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Future riverine nitrogen export to US coastal areas: Prospects for improving
water quality amid population growth
Michelle McCrackin1,2, John Harrison2, Jana Compton3
National Research Council1, Washington State University2, USEPA3
December 12, 2012
NASA Earth Observatory
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Coastal ecosystem services
Millennium Ecosystem Assessment 2005
• Protection from flooding and storm events
• Maintenance of fisheries
• Nutrient cycling
• Water purification
• Recreation
NOAA
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Excess N in coastal ecosystems
• Reduced biodiversity
• Degraded water quality
• Harmful algal blooms
• Hypoxia
Hypoxic site Diaz 2011
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Question
How will population growth affect future N loads to US coastal areas?
NASA Earth Observatory
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• Nutrient Export from WaterSheds (NEWS) model
• 2030 scenarios
– Millennium Ecosystem Assessment
– Two additional scenarios
• “Business as usual”
• “Ambitious”
Seitzinger 2010
Future coastal TN loads
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T. Saxby, IAN Image Library
(ian.umces.edu/imagelibrary/)
Agricultural sources
Atmospheric deposition
Background N-fixation
In-stream
retention
N delivered to
basin mouth
Sewage
NEWS model: N transport
by rivers
Land-to-water
delivery
Storage/removal
on land
Mayorga 2010
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MEA scenario storylines
Globalization
Reacti
ve e
nvir
onm
enta
l m
anagem
ent
Global Orchestration
Technogarden
Pro
activ
e
enviro
nm
enta
l m
anagem
ent
Order from Strength
Adapting Mosaic
Regionalization
Millennium Ecosystem Assessment 2005; Seitzinger 2010
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Key scenario drivers
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
Population (million people)
297 370 375 375 375
Fertilizer recovery efficiency (%)
48 63 57 48 70
N in human excretion (kg N/person)
6.4 7.3 8.0 8.0 6.4
N removed by WWTP (%)
61 66 70 61 80
2000, AM, GO: Seitzinger 2010
BAU, AMB: Agriculture: Smil 1999; Sewage: Van Drecht 2009
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Scenario outcomes
2.7 2.6 2.8 3.2 2.2
Particulate
Natural
Sewage
Atmospheric
deposition
Agriculture
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Scenario assumptions in context
• Scenarios reflect interaction of
–Socio-economic factors
–Nutrient management practices
• Compared assumptions to
–US agency publications
–Scientific literature
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Population growth
• Population growth drives increases in
– Crop production
– Fossil fuel combustion
– Sewage
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
Population (million people)
297 370 375 375 375
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Population growth
• Population growth drives increases in
– Crop production
– Fossil fuel combustion
– Sewage
• US Census Bureau
– 2012: 312 million
– 2030 projection: 373 million people
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
Population (million people)
297 370 375 375 375
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Fertilizer recovery efficiency
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
Fertilizer recovery efficiency (%)
48 63 57 48 70
MARB Hypoxia Task Force 2011
Since 2000, additional 28 m acres under some form of nutrient management
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Fertilizer recovery efficiency
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
Fertilizer recovery efficiency (%)
48 63 57 48 70
• ~35% of US cropland meet BMPs for rate, timing, and method of fertilizer application
• Typical fertilizer recovery efficiencies ~50%
• Future improvements appear optimistic
Cassman and Doberman 2002; Ribaudo et al. 2011
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Dietary preferences
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
N in human excretion (kg N/person)
6.4 7.3 8.0 8.0 6.4
• Strong, positive relationship between wealth and food consumption
Van Drecht 2009; Kearney 2010
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Dietary preferences
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
N in human excretion (kg N/person)
6.4 7.3 8.0 8.0 6.4
• 2000-2010 trends
–Meat consumption down 5%
–Total food consumption flat
• Effects of economic conditions or changes in dietary preferences?
2012 US Statistical Abstract
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Sewage treatment effectiveness
2000 2030 AM
2030 GO
2030 BAU
2030 AMB
N removed by WWTP (%)
61 66 70 61 80
EPA Clean Watersheds Needs Survey, 2008
• States planning for 66% N-removal efficiency
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Time lags
• NEWS model structure assumes N is in steady-state
• Evidence of N accumulation in managed landscapes
– 30 y time lag between N input and export for River Thames
– >20 y of N management in Europe, but no consistent reductions in coastal export
Howden 2011; Grizzetti 2012
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Conclusions
• Substantial changes in nutrient
management needed
- Technologies and BPM’s exist today
to reduce coastal N loads
- Reducing agricultural N will have the
greatest coastal benefit
• Policies must take decadal perspectives
• Degradation of coastal ecosystems and services likely to continue
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NASA Earth Observatory
Questions
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NOx emissions have declined
USEPA Acid Rain Program 2010