Urban
Data from Pop. Ref. Bureau and UN
• By 2050, ~30% more people
• By 2030, ~60% of world population will be living in urban areas
From Valiela (2005). Global Coastal Change,Blackwell Science Publ. Data from Van Breemen et al. (2002), and Dow and Dewalle (2000).
• Land use on watersheds ischanging fast
• Tendency for urbanization to increase
From Nicholls and Small (2002), and Valiela et al. (1992)
Population is Coastal
European watersheds
Waquoit Bay watersheds
Data of Garnier et al. (2002).From Valiela et al. (2000).
0
600
1200
1800
2400
3000
0 100 200 300 400 500
People per km2
Kg
N o
r P
pe
r km
2 y-1
Nut
rient
exp
ort (
kg k
m-2y-1
)
Land
use
(ha
)
600
900
1200
1500
Human uses
0
200
400
600
800
1920 1940 1960 1980 2000
Turf
Imperv.Surf.
Agriculture
3300
3600
3900
4200
Natural veg.
Changes in land use on the watershed of Waquoit Bay on Cape Cod Massachusetts, 1938-1992.
From Valiela and Bowen (2002)
Nitr
ogen
inpu
ts (
10 3
kg N
y-1
)
1940 1950 1960 1970 1980 1990
40
80
120
160
200
4
8
12
16
20
24
Year
To the watershed
To the estuary
Total
Atmospheric
Wastewater
Fertilizer
Total
Atmospheric
Wastewater
Fertilizer
N in
puts
(10
3 k
g N
yr-1
)
From Bowen and Valiela (2001)
N and P enrichment experiments.N and P enrichment experiments. Example results from a trial in Jobos
Bay, PR, Teichberg et al.
% growth (mean ± s.e.)Treatment Ulva Gracilaria
C 128 ± 21 12 ± 10
P 111 ± 16 11 ± 3
N 305 ± 57 42 ± 8
ControlNitrate
Phosphate Control
Venice, Italy
Photo by M. Teichberg
Increases in primary production —owing to increased nitrogen supply—are associated with increases in secondary production (fish, in this case).
From Nixon and Buckley (2002)
Final thoughts…
• Nitrogen, once added to a marine ecosystem, can be cycled through many times, potentially contributing to hypoxia each time (see next week’s lecture).