Transcript Document

Ecological Perspectives on Critical Loads - Linkages between
Emissions, Deposition and Biogeochemical Cycles
J. N. Galloway
Multi-Agency Critical Loads Workshop
University of Virginia, May 2006
Topics
• The sulfur story
– Biogeochemical cycle
– Emissions and deposition
– Sulfur cascade
• The nitrogen story
– Biogeochemical cycle
– Emissions and deposition
– Nitrogen cascade
• Future considerations
• Concluding thoughts
Coast
25 145
185
Deposition
Natural
Gases
Land
5
Natural
Particulate
10
Natural
Gases
20
Natural
Gases
75
Natural
Particulate
Deposition
95
Fossil fuel
smelters
Global Atmospheric S Budget, Tg S yr-1
Ocean
Mackenzie, 2003
•Globally and in the USA, most of gaseous sulfur emitted is anthropogenic
•Even with large scale reductions in SO2 emissions, deposition will still be elevated
over natural conditions--i.e., enhanced S deposition is here to stay.
USA SO2 Emissions
1860 - 2002
(million short tons/year)
35
30
25
20
15
10
5
0
1850
Natural emissions
1875
1900
1925
1950
1975
2000
EPA, various sources
• USA SO2 emissions have dropped from peak of 32 tons in 1973, to
15 tons in 2002. The same as in 1905.
• This value is still 10 times greater than the natural rate.
Wet Deposition: SO4=
1994
2004
NADP, 2006
• Decreases in SO2 emissions have resulted in decreases in S deposition.
• Again, current deposition is substantially greater than the natural rate.
Total S Deposition, 2002-2004 (kg S ha-1 yr-1)
EPA, NADP, CASTNeT
•Both wet and dry S deposition are important
•Large uncertainties in dry deposition.
•Natural background, 0.4 to 0.8 kg S ha-1 yr-1
Atmosphere
SOx
- increases regional haze, changes radiation balance
- increases atmospheric removal rates of numerous species
Energy
Production
Terrestrial
Ecosystems
People,
Industry
- stores sulfate; delays surface water acidification
- H+ & Aln + acidify soil and decrease forest
productivity
- Ca+ +, Mg+ +, K+ losses decrease forest
productivity
Human Activities
The Sulfur
Cascade
- increases acidity of surface waters
- causes loss of alkalinity and biodiversity
Aquatic Ecosystems
Topics
• The sulfur story
– Biogeochemical cycle
– Emissions and deposition
– Sulfur cascade
• The nitrogen story
– Biogeochemical cycle
– Emissions and deposition
– Nitrogen cascade
• Future considerations
• Concluding thoughts
Nitrogen Drivers in 1860 & 1995
Grain
Production
Meat
Production
Energy
Production
Nitrogen Deposition
Past and Present
mg N/m2/yr
5000
2000
1000
750
500
250
100
50
25
5
1860
1993
Next, the North American Nitrogen Budget
Galloway and Cowling, 2002; Galloway et al., 2002b
North American N Budget, mid 1990s
(Tg N yr-1)
N2
fossil fuel,
7
BNF,
12
c-BNF,
6
fert.prod., 18
import,
NOy
North America
5
Total Input ~48 Tg
• 48 Tg N was introduced into North America, mostly as new Nr
North American N Budget, mid 1990s
(Tg N yr-1)
N2
fossil fuel,
NOy
7
NHx
4
2
5
BNF,
12
c-BNF,
6
fert.prod., 18
import,
3
North America
5
Total Input ~48 Tg
• 48 Tg N was introduced into North America, mostly as new Nr
• 9 Tg N of NOx was emitted to atmosphere, 5 re-deposited to continent
• 4 Tg N of NH3 was emitted to atmosphere, 3 re-deposited to continent
North American N Budget, mid 1990s
(Tg N yr-1)
N2
atm. trans., 4
atm. trans., 1
fossil fuel,
NOy
7
NHx
4
2
5
BNF,
12
c-BNF,
6
fert.prod., 18
3
North America
river, 7
export, 8
import,
5
Total Input ~48 Tg
Total Output ~20 Tg
• 48 Tg N was introduced into North America, mostly as new Nr
• 9 Tg N of NOx was emitted to atmosphere, 4.7 redeposited to continent
• 4 Tg N of NH3 was emitted to atmosphere, 3.0 redeposited to continent
• 20 Tg N in measured output; balance is either stored or denitrified.
30
USA NOx Emissions, 1860 - 2002
(million short tons/year)
25
20
15
10
Natural emissions
5
0
1850
1875
1900
1925
1950
1975
2000
EPA, various sources
• USA NOx emissions have dropped from peak of 25 tons in
1993, to 21 tons in 2002. The same as in 1970.
• This value is still 10 times greater than the natural rate.
NADP, Wet Deposition: NO31994
2004
NADP, 2006
What about that other N gas?
6
USA NH3 Emissions, 1994 - 2002
(million short tons/year)
5
4
3
2
1
0
1850
1875
1900
1925
1950
1975
2000
EPA, various sources
• USA NH3 emissions are poorly known.
• These data show a drop from 5 tons to 4 tons from 1994 to 2002.
NADP, Wet Deposition: NH4+
1994
2004
NADP, 2006
• Wet deposition data tell a different story.
• Let’s look at balance between wet and dry deposition for N species.
Total N Deposition, 2002-2004 (kg N ha-1 yr-1)
EPA, NADP, CASTNeT
• Both wet and dry N deposition are important
• Large uncertainties in dry deposition.
•Cloud N, Organic N and NH3 are missing!
• Natural background, 0.8 to 1.6 kg N ha-1 yr-1
There are significant effects
of Nr accumulation within the atmosphere, geosphere
and biosphere
Increases in:
- tropospheric O3, N2O & PM2.5
- soil acidity and N concentrations
- coastal water N concentrations
Decreases in:
- stratospheric O3
Lead to:
- loss of biodiversity in terrestrial and
aquatic ecosystems
- human health effects
- changes in earth’s radiation balance
These effects can be sequential, such that a
single atom of nitrogen could contribute to
them all, over time and space.
Str atospher ic
effects
Par ti cul ate
N 2O
Matter
effects
Greenhouse
effects
N2O
Atmosphere
Oz one
effects
NOx
Ener gy pr oducti on
Terrestrial
Ecosystems
Food
production
NH x
Forests &
Grasslands
effects
Agroecosystem
effects
Plant
NOy
N2O
(terrestrial)
Soil
Soil
NO3
People
(food; fi ber )
NHx
Animal
Crop
Norganic
NHx
NOy
NH3
Surface water
effects
Coastal
effects
N2O
(aquatic)
Aquatic Ecosystems
Ocean
effects
Groundwater
effects
Indicates denitrification potential
But denitrification also produces N2O.
Galloway et al., 2003
NOx
Nitrogen Biogeochemical Interactions
Atmosphere to Forests to Headwaters to Rivers to Coastal Waters
Transfers
Atmosphere
NHx
NOy
Forests
Nr
Consequences
- increases regional haze, changes radiation balance and impacts human health
- increases in tropospheric O3 & GWP; decreases in stratospheric O3
- increases/decreases GWP and decreases forest productivity
- increases forest productivity; sequesters C in biomass
- H+ & Aln + acidify soil and decrease forest productivity
- increases tropospheric O3 & GWP; decreases in stratospheric O3
Head waters
Nr
- increase in acidity of surface waters; loss of alkalinity and biodiversity
- increase in tropospheric O3 & GWP; decreases in stratospheric O3
Nr
- increases in tropospheric O3 & GWP; decreases in stratospheric O3
Rivers
Coastal waters
Nr
- increase in HAB, loss of biodiversity, etc
- increase in tropospheric O3 & GWP; decreases in stratospheric O3
Galloway et al., 2003
Topics
• The sulfur story
– Biogeochemical cycle
– Emissions and deposition
– Sulfur cascade
• The nitrogen story
– Biogeochemical cycle
– Emissions and deposition
– Nitrogen cascade
• Future considerations
• Concluding thoughts
Nitrogen Deposition
Present and Future
mg N/m2/yr
5000
2000
1000
750
500
250
100
50
25
5
1993
2050
USA Relevance: New sources to west and south!
Galloway et al., 2004
Nitrogen Deposition
Present and Future
mg N/m2/yr
5000
2000
1000
750
500
250
100
50
25
5
1993
2050
USA Relevance: New sources to west and south!
Galloway et al., 2004
Nr Emitted to Atmosphere, %
Nr Creation Relative to NOx+NH3 Atmospheric Emissions
60
50
2050
40
1995
30
20
1860
10
0
0
100
200
300
400
500
Total Nr Created Tg N/yr
• In 1860, 140 Tg N entered global terrestrial ecosystems; 20% was emitted to atmosphere.
• By 2050, almost 3 times as much N will be introduced, 50% of which will be emitted.
• The atmosphere is a growing transport medium for reactive nitrogen.
• In USA, changes in agricultural mix might increase NH3 emissions.
Galloway et al., 2004
Concluding Thoughts
• SO2 and NOx emissions have decreased
– The former is at the 1905 level.
– Both are still 10-fold greater than natural rates.
– Bottom line--S and N deposition are still an issue
in some regions of USA.
• S and N deposition is projected to increase over
the next few decades
– trans-boundary transport, SW and W
• Limits to knowledge
–
–
–
–
NH3 emissions
Dry deposition rates
Fate of deposited N (stored or denitrified?)
Sequential impacts of N