Ecological Perspectives on Critical Loads - Linkages between Emissions, Deposition and Biogeochemical Cycles

J. N. Galloway

Multi-Agency Critical Loads WorkshopUniversity of Virginia, May 2006

• The sulfur story– Biogeochemical cycle– Emissions and deposition– Sulfur cascade

• The nitrogen story– Biogeochemical cycle– Emissions and deposition– Nitrogen cascade

• Future considerations• Concluding thoughts

Topics

Global Atmospheric S Budget, Tg S yr-1

5

Dep

osit

ion

Dep

osit

ion

185

Fos

sil f

uel

smel

ters

7595

Land Coast Ocean

Nat

ura

l G

ases

10

Nat

ura

l P

arti

cula

te

20

Nat

ura

l G

ases

145

Nat

ura

l G

ases

25

Nat

ura

l P

arti

cula

te

•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.

Mackenzie, 2003

USA SO2 Emissions1860 - 2002

(million short tons/year)

05

10152025

3035

1850 1875 1900 1925 1950 1975 2000

Natural emissions

• 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.

EPA, various sources

Wet Deposition: SO4=

1994 2004

• Decreases in SO2 emissions have resulted in decreases in S deposition.• Again, current deposition is substantially greater than the natural rate.

NADP, 2006

Total S Deposition, 2002-2004 (kg S ha-1 yr-1)

•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

EPA, NADP, CASTNeT

Atmosphere

Terrestrial Ecosystems

Aquatic Ecosystems

Human Activities

- increases acidity of surface waters- causes loss of alkalinity and biodiversity

EnergyProduction

- increases regional haze, changes radiation balance- increases atmospheric removal rates of numerous species

SOx

People, Industry

The Sulfur Cascade

- stores sulfate; delays surface water acidification - H+ & Aln + acidify soil and decrease forest

productivity- Ca+ +, Mg+ +, K+ losses decrease forest

productivity

• The sulfur story– Biogeochemical cycle– Emissions and deposition– Sulfur cascade

• The nitrogen story– Biogeochemical cycle– Emissions and deposition– Nitrogen cascade

• Future considerations• Concluding thoughts

Topics

Grain Production

Meat Production

EnergyProduction

Nitrogen Drivers in 1860 & 1995

Nitrogen DepositionPast and Present

mg N/m2/yr

1860 1993

500020001000 750 500 250 100 50 25 5

Galloway and Cowling, 2002; Galloway et al., 2002b

Next, the North American Nitrogen Budget

North American N Budget, mid 1990s (Tg N yr-1)

N2

c-BNF, 6

fert.prod., 18North America

import, 5

fossil fuel, 7

BNF, 12

• 48 Tg N was introduced into North America, mostly as new Nr

Total Input ~48 Tg

NOy

North American N Budget, mid 1990s (Tg N yr-1)

N2

NOy NHx

c-BNF, 6

fert.prod., 18North America

4

35

2

import, 5

fossil fuel, 7

BNF, 12

• 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

Total Input ~48 Tg

North American N Budget, mid 1990s (Tg N yr-1)

N2

NOy NHx

c-BNF, 6

fert.prod., 18North America

4

35

2

import, 5export, 8

river, 7

atm. trans., 4

atm. trans., 1fossil fuel, 7

BNF, 12

• 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.

Total Input ~48 Tg Total Output ~20 Tg

USA NOx Emissions, 1860 - 2002 (million short tons/year)

0

5

10

15

20

25

30

1850 1875 1900 1925 1950 1975 2000

Natural emissions

• 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.

EPA, various sources

NADP, Wet Deposition: NO3-

1994 2004

What about that other N gas?

NADP, 2006

USA NH3 Emissions, 1994 - 2002(million short tons/year)

0

1

2

3

4

5

6

1850 1875 1900 1925 1950 1975 2000

• USA NH3 emissions are poorly known.• These data show a drop from 5 tons to 4 tons from 1994 to 2002.

EPA, various sources

NADP, Wet Deposition: NH4+

1994 2004

• Wet deposition data tell a different story.

• Let’s look at balance between wet and dry deposition for N species.

NADP, 2006

Total N Deposition, 2002-2004 (kg N ha-1 yr-1)

• 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

EPA, NADP, CASTNeT

There are significant effectsof 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.

Energy production

NOx

People(food; fiber)

Ozoneeffects

NHx

TerrestrialEcosystems

Norganic

Groundwatereffects

ParticulateMatter effects

Stratosphericeffects

N2OAtmosphere

Foodproduction

Surface watereffects

Oceaneffects

NH3

Aquatic Ecosystems

NO3

Soil

PlantAgroecosystemeffects

Soil

Crop Animal

Forests &Grasslands

effects

Indicates denitrification potential

Coastaleffects

NHxNOyNOx

Greenhouseeffects

N2O

N2O(terrestrial)

NHx

NOy

N2O(aquatic)

But denitrification also produces N2O. Gal

low

ay e

t al.,

200

3

NHx

Atmosphere

Forests

Head waters

Coastal waters

Nr

Nr

Nr

Nitrogen Biogeochemical Interactions

Atmosphere to Forests to Headwaters to Rivers to Coastal Waters

NOy

- increases forest productivity; sequesters C in biomass- H+ & Aln + acidify soil and decrease forest productivity- increases tropospheric O3 & GWP; decreases in stratospheric O3

Rivers

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

- increase in acidity of surface waters; loss of alkalinity and biodiversity- increase in tropospheric O3 & GWP; decreases in stratospheric O3

- increases in tropospheric O3 & GWP; decreases in stratospheric O3

- increase in HAB, loss of biodiversity, etc- increase in tropospheric O3 & GWP; decreases in stratospheric O3

Transfers

Galloway et al., 2003

• The sulfur story– Biogeochemical cycle– Emissions and deposition– Sulfur cascade

• The nitrogen story– Biogeochemical cycle– Emissions and deposition– Nitrogen cascade

• Future considerations• Concluding thoughts

Topics

Nitrogen DepositionPresent and Future

mg N/m2/yr

1993 2050

500020001000 750 500 250 100 50 25 5

Galloway et al., 2004

USA Relevance: New sources to west and south!

Nitrogen DepositionPresent and Future

mg N/m2/yr

1993 2050

500020001000 750 500 250 100 50 25 5

Galloway et al., 2004

USA Relevance: New sources to west and south!

0

10

20

30

40

50

60

0 100 200 300 400 500

Total Nr Created Tg N/yr

Nr Emitted to Atmosphere, %

Nr Creation Relative to NOx+NH3 Atmospheric Emissions

1860

1995

2050

• 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

• 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

Concluding Thoughts